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8 The Psychological Effects of Breastfeeding

Published onJul 01, 2018
8 The Psychological Effects of Breastfeeding
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8 The Psychological Effects of Breastfeeding


Jennifer Hahn-Holbrook, PhD

Expected Key Learning Outcomes

  • The importance of breastfeeding for mother and infant well-being

  • The psychological impact of breastfeeding on the mother and her infant

  • The influences on a mother’s decision to breastfeed

8.1 Introduction

Breastfeeding confers a plethora of psychological benefits to both mothers and their infants. However, while breast milk is widely appreciated as the ideal nutritional source for developing infants, the psychological benefits of breastfeeding are often overlooked. Expectant mothers are besieged with opinions and facts related to the costs and benefits of breastfeeding. Most of this information pertains to infant health, leaving mothers unaware of the potential psychological benefits of breastfeeding. Studies show that women are generally aware that breastfeeding carries potential advantages for their infant’s intelligence and immune functioning, but unaware that it dampens the maternal stress response and doubles the amount of slow wave sleep that mothers enjoy [1], [2]. Ironically, breastfeeding is also perceived as an onerous sacrifice undertaken by mothers to nurture their children, whereas the emerging science highlights ways in which breastfeeding aids new mothers in meeting parenting challenges.

Herein, emerging insights from experimental, epidemiological, and comparative research are highlighted to provide an evidence-based overview of the effects of breastfeeding on mothers. Additionally, some of the psychological impacts of breastfeeding for infants and mother-infant dyads, and the significant cultural and psychological impediments to breastfeeding are addressed and proposals made to surmount these obstacles.

The chapter starts with a brief overview of how hormones broadly shape maternal psychology during breastfeeding. The next sections focus on the mother, reviewing what is known about how breastfeeding impacts maternal stress regulation, postpartum depression risk, bonding, sensitivity to infant cues, sleep disturbances, and defence of the infant. This is followed by a review of the effects of breastfeeding on infant psychology, covering topics ranging from infant attachment to maternal programming of infant temperament through bioactive hormones in mothers’ milk. Moving the focus back to the mother, some of the psychological barriers to breastfeeding, such as cultural taboos about public lactation, partner opposition to breastfeeding, postpartum depression, and maternal guilt at breastfeeding “failures”, are discussed. We conclude with a summary of the psychological benefits that breastfeeding can and cannot offer mothers and their babies.

8.2 Psychological Implications for Mothers

8.2.1 Oxytocin and Prolactin

The hormonal and biological changes during lactation mediate many of the benefits of breastfeeding for mothers. Lactation is a biologically unique period in the female lifespan, characterised by hormonal shifts, suppression of reproductive function, and changes in metabolic processes. The two most important hormones associated with lactation are oxytocin and prolactin. Oxytocin facilitates smooth muscle contractions during labour and enables the release of milk during lactation. Prolactin is primarily responsible for the production of breast milk. Prolactin levels gradually rise over the course of pregnancy, eliciting changes in breast tissue that stimulate milk production. Oxytocin levels also rise, eventually quadrupling to stimulate labour [3]. After birth, prior to breastfeeding, oxytocin aids milk ejection [4].

A mother’s body appears evolved to take infant stimuli as cues to release oxytocin in anticipation of feeding, as mothers who have been separated from their infants prior to feeding do not display this anticipatory oxytocin release [5]. As the nipple receives tactile stimulation during feeding, oxytocin and prolactin are released in pulses controlled by nerve fibres linked to the hypothalamus [6]. Relative to non-breastfeeding women, breastfeeders typically display higher prolactin levels, indicating that prolactin levels are modulated by breastfeeding frequency and infant demand for milk [7]. Oxytocin levels remain elevated for a short time after each breastfeeding session but return to baseline relatively quickly [6].

Although oxytocin and prolactin are widely appreciated as key biological mediators of birth and lactation, researchers are now beginning to understand the significance of these hormones for maternal psychology and behaviour. Oxytocin and prolactin circulate within the brain, activating specialised receptors across diverse brain regions, and hence should be expected to influence mental as well as physical outcomes [8], [6]. Indeed, comparative studies in nonhuman animals point to the contributions of oxytocin and prolactin in critical maternal behaviours such as grooming, defensive aggression, and sensitivity to infant cues [8], [6]. As such, there are strong grounds to expect them to also influence human maternal thoughts, feelings, and actions.

8.2.2 Maternal Bonding

Mother-infant bonding is one of the chief motives to breastfeed reported by women [9]. The same sentiment is often echoed within the scientific literature, where breastfeeding is frequently assumed to foster maternal bonding (e.g., [10]). Despite this, strikingly few studies have actually investigated this question. In this section, the modest literature on lactation and mother-infant bonding is discussed, with an emphasis on animal studies in light of the dearth of human studies. This section focuses on maternal bonding, while subsequent sections focus on the effects of breastfeeding on infant attachment to the mother.

Across mammalian species, lactation has been found to be critical for eliciting maternal behaviour because it triggers release of oxytocin and prolactin [11]. Upon injection of oxytocin [12] or prolactin [13] into the brain, female rats exhibit maternal behaviours. Conversely, maternal behaviours are significantly reduced if oxytocin or prolactin blocking agents are injected into the rat brain shortly after giving birth [14], [15]. However, lactation-induced hormonal shifts appear less crucial for instigating maternal behaviours in nonhuman primates, in whom early developmental and social experience make larger contributions [16]. Similarly, in Rhesus monkeys, oxytocin antagonists introduced into the brain impair certain maternal behaviours, yet leave others intact [17].

Many observations in non-human primates indicate that maternal behaviours can emerge without lactation, as in cases where females without offspring of their own carry and groom infants [18]. In humans, breastfeeding is unnecessary to establish maternal bonding, as attested by the exceptional caregiving shown by formula-feeding mothers, fathers, adoptive parents, and extended family. However, it may be hypothesised that lactation enhances certain caregiving behaviours, particularly in challenging circumstances.

Studies in humans demonstrate that oxytocin facilitates maternal bonding. Plasma oxytocin levels measured during both pregnancy and postpartum are predictive of behaviours related to maternal bonding, including maternal vocalisations, feelings of positive affect, eye gaze directed at infants, affectionate infant touching, and attachment-related ideation [19]. Furthermore, mothers who engage in more frequent (compared to less frequent) affectionate touching while playing with their children have elevated oxytocin levels [20]. These findings suggest that breastfeeding may intensify positive maternal behaviours to the extent that lactation stimulates bursts of oxytocin. Indeed, of five studies that test whether breastfeeding promotes maternal bonding, four have found some supportive evidence (see Martone & Nash 1988 for a null result [21]).

Else-Quest and colleagues observed mother-infant interactions at 4 and 12 months after giving birth, and found that breastfeeders showed more positive and rich mother-infant interactions at 12 months (but not at 4 months) than mothers who never initiated breastfeeding [22]. In another study, mothers who provided more than half of their infant’s nutrition via breast milk for the first 5 months after birth reported greater levels of emotional bonding with their babies in comparison to mothers who provided less than half of their infant’s nutritional needs via breastfeeding, or who did not breastfeed at all [23]. Additionally, mothers who were not breastfeeding at 3 months following birth reported less sensitivity to their babies’ needs than women who were breastfeeding up to that time [24]. Recently, Jonas and colleagues found that women who were breastfeeding at 3 months were rated by independent observers as more sensitive to their infant’s needs during a 30-minute infant interaction at 6 months than mothers who were not breastfeeding at 3 months [25]. Interestingly, the association between breastfeeding and heightened maternal sensitivity was only observed in mothers who reported a high level of psychological stress. Mothers who reported very little psychological stress exhibited a high level of maternal sensitivity regardless of their breastfeeding behaviours at 3 months. These results raise the intriguing possibility that breastfeeding may be especially important in facilitating maternal sensitivity when mothers are facing stressors, which can undermine parenting behaviours.

While consistent with the hypothesis that breastfeeding facilitates maternal bonding and caregiving, the above findings warrant caution as few studies corroborate maternal behaviour with objective observations. In addition, it may be the case that mothers who elect to breastfeed are dispositionally more attuned to their infants or are more prone to self-report greater sensitivity. Consistent with these alternative interpretations, studies have shown that mothers who expressed the intention to breastfeed during their pregnancies also reported greater maternal sensitivity at 3 months [26], and that willingness to breastfeed is correlated with the strength of the mother-infant bond. For example, the quality of mother-infant bonding behaviour observed 2 days after giving birth has been found to predict exclusive breastfeeding at 6 months after birth [27]. It is also important to consider that, although there may be benefits of breastfeeding for maternal sensitivity, mothers who had never breastfed in the above studies exhibited levels of maternal sensitivity that were well within the normal clinical range [22]. Thus, the question is not whether breastfeeding is necessary, but whether it is helpful, especially under conditions of maternal stress.

To summarise, existing evidence provides limited support for the hypothesis that breastfeeding promotes maternal bonding. Prospective or experimental studies, as well as objective measures of maternal bonding, should be employed to resolve this important question.

8.2.3 Maternal Stress Regulation

Caring for an infant can be intensely stressful, with maternal stressors ranging from psychosocial preoccupations with being a “good” mother [28] to physical challenges such as sexual dysfunction and sleep deprivation [29]. New mothers find themselves responsible not only for their baby’s welfare, but also for the simultaneous demands of partners, other children, themselves, and career needs [30]. Although often offset by the intrinsic rewards of parenting, mothers also appear to experience sustained, heightened vigilance toward potential hazards to their children, which is related to activation of neurobiological stress systems [31]. In light of the demands of parenting, it is of little surprise that about 20% of new mothers report depressive symptoms within the first year after giving birth [32]. Fortunately, nature may have crafted breastfeeding to help manage this stressful period [33], [34].

Converging lines of evidence indicate that breastfeeding modulates maternal stress responses [34], [35], [36]. Initial evidence derived from rodent studies showed that lactating rats were remarkably resistant to stress relative to non-lactating rats, as measured by reduced hormonal and cardiovascular signs of anxiety in response to electric shocks, frightening predators, or complex mazes [37].

Human studies have found comparable negative associations between breastfeeding and stress. Breastfeeding human mothers exhibit significantly diminished hormonal stress responses (i.e., lower cortisol and adrenocorticotrophic hormone levels) during stressful physical exertion compared with non-breastfeeding mothers or women who have never given birth [38].

Subsequent studies have examined cardiovascular and hormonal stress responses to the Trier Social Stress Task, in which the participant delivers a public speech and performs mental arithmetic in front of a critical audience. These investigations often fail to report lower stress reactivity using hormonal markers but repeatedly show lower cardiovascular stress reactions in breastfeeding mothers relative to formula-feeding mothers. Altemus and colleagues found that breastfeeders exhibited reduced markers of cardiovascular stress (e.g., higher cardiac parasympathetic control, lower basal systolic blood pressure [SBP]) during the Trier task when compared with formula-feeding mothers or women without children [39], and a complementary study reported similar cardiovascular benefits for breastfeeding mothers during the period of anxious anticipation prior to the social stress task [40]. Stress-attenuation related to breastfeeding may be particularly evident in the period immediately following a breastfeeding session, caused by the breastfeeding act rather than by simply holding one’s infant. Indeed, mothers who breastfed before the Trier task were found to produce blunted hormonal cortisol responses relative to breastfeeding women who were instructed to hold their babies [41].

Beyond the social domain, the stress-attenuating benefits of lactation appear to generalise to other sorts of challenges. In a seminal study, cardiovascular reactions to hand immersion into painfully cold ice water were compared in exclusively breastfeeding women, exclusive formula-feeding women, women who used both breast milk and formula, and women who had never given birth [42]. Mothers who breastfed more frequently each day had reduced sympathetic reactivity in response to the painful water immersion task when compared with mothers who breastfed less frequently, suggesting a dose-dependent relationship between breastfeeding and stress reduction. Interestingly, the stress-reduction benefits of lactation decreased with time: Breastfeeders with children older than 1 year appeared to derive less stress-attenuation when compared with breastfeeders of younger children. This suggests that the beneficial effects of breastfeeding for mothers track the period of greatest child vulnerability and dependency, potentially reflecting evolutionary design to help new mothers cope.

Additional research supports the theoretical benefits of breastfeeding with regard to everyday stress. Formula-feeding mothers report experiencing less positive mood states, less emotional equanimity, and greater anxiety than breastfeeders [43], [33], [44], [45], [41]. These differences withstand after statistically accounting for likely confounding factors such as maternal age, income, health behaviours, and employment status [46], [47], [48].

The reductions in stress associated with breastfeeding are theoretically driven by oxytocin and prolactin. However, although rodent studies provide robust experimental evidence that lactation related stress-reduction is mediated by oxytocin [49], [50] and prolactin [51], [8], findings in humans are supportive but correlational. For example, higher plasma oxytocin and prolactin measured during the early postpartum period are predictive of reduced self-reported anxiety [52], [53], and breastfeeders who release higher levels of oxytocin in response to suckling have reduced cortisol levels [54]. Furthermore, breastfeeders with higher levels of oxytocin exhibit markedly reduced indications of stress when anticipating the Trier social stress task when compared with breastfeeders with lower levels of oxytocin [40].

In summary, both studies in humans and comparative studies of non-human animals indicate that physiological stress responses are buffered by lactation. These effects appear to be related to increases in the hormones oxytocin and prolactin, although direct evidence that these hormones mediate stress reduction in humans is sparse. In human mothers, the stress-attenuating benefits of lactation also seem to be most pronounced in the early postpartum period or immediately following individual feeding sessions. Cardiovascular assessments of sympathetic and parasympathetic nervous system activity reveal more consistent differences in stress reactivity between lactating women and control women than do assessments of hormones related to the hypothalamic-pituitary adrenal axis (e.g., cortisol).

Arguably, the most straightforward measure of the effects of breastfeeding on stress, mood, and emotion derives from self-reports. Consistent with the biological data, breastfeeding mothers report experiencing less stress and negative affect in their daily lives when compared with formula feeding mothers.

8.2.4 Maternal Coping Strategies

The postpartum period is characterised by severe sleep disturbance, constant efforts to understand infant’s needs, and frequent concerns about the baby’s safety and wellbeing. These challenges have been faced by lactating mammals for millions of years, and research suggests that, over generations, adaptations may have emerged to help breastfeeding mothers get better sleep, decipher infant cues, and defend their infants [55].

Breastfeeding mothers get twice the amount of slow wave sleep (“deep sleep”) at night compared to formula-feeding mothers or women without children. In a study by Blyton, et al., the sleep patterns of 12 exclusively breastfeeding mothers were compared to 12 women without children and seven mothers who were bottle-feeding their infants [56]. Although the total amount of sleep time and time spent in rapid eye movement sleep were similar in all groups, breastfeeding mothers had an average of 182 minutes of slow wave sleep, more than twice that found in the control (86 minutes) and bottle-feeding mothers (63 minutes). There was a compensatory reduction in light non-rapid eye movement sleep in the breastfeeding group. The high circulating levels of prolactin in breastfeeding mothers was most likely responsible for their altered sleep pattern. The fact that breastfeeding promotes longer time in deep, slow wave sleep may be an adaptation to allows new mothers to cope with the frequent night waking caused by young infants.

Other studies suggest that, even though breastfeeding babies wake more frequently to feed because breast milk is digested more rapidly than formula, breastfeeding mothers get slightly more sleep on average than formula-feeding mothers, presumably because breastfed infants settle more quickly than formula fed infants [57].

Breastfeeding is also associated with increased sensitivity to infant cues. It is not known whether this heighted maternal sensitivity is mediated directly through breastfeeding hormones or because breastfeeding facilitates more frequent close contact between mothers and babies. Using functional MRI, the brains of 17 exclusively breastfeeding and exclusively formula-feeding mothers were monitored during exposure to cries from their own and unfamiliar infants [58]. In the first postpartum month, breastfeeding mothers showed greater activation in response to their own infants cry in brain regions implicated in maternal-infant bonding and empathy compared to formula-feeding mothers. Additionally, in a large, longitudinal study of 675 mother-infant pairs [59], mothers who breastfed for longer periods were more sensitive to infant cues of distress at 14 months than mothers who breastfed for shorter durations [59]. Enhanced sensitivity to infant cues by breastfeeding mothers in the early postpartum period could help them (especially new mothers) cope with understanding the needs of their infant. Additional research is needed to clarify the specific role that lactation plays in attuning the maternal brain to her child.

Evidence also suggests that lactation helps mothers defend their infants under attack. Many people are familiar with the adage ‘don’t come between a mamma bear and her cubs’, although the saying ’don’t come between a lactating mamma bear and her cubs’ would be more accurate. Sometimes referred to as maternal defence, maternal aggression or lactation aggression, this period of heightened defensive aggression in mothers after birth is directed toward rival members of the same species (conspecifics) and predators, and typically follows the course of lactation [60]. Maternal defence has been documented in rats and mice [60], prairie voles [61], hamsters [62], lions [63], domestic cats [64], rabbits [65], squirrels [66], and domestic sheep [67]. Among primates, lactating Japanese and Rhesus Macaques display more aggression than females at any other reproductive stage [68], [69], [70].

To test whether lactating human mothers display heightened levels of aggression, women’s willingness to deliver aversive sound bursts to a hostile female confederate was compared between breastfeeding, formula-feeding, and nulliparous women [71]. The comparison was made using a competitive game, where aggression was assessed by the combined volume and duration of sound bursts participants inflicted on the confederate who had previously delivered many loud sound blasts to all participants [72]. As predicted, breastfeeders inflicted significantly more aggressive retaliatory sound bursts than formula-feeding or nulliparous women.

In rats, lactation disinhibits aggressive behaviours toward potentially threatening conspecifics by triggering the release of stress-attenuating hormones (oxytocin and prolactin), which has been suggested to reduce mothers’ fear during attack [73], [74]. Convergently, mothers with lower SBP (a proxy of less physiological stress) during an aggressive encounter tended to be more aggressive [71]. Breastfeeding mothers also had lower SBP during the encounter than the bottle-feeding or nulliparous groups, and less SBP reactivity to the encounter compared to baseline. Finally, the stress reducing properties of lactation were found to account for much of the heightened aggression observed in breastfeeding mothers, compared to the bottle-feeding or nulliparous women.

In sum, breastfeeding appears to increase mothers’ willingness to react aggressively when they or their offspring are under threat. However, lactating mothers do not go looking for fights; lactation aggression likely operates only to promote defensive forms of aggression for protection.

8.2.5 Postpartum Depression

Postpartum depression afflicts approximately 13% of western mothers within the first 3 months after giving birth [75]; the global prevalence rate is unknown but appears to vary considerably across cultures [76]. Postpartum depression should not be confused with either the relatively short-lived postpartum mood disorders such as the ‘postpartum blues’, which affect between 50% and 80% of western mothers [77], [78], or the serious but rare disorder of postpartum psychosis [79]. Postpartum depression is characterised by feelings of hopelessness, despair, detachment, anxiety, and guilt. Postpartum depression can lead to long term negative child outcomes with regard to cognitive, emotional, and behavioural development [80], as a result of disrupted parenting behaviours during the critical period of early development [81]. Given the beneficial effects of breastfeeding on stress regulation and maternal sensitivity, links between lactation and postpartum depression have been investigated.

Systematic reviews of the literature have identified numerous studies reporting higher rates of postpartum depression in formula-feeding mothers in comparison with breastfeeding mothers [82], [83]. Although these data support the premise that breastfeeding buffers against postpartum depression, further studies are needed to address causality – does weaning increase mothers’ risk for depression or does depression cause mothers to wean? Breastfeeding mothers may be protected against postpartum depression but mothers with depression in pregnancy or early postpartum may be less likely to breastfeed. The former is discussed here, the latter under psychological barriers to breastfeeding.

There are sound reasons to expect breastfeeding to protect against postpartum depression. Breastfeeding triggers the release of oxytocin, and higher oxytocin levels have been found in mothers without depression than in those with depression [84]. Consistent with the notion that momentary increases in oxytocin triggered by breastfeeding might suppress negative affect, mothers who feed their infants both breast milk and formula self-report lower levels of negative mood immediately following breastfeeding than after formula feeding [48]. Regardless of whether these benefits are mediated by oxytocin, breastfeeding is robustly associated with reduced stress [36], which is one of the biggest risk factors for postpartum depression [85]. Also, infants with health concerns can constitute a significant source of stress, and formula-fed infants tend to have greater health problems over the long term [86]. Thus, the ill effects of formula feeding on infant health may indirectly increase maternal stress, and the related risk of postpartum depression.

Some of the strongest evidence suggesting that breastfeeding is protective against postpartum depression comes from a study of 205 mothers who were asked about depressive symptoms prenatally, and about their breastfeeding behaviours and depressive symptoms repeatedly up to 24 months after giving birth [87]. Mothers who breastfed more times per day at 3 months postpartum had greater reductions in depressive symptoms than women who breastfed fewer times per day at 3 months, even after prenatal depressive symptoms were taken into account. The study suggests that there is a dose-response relationship, whereby a larger degree of early breastfeeding provides a larger degree of protection against latter depressive symptoms. Other studies have found similar protective effects of breastfeeding against subsequent depressive symptoms [83]. Early weaning [23]
and never initiating breastfeeding [88], [89] have both been found to predict the onset of postpartum depression. However, duration of breastfeeding is likely important, one prospective study found no association between breastfeeding behaviour at 1 week and subsequent depressive symptoms at 4 and 8 weeks postpartum [90].

In summary, current research suggests that breastfeeding may be protective against postpartum depression but experimental studies are necessary to establish causality and investigate potential mediators of this association. However, as discussed later in this chapter, depression in pregnancy or in the early postpartum can be a barrier to breastfeeding. The relationship between breastfeeding and postpartum depression is therefore complex and bidirectional. Ironically, the women who would benefit most from the antidepressant actions of breastfeeding (i.e., those depressed during pregnancy) are less likely to both initiate and maintain breastfeeding.

8.3 Psychological Impacts of Breastfeeding on the Infant

8.3.1 Attachment

Breastfeeding provides much more than just good nutrition for the developing infant. It provides direct skin-to-skin contact between mother and child, encourages early maternal-child social exchanges, and triggers the infant’s natural sucking reflex, calming the infant. For all these reasons, scientists have posited that breastfeeding facilitates the child’s attachment to the mother. Surprisingly few studies have investigated the impact of breastfeeding on infant attachment, and those that have tend to find no long-term effect of breastfeeding [10]. In a study of 152 mother-infant pairs examining the association between breastfeeding initiation/duration and the quality of 12- month-old infants’ attachment to their mother, breastfed infants were no more likely to be securely attached to their mothers than formula-fed infants [24]. This is perhaps not surprising, given that it is important for human infants to form attachments with many caregivers (fathers, grandparents, etc.) who do not provide breast milk. However, this is not to say that breastfeeding is unimportant to the mother-infant relationship; the study also showed that breastfeeding mothers were more sensitive to their infant’s cues than were formula-feeding mothers.

Research suggests that breastfeeding may accelerate development of the infant’s preference for and recognition of their mother. In a series of studies, 2-week-old breastfed babies were compared with bottle-fed babies in their preference for the smell of their own mother over that of unrelated breastfeeding women [91]. Babies were exposed simultaneously to two gaze pads placed on either side of their heads, one of which had been worn under the arm of their mother for 8 hours, while the other was worn by an unfamiliar breastfeeding female. Breastfed babies were more likely to orient their bodies towards the scent of their own mother, whereas formula-fed babies showed no preference, suggesting earlier recognition of their mother’s scent by breastfed babies. The authors hypothesised that breastfeeding facilitates more maternal-infant skin-to-skin contact than bottle-feeding, which may give breastfed babies increased exposure to their mother’s unique olfactory cues and speed their preference for their mothers over other caregivers.

8.3.2 Temperament

The relationship between breastfeeding and infant temperament is complex, and the evidence is contradictory. A cross-sectional study of 655 infants aged 6–24 months found higher levels of socioemotional development (a composite of measures related to self-regulation, ability to communicate needs, and establishing social relationships) in exclusively breastfed compared to exclusively formula-fed infants, according to maternal reports [92]. Another study, however, found that breastfeeding mothers reported that their infants were more demanding, cried more often, and smiled less often than formula-feeding mothers [93]. Reports by breastfeeding mothers of their babies having more difficult temperaments may be because of the greater vigour and intensity of reactivity observed in breastfed infants [94], resulting from the superior nutritional content of breast milk and more rapid weight gain of breastfed compared to formula-fed infants. Alternatively, it may be because breast milk is digested more quickly than formula and milk volume is regulated by infant suckling [93], causing breastfed infants to exhibit more cues of hunger to initiate feeding than formula-fed infants. A large longitudinal study of 30,466 Norwegian mothers found negligible effects of breastfeeding on later temperament or difficult temperament on later breastfeeding [95].

Although the literature to date does not show any lasting association between breastfeeding and infant temperament, prospective evidence suggests that breastfeeding may offer children some long-term protection against mental health disorders. Oddy and colleagues followed 2,900 infants from birth to 14 years of age, noting obstetric risk factors for mental illness (preterm birth, advanced maternal age), exposure to early life stressors, mother’s mental health status postpartum, and changing family composition and income [96]. After accounting for these confounding variables, children that had been breastfed for more than 6 months were less likely to experience internalising mental health problems (e.g., being withdrawn, anxious/depressed, or having somatic complaints) and externalising mental health problems (delinquent or aggressive behaviour) at 14 years old, than children that had been breastfed for fewer than 6 months.

Additionally, emerging research suggests that exposures to bioactive hormones through breast milk may shape infant temperament. Breast milk contains a number of hormones that may program infant psychological development [97], [98]. As such, lactation may be regarded as a fourth trimester during which time breast milk provides a direct biological connection between the endocrine systems of the mother and infant.

Human infants exposed to higher levels of cortisol in their mother’s milk scored higher in negative affect than infant’s exposed to lower levels, although this correlation was stronger in girls than in boys [99]. Neither environmental factors (e.g., maternal education, age, and social economic status) nor negative maternal affect (e.g., depression and perceived stress) at 3 months postpartum accounted for this correlation. Similar results have been reported in rhesus macaques [100]. Specifically, higher levels of milk cortisol in macaques predicted more confident temperaments in both sons and daughters, independent of available milk energy. Another study in humans found that the circulating cortisol levels in mothers and infants were more closely correlated in breast-fed mother-infant pairs compared to formula-feeding mother-infant pairs [101].

Together, these findings suggest that exposure to elevated cortisol levels in breast milk may shape infant temperament in humans, and that mothers have the ability to tune their infant’s temperament through transmission of biologically active components in milk.

8.4 Psychological Barriers to Breastfeeding

A mother’s decision to breastfeed or not is a topic of great interest to both family and non-family members. Determining which feeding method to use involves interacting social, psychological, emotional, and environmental factors [9].

Mothers in the United States (US) most often cited the following five considerations as reasons to breastfeed [9]:

  1. Infant health benefits

  2. Naturalness of breastfeeding

  3. Facilitating infant bonding

  4. Convenience

  5. Maternal health benefits

Conversely, the chief factors cited as reasons to formula-feed were [9]:

  1. Father’s objections

  2. Fear that the baby would receive insufficient nourishment

  3. Career/job demands

  4. Physical discomfort of breastfeeding

  5. The belief that lactation adversely affects breast appearance

Although the vast majority of mothers now acknowledge that “breast is best” for their child, there are a number of psychological variables that impact a women’s decision to breastfeed. This section discusses the barriers to breastfeeding mother’s face, which range from societal stigma to their partners fears that breastfeeding will cause the breasts to sag.

8.4.1 Societal Pressures

Although breastfeeding is receiving increasing societal recognition and support in most countries around the world, there are often social costs. For instance, babies need to be fed while mothers are out in public, and mothers in many western countries report feeling awkward or embarrassed about breastfeeding in public. Currently, in the US, breastfeeding in public is illegal in five states. In Missouri, low-income pregnant women reported feeling that it was less acceptable to breastfeed in public than in the presence of visitors in one’s home, but that attempts to preserve modesty by covering the breasts should be made in both circumstances [102]. Mothers also report feeling vulnerable and prone to negative feedback when breastfeeding in public [103]. Mothers embedded in cultures stigmatising breastfeeding may confront ongoing pressure to use formula in public, lack confidence in their decision to breastfeed, and feel ashamed to breastfeed in the company of others [104].

These uncomfortable social perceptions can not only deter breastfeeding in public, but also undermine breastfeeding mothers at work. For example, breastfeeders were evaluated as both less competent and less likely to be hired in a hypothetical job search in comparison to women without children or non-breastfeeding mothers [105]. Remarkably, the negative effects of breastfeeding were perceived by raters to be as deleterious to professional success as to deciding to purposefully sexualise one’s breasts, and this sentiment was shared by both men and women [105].

Much of the taboo surrounding breastfeeding in public appears related to assumptions that bare breasts are sexually evocative or indecent [106]. The sight of a breastfeeding mother is regarded as obscene in societies where the breast is primarily regarded as sexual. Albeit an anecdotal illustration, Facebook prohibited users from posting images of breastfeeding mothers on the grounds that such images violated their decency code [107].

The extent to which breastfeeding is socially taboo, tolerated, or encouraged varies not only geographically but also by ethnicity [108]. Immigrants from societies in which breastfeeding is the norm demonstrate higher breastfeeding rates than the native population. Thus, Black immigrants from West Indian societies where breastfeeding is typical are more likely to express the intention to breastfeed exclusively than African American women [109]. The influence of prior culture on immigrant mothers appears to diminish with time; length of residence in the US was negatively correlated with initiation of breastfeeding in Puerto Rican mothers [110].

Societies also substantially vary in attitudes regarding the normal age of weaning, and mothers who transgress these expectations can suffer negative social consequences. For example, many mothers in western countries who breastfeed longer than the first few months of their child’s life report adverse social feedback [111]. In the US, approximately one third of mothers who breastfed for longer than 6 months reported perceiving negative social feedback about their breastfeeding practices [111]. This number climbs to three fifths among mothers breastfeeding for 2 years. The US and most western nations deviate from what may be considered to be the normal human breastfeeding duration. Mothers in traditional societies typically breastfeed for an average of approximately 2.5 years [112]. While there are potential social and interpersonal costs associated with breastfeeding, it is also important to acknowledge that there are also social costs associated with formula feeding [113].

Due to the consensus by health professionals that breast milk is the ideal source of nutrition for infants, mothers often face enormous pressure to breastfeed. Mothers who cannot or chose not to breastfeed fear they will be labelled as “bad mothers” by health professionals, family members, or other mothers in their communities [114]. New mothers report that where the expectations of others do not match their child feeding decisions, they can feel palpable guilt, self-doubt and confusion [115]. There have even been reports that guilt and shame associated with breastfeeding failure in mothers who intended to breastfeed can be a precursor to postpartum depression [115].

Whether a mother breast or formula feeds is often framed by academics and health care professionals as a purely personal choice made by the mother. In reality, many mothers desperately want to breastfeed, but are unable to meet their breastfeeding goals for a variety of reasons unrelated to choice. Although approximately 96% of mothers can physically lactate [116], mothers who do not receive proper breastfeeding education and professional lactation support may produce insufficient milk to nourish their infant. Women lacking access to skilled breastfeeding professionals are much more likely to experience painful breast infections (e.g., mastitis), engorgement, or cracked and bleeding nipples [3]. Additionally, many workplaces deny mothers the physical space necessary to pump and store their milk, and fail to provide convenient or flexible breaks to express milk by pump. In these circumstances, mothers have to work to financially support their child’s needs. In the US, there is also evidence that women of some racial and ethnic groups are less likely to receive essential breastfeeding support while in hospital. African American mothers are nine-times more likely to be given formula while in hospital than white mothers, and this practice explains much of the shorter duration of breastfeeding observed in African American mothers compared to white mothers [117]. These examples highlight the role that structural barriers to breastfeeding play in mothers’ feeding behaviours. No amount of pressure or guilt associated with breastfeeding will help mothers surmount these very real breastfeeding hurdles. Therefore, while educating mothers about the benefits of breastfeeding is essential, health care professionals must be sensitive in their approach and recognise that breastfeeding may not be possible or practical for women in certain circumstances.

Research tells us that educating mothers alone is not sufficient to bring about breastfeeding promotion. Education efforts targeted towards partners and families, and social support networks must also be part of any comprehensive breastfeeding promotion programme. Societal shifts in the value of infant health and the right to breastfeed are also necessary to bring about regulations that mandate employers to provide the resources for mothers to both work full time and breastfeed.

8.4.2 The Mother’s Partner

Mothers who deliberate over whether to breastfeed often consider the potential effects on their personal relationships. Breastfeeding is an intimate experience shared between a mother and baby, leaving some partners feeling excluded. Some fathers report feeling that their partner’s breastfeeding activities interfere with their own ability to bond with the baby [118], and even fathers who encourage breastfeeding sometimes acknowledge feelings of jealousy [119]. Qualitative insights from interviews indicate that such feelings can delay fathers’ inclinations to actively develop a relationship with the baby until after weaning [120]. Feelings of exclusion related to breastfeeding may generalise to include families in which two women co-parent, but only one breastfeeds.

Such negative partner reactions can sometimes be ameliorated if breastfeeding is reframed as a joint effort, if non-breastfeeding parents are provided better education about the benefits of breastfeeding, and by highlighting opportunities for non-breastfeeding parents to participate in other supportive activities while breastfeeding occurs, such as entertaining visitors [120]. Likewise, in families using a breast-pump to express milk, non-breastfeeding parents can feed breast milk to the child.

The impact of breastfeeding on mothers’ sexuality can also decrease partner support for breastfeeding [119]. Breastfeeding can diminish sexual desire in mothers, and cause vaginal dryness and painful sex [121] by lowering oestrogen levels early after birth [7]. Consistent with this early suppression of oestrogen, breastfeeders report experiencing greater vaginal pain during intercourse at 3 months after giving birth but not at 6 months [122]. In convergent evidence, breastfeeding at 3 months following birth predicts reduced reported frequency of intercourse, sexual satisfaction, and desire for sex in comparison to formula-feeding at this time point, with no difference between the two groups by 6 months post-birth [123]. While it seems that breastfeeding mothers experience diminished sexuality for the few months postpartum, the reduction is not large and, for most, has no major effect on their sexual relationship with their partner [124].

A common reason for women choosing not to breastfeed is the belief that it will adversely affect breast appearance [9]. Partners also worry about this effect, leading some to discourage their partners from breastfeeding [118]. These concerns are not supported by empirical evidence. A study of 93 women seeking plastic surgery to improve the shape of their breasts found no significant relationship between ratings of breast ptosis (drooping or sagging) and breastfeeding initiation or duration [125]. The notion that breastfeeding makes breasts sag likely comes from the fact that pregnancy leads to changes in breast tissue. This study also found that number of pregnancies, age, body mass index, larger pre-pregnancy bra cup size, and smoking history were positively related to breast ptosis. Similarly, a prospective Italian study found that mothers frequently reported changes in the size and shape of their breasts after childbirth, but these changes were not different as a function of infant feeding behaviours [126].

8.4.3 Mental Health Barriers

There is overwhelming evidence that women with depression in pregnancy or in the first weeks postpartum are less likely to initiate breastfeeding and to breastfeed for shorter durations [82], [83]. Mothers with postpartum depression report experiencing breastfeeding as more difficult [127], [128], have a higher incidence of failed attempts to breastfeed [129], and perceive themselves as less capable of effectively breastfeeding [130]. For example, women who self-report depressive symptoms at 2 weeks postpartum are more likely to wean by 2 months postpartum [131]; and depressive symptoms reported 7 weeks after giving birth predict higher rates of weaning by 6 months postpartum [132]. Similar patterns seem to uphold in women with depression prior to giving birth. Expectant mothers who report depression during pregnancy are less likely to initiate breastfeeding after giving birth [133] and, in one study, weaned 2.3 months earlier than mothers without prenatal depression [87].

It seems plausible that common symptoms of depression, such as negative mood, poor self-esteem, and anxiety, could lead women with depression to perceive common breastfeeding problems (such as pain, latching, or milk insufficiency worries) as less surmountable or more serious than their non-depressed peers [90]. Likewise, anxiety can interfere with milk supply and the milk letdown reflex [134], which could lead mothers with depression to have more breastfeeding problems [135]. In addition, mothers with depression tend to be less sensitive to infant cues [136], which may lead to problems in infant latching and the establishment of breastfeeding routines.

Finally, many antidepressant and psychiatric medications are not recommended for breastfeeding mothers, prompting some women with depression or other serious mental illnesses to choose to formula feed to enable them to receive medical treatment. The mediators that underlie the association between depression and breastfeeding outcomes should be examined in future research.

Overall, research suggests that identifying and treating mothers with prenatal or postpartum depression may encourage breastfeeding. Likewise, depressed mothers may need extra support from family members and health care professionals to meet their breastfeeding goals.

8.5 Conclusions

Breastfeeding triggers a unique psychological and physiological period that has many benefits for both mother and infant. There is strong evidence that breastfeeding alters a mother’s stress physiology, bolstering the parasympathetic nervous system, leading to lower levels of self-reported stress in breastfeeding compared to formula-feeding mothers.

There is also emerging evidence linking breastfeeding to reduced risk of postpartum depression. Some studies have found that breastfeeding may have a dose-response effect on depression risk, with increased breastfeeding frequency or intensity providing mothers more protection. The relationship between breastfeeding and postpartum depression is complex as depression can also interfere with a women’s ability or motivation to breastfeed for both psychological and biological reasons.

Markedly fewer studies have directly addressed the question of whether breastfeeding promotes maternal bonding. Despite this, there is good indirect evidence indicating that breastfeeding should promote maternal bonding, foremost that showing the association between breastfeeding hormones (oxytocin and prolactin) and parenting behaviour. However, experimental studies examining breastfeeding and maternal-bonding are difficult to carry out, and correlation studies have been confounded by the fact that maternal bonding may also engender higher breastfeeding rates.

Additionally, compared to formula-feeding mothers, breastfeeding mothers have longer slow wave sleep time, greater brain activation in response to infant cues, and may have heightened defensive aggressiveness when they or their infants are threatened.

Research in infants has focused on the physical health benefits of breastfeeding, leaving many topics on the psychological impact underexplored. Breastfeeding engages the infant’s sucking reflex, triggering relaxation and decreased activity during feeding sessions. Whether breastfeeding causes greater levels of infant relaxation than bottle-feeding or pacifiers merits research attention. Studies relying on maternal reports find that breastfed babies are fussier than formula-fed infants, while large longitudinal studies report no such differences or less negative affectivity in breast fed infants.

Although data supporting a link between breastfeeding and infant temperament are generally weak, one large prospective study reported that breastfeeding for a minimum of 6 months protected children from mental health problems in adolescence. The relationship between breastfeeding and infant temperament is complicated by research showing that maternal hormones are passed from the mother to the infant through breast milk, and breast milk composition varies from mother to mother. Infants exposed to higher levels of the hormone cortisol in breast milk have more fearful temperaments than infants exposed to lower levels. There are many bioactive components in human breast milk and the combination unique to each mother may calibrate her infant’s temperament in ways that could promote greater mother-infant synchrony.

Breastfeeding promotion efforts need to be sensitive to the many psychological and social barriers to breastfeeding faced by new mothers. Socially, some mothers feel confined to their homes because they are uncomfortable breastfeeding in public. Additionally, breastfeeding becomes less likely when people close to the mother discourage breastfeeding, and where there are challenges in the workplace. Thus, while the evidence is robust that promoting breastfeeding will have psychological benefits for mothers, their children and society as a whole, the needs and individual circumstances of mothers must be respected and addressed.

Key Points

  • In mothers, breastfeeding is associated with increased maternal sensitivity, reduced reactivity to stress, enhanced slow wave sleep, and reduced risk of postpartum depression. Stress and depression in mothers can also interfere with breastfeeding.

  • For infants, breastfeeding is associated with relaxation and components in milk likely shape infant behaviour and temperament.

  • A mother’s decision to breastfeed is often heavily influenced by those closest to her, exerting both negative and positive impacts

Jennifer Hahn-Holbrook, PhD, is an Assistant Professor in Psychology at The University of California, Merced and an internationally recognised expert on the psychological impacts of breastfeeding on mothers and their infants. She received her PhD from Queen’s University Belfast in 2010 and then completed a postdoctoral fellowship in Health Psychology at the University of California, Los Angeles. Her research broadly explores the psychological impacts of biological changes surrounding pregnancy and breastfeeding on the etiology of mental health disorders during the postpartum period.

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