Neuroscience Shows Breastfeeding is not Just Milk*
By Kathleen Kendall-Tackett
Breastfeeding is one important way to decrease early toxic stress. Recent studies have shown that breastfeeding increases babies’ physical and mental well-being, and these effects go well beyond the composition of the milk. Maternal responsiveness is key to understanding these long-term effects. When mothers consistently respond to their babies’ cues, they set the stage for lifelong resiliency in their offspring. And responsiveness is built into the breastfeeding relationship. We see this reflected in children’s mental health.
In one study of 2,900 mother-infant pairs, breastfeeding for one year was associated with better child mental health at every age up to age 14 (Oddy et al., 2009). Longer duration of breastfeeding was associated with better child mental health at every assessment point.
Maternal depression has a well-documented negative effect on babies and children. It is harmful because it impairs mothers’ ability to be responsive to their babies. Depressed mothers tend to disengage from their babies, and fail to respond to their cues. Babies experience this as highly stressful, and there can be lifelong effects from being raised by a chronically depressed mother or father (Field, Diego, & Hernandez-Reif, 2009; Kendall-Tackett, 2002, 2010; Weissman, 2006).
Edward Tronick‘s ‘Still-Face Mother’ experiments are an analogue of what happens with maternal depression. You can see the effects of not responding in these compelling videos.
These effects are long lasting. A 20-year follow-up of children of depressed parents compared them with a matched group of adult children whose parents had no psychiatric illness. The adult children of depressed parents had three times the rate of major depression, anxiety disorders, and substance abuse compared to adult children of non-depressed parents.
For many years, feeding method was not included in studies of maternal depression. In fact, for years, professionals who specialized in perinatal mental health believed that breastfeeding was actually a risk factor for postpartum depression. Fortunately, we now have evidence that indicates that exclusively breastfeeding mothers are at lower risk for depression. Indeed, breastfeeding is protective of maternal mental health (Dennis & McQueen, 2009; Groer & Davis, 2006; Kendall-Tackett, Cong, & Hale, 2011).
One reason why breastfeeding lowers depression risk is its impact on sleep. On every parameter of sleep, exclusively breastfeeding mothers fare better than their mixed- or formula-feeding counterparts:
- total length of sleep
- minutes to get to sleep
- percentage of slow-wave sleep
- daytime fatigue
- perceived physical health
Our study of 6,410 mothers indicated that exclusively breastfeeding mothers were significantly better on every sleep measure compared to their mixed- and formula-feeding counterparts. Surprisingly, there was no significant difference between the mixed- and formula-feeding mothers (Kendall-Tackett et al., 2011). In other words, exclusive breastfeeding is a different physiological experience than mixed feeding. When mothers supplement with formula, they lose the physiological benefit of breastfeeding on their sleep.
Protection and responsivity
One study also found that breastfeeding protects babies when their mothers are depressed. This study compared four groups of mothers: mothers who were either depressed (breast or formula-feeding) or non-depressed (breast or formula-feeding). The measure was the babies’ EEG (electroencephalogram) patterns (abnormal patterns were a symptom of depression in the infants). The babies of depressed, breastfeeding mothers had normal EEG patterns compared to the babies of depressed, formula-feeding mothers (Jones, McFall, & Diego, 2004). In other words, breastfeeding protected the babies from the harmful effects of their mothers’ depression. The reason for this finding comes down to maternal responsivity. The researchers discovered that the depressed, breastfeeding mothers did not disengage from their babies. They couldn’t. The breastfeeding mothers looked at, touched, and made eye contact with their babies more than the mothers who were not breastfeeding. And that was enough to make a difference.
Cycle of violence
Mothers with a history of childhood abuse often feel as though they do not have the tools they need to parent their own children successfully. They may wonder whether they will perpetuate the cycle of violence.
Impaired sleep can be an important trigger to the intergenerational transmission of abuse. Babies of mothers with depression or PTSD are more likely to have sleep difficulties, possibly because of their exposure in utero to their mothers’ elevated stress hormones (Field, Diego, & Hernandez-Reif, 2006; Field et al., 2007). And a recent study found that for women with PTSD and a history of childhood abuse, infant sleep difficulties and maternal depression impaired mother-infant bonding and increased the risk of intergenerational transmission of trauma (Hairston et al., 2011). But there’s a different picture if the mother breastfeeds.
In Strathearn et al’s (2009) 15-year longitudinal study of 7,223 Australian mother-infant pairs, breastfeeding substantially lowered the risk of maternal-perpetrated child maltreatment. Non-breastfeeding mothers were 2.6 times more likely to be physically abusive, and 3.8 times more likely to neglect their children compared to breastfeeding mothers.
The results of our 2013 study may help explain why this is so. In our sample of 6,410 new mothers, 994 women reported previous sexual assault. As predicted, sexual assault had a pervasive, negative effect on mothers’ sleep, physical well-being, and mental health. The sexually assaulted mothers’ sleep was poor, they were more tired, they were more anxious and angry, and had more depression. But when we added feeding method to our analyses, we found that breastfeeding attenuated the effects of sexual assault and downregulated the stress response. This effect was only for exclusively breastfeeding women (Kendall-Tackett, Cong, & Hale, 2013). Anger, in particular, was lessened and this might explain Strathearn’s findings cited above. Also, lower rates of depression improve maternal responsiveness, which is protective.
Attachment and long-term health
We can also examine the impact of security of mother-infant attachment and its effects on long-term health. In an article written shortly before the end of their lives, attachment pioneers Mary Ainsworth and John Bowlby noted that maternal (or caregiver) responsivity was key to creating a secure attachment in infants. Ainsworth developed the primary measure of attachment in infants: The Strange Situation.
The Strange Situation has been used in thousands of studies all over the world. Secure attachment on this measure is a great predictor of child mental and physical health. And responsiveness is key. When babies are not responded to consistently, they develop insecure attachments, and that has long-term implications for health, as a recent 32-year longitudinal study of 163 people found (Puig, Englund, Simpson, & Collins, 2013). Participants in this study were followed from birth to age 32. At 12 to 18 months, they were assessed via the Strange Situation. Those with insecure attachments had significantly more inflammation-based illnesses at age 32 than those who had secure attachments. These findings are likely due to the chronic activation of the inflammatory response system in those with insecure attachments.
In summary, the results from these studies demonstrate that breastfeeding has a much larger role to play in maintaining physical and mental health than we have previously believed.
Because breastfeeding increases maternal responsivity, it makes the day-to-day experience of mothering more tolerable. And it increases the chances that the babies will be securely attached. Breastfeeding is so much more than just a method of feeding. It’s a way of caring for a baby that will provide a lifetime’s worth of good health because it provides a way for mothers to connect with their babies—even if they did not experience that kind of care themselves.
In short, breastfeeding can make the world a happier and healthier place, one mother and baby at a time. It’s not just the milk.