Breastfed Babies Bounce Back Better (or: Of Mice & Moms Redux)

No sooner had I noted that mouse pups seem to handle stress better when near their mothers than I found a study of some 9000 British kids showing that breastfeeding seems to make kids more resilient to stress even well after they've stopped breastfeeding. As the press release puts it,

Breastfed babies cope better with stress in later life than bottle fed babies, suggests research published ahead of print in the Archives of Disease in Childhood

The findings are based on almost 9000 children, who were part of the 1970 British Cohort Study, which regularly monitors a sample of the British population from birth onwards.

Relevant information was obtained at the children's birth, and at the ages of 5 and 10 years, from midwives and health visitors, parents, and teachers. This included how much the child weighed at birth and whether s/he was breastfed.

It also included factors that might influence or be linked with a child's reactions to stress and coping mechanisms, including maternal depression, parental education levels, their social class, and smoking.

When the children were 10 years old, their teachers were also asked to rate the anxiety of their pupils on a scale of zero to 50, while parents were interviewed about major family disruption, including divorce or separation, which had occurred when their child was between 5 and 10 years of age.

Unsurprisingly, when all the data were analysed, the findings pointed to a greater likelihood of high anxiety among children whose parents had divorced or separated. But children who had been breastfed were significantly less anxious than their peers who had not been breastfed. Breastfed children [of divorced parents] were almost twice as likely to be highly anxious, while children who had been bottle fed were over 9 times as likely to be highly anxious about parental divorce/separation.

A ninefold increase instead of a twofold increase; that's a remarkable jump in vulnerability among the non-breastfed. The breastfed kids, in short, were about 1/4 as vulnerable as the nonbreastfed.

What about breastfeeding might explain such resilience? The researchers didn't want to guess. Possibly breastfeeding gives some direct physiological benefit -- the milk itself contributes physiologically, say, in roughly the way that the antibodies in mother's milk make kids more resistant to infection. Goodness knows, breastfeeding gives so many other benefits, this wouldn't surprise me. On the other hand, the protective effect might simply come from because breastfeeding creates tighter bonds with the mothers, inspiring higher levels of maternal care.

Animal studies, however, have shown that physical contact between mother and baby during the first few days of life bolsters neural and hormonal pathways important in stress responses, and that deprivation of maternal care creates hypersensitive stress systems. Moreover, as a good (if somewhat aging) research summary at NIMH describes, mere separation of rat pups from their mothers for 3 hours a day caused the mothers to give those pups less care, and the pups grew up excessively sensitive to stress all their lives; another paper finds such deprivation increases cell death in the pup's brain. Other studies, however, have shown that some of this deprivation effect can be reversed with some TLC -- or as one such paper put it, "tactile stimulation and feeding"; so it may well be that you can make up for a lack of breastfeeding with plenty of other TLC. (If you're really into this stuff, see this paper by Fleming et alia at U Toronto, "Mothering Begets Mothering," for how maternal care or deprivation in rats gets passed down through generations.)

I certainly don't want to put the onus on moms, who get enough grief; the abundance of evidence about maternal deprivation exists partly because it's easy, experimentally, to deprive baby animals of their mothers and study the results. At any rate, if there's clearly a point here about the importance of maternal care, there's also a broader point about how early experience can affect later vulnerability to stress. At the same time, genetic studies are showing that such vulnerability also depends on genetic make-up, as in this 2000 paper with the straightforward title, "The Long-Term Effects of Maternal Deprivation Depend on the Genetic Background.".

We're at an interesting time, it seems to me, as we begin to study the interlaced effects of experience and genes -- the so-called gene-environmnent interactions -- which toss aside the nature-nurture dichotomy and recognize life for what we naturally feel it to be: a dynamic loop in which what we are (our biology) constantly changes in response to what we experience (our environment).