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As a new parent you can go no longer than 24 hours without hearing the phrase “Breast is Best.” I know this to be true because I became a parent in June of this year. In the hospital we were offered consults with lactation and had no less than six posters in our room touting the benefits of breastfeeding. As a PhD student I was intrigued by the literature behind these recommendations and eagerly spent multiple late night nursing sessions on my iPad reading the latest research. What I found were some studies finding associations with reduced risk of obesity, and others failing to find this same association (literature). Overall, it was concluded in the previous review that breastfeeding was associated with a reduced risk of obesity.

While this was great news, I could not help but question; was this association because of breastmilk or mode of delivery? Bottle feeding is typically associated with formula feeding but a growing number of women have begun pumping their breastmilk after returning to work or in cases of pre-term birth and latch issues.

Could bottle feeding breastmilk still ameliorate the risk of obesity later in life?

I was not the first person to raise this question which has been addressed here, here, here, and here. Overall the consensus seems to be that early bottle feeding, of breastmilk or formula, is associated with an increased risk for excess weight gain and poor self regulation. Exclusively feeding expressed milk is also associated with early cessation of breast-milk feeding.

So this leads to the inevitable question; what is a mother to do?

While the literature is still unclear if bottled breastmilk can fight obesity risk, it is clear the breastmilk has multiple other benefits according to the American Academy of Pediatrics and should be offered when possible. So to those mothers who pump a little, a lot, or all the time, I say pump on ladies!

Does Breastfeeding Make You Smarter?

Good nutrition has been shown to help with survival, growth, mental development, health, and well-being across one’s lifespan. Unearthing precisely what to eat to help achieve maximal benefit has been the subject of many research studies and debates, especially regarding childhood nutrition starting at an early age.

Breastfeeding has been recognized for its ability to provide infants with essential nutrients to help with growth and development. Research has shown there are many benefits associated with breastfeeding, such as building a healthy gut microbiota and increasing the bond between mother and child. The child benefits from the nutrients found in breast milk, such as docosahexaenoic acid (DHA) and arachidonic acid, omega-3 and -6 fatty acids essential for cognitive development. Somewhere down the line the notion that breastfeeding can make your baby smarter has been perpetuated. However, this has not yet been proven.

Researchers from the University College Dublin in Ireland conducted a study to investigate the impact of breastfeeding on children’s cognitive development. Around 8,000 families from the Growing Up in Ireland longitudinal infant cohort were randomly selected to participate. Data was collected when the child was 9 months old, 3 years old, and 5 years old. Questionnaires were used to measure children’s cognitive abilities, expressive vocabulary, and problem behaviors, and breastfeeding data was collected as retrospective self-report from the mothers. Propensity score matching, instrument variables, and sibling pair models were used for the analysis. The “breastfed” and “never breastfed” groups were matched based on infant, mother, and family-level factors, such as birth weight and maternal age.

Children who were breastfed scored higher on the problem-solving scale. However, after adjusting for potential confounders, this result was found to be no longer significant. This means other factors, such as socioeconomic status, could better explain the variability here. Breastfed children had lower parent-rated hyperactivity compared with controls after the adjustment, but this effect was only seen at 3 years of age. This may mean that breastfeeding helps reduce hyperactivity in the short term, but this effect was not maintained. Although the researchers found no evidence to support that breastfeeding helps improve cognitive abilities, they did note that their study did not contradict any of the medical benefits of breastfeeding. Research on breastfeeding will continue to be done and hopefully we will see more positive findings emerge in this area. For now, the current World Health Organization recommendation for breastfeeding is to exclusively breastfeed for the first 6 months of a child’s life, if you are able.

 

References:

Girard L, Doyle O, Tremblay RE. Breastfeeding, Cognitive and Noncognitive Development in Early Childhood: A Population Study. Pediatrics. 2017;139(4):e20161848. doi:10.1542/peds.2016-1848

By Corrie Whisner, PhD

I recently ran across an interesting article in the PLOS ONE journal entitled, “Holsteins Favor Heifers, Not Bulls: Biased Milk Production Programmed during Pregnancy as a Function of Fetal Sex” by Katie Hinde and colleagues at Harvard and Kansas State Universities. After the passing of International Women’s Day on March 8 and recently finishing the book Lean In by Sheryl Sandberg, I felt inspired to share Hinde’s findings and highlight the scientific side of “girl power!”

In this large retrospective analysis of dairy cow lactation records, researchers found that Holsteins produced 1.6% more milk for female versus male offspring. More interesting, is the finding that fetal sex of first-time mothers influenced milk production in subsequent pregnancies.  The advantage of having a female fetus during the first pregnancy carried over to the second pregnancy, resulting in greater milk production across both lactations regardless of whether the second fetus was male or female. The benefit of having a heifer during the first pregnancy was further documented when cows giving birth to a male in their first pregnancy showed significant increases in milk production if their second pregnancy was a female. This increase was evident when comparing data to milk production in dairy cows that gave birth to two consecutive male offspring; however, the milk production of male-female sequence mothers, did not increase to the level of female-first mothers.

According to Hinde, biologists have been interested in studying how mothers differentially allocate resources to male versus female fetuses during pregnancy. To date, little work has been done to investigate sex-biases in milk production which make this article very exciting! Reading this article definitely reminded me of the Barker Hypothesis and the earlier publication Boys Live Dangerously in the Womb, which both provide evidence for fetal programming in humans and suggest that male and female fetuses respond differently in utero to maternal cues.

Maternal milk is an ever-evolving elixir which fuels important changes throughout early development, so it isn’t hard to believe that milk production might differ between species. After reading this article I amazed to learn that mothers may allocate resources, such as milk, to the offspring sex that will receive maximal benefit. A current belief is that males from species with male-male competitive mating rituals will receive a greater investment across gestation and lactation from their mothers. Additionally, Rhesus monkeys have been found to produce energetically-dense milk, higher in fat, for their male offspring; however, female offspring received a greater milk volume which made up for the lack in energetic-density.

As research continues in this area, I wonder if we will start seeing different types of baby formula for boys and girls. Only time will tell…and to that, I say, “Let’s get MOO-ving, so we have more to talk about soon!”

References
1.    Katie Hinde, Abigail J. Carpenter, John S. Clay, Barry J. Bradford. Holsteins Favor Heifers, Not Bulls: Biased Milk Production Programmed during Pregnancy as a Function of Fetal Sex. PLoS ONE, 2014; 9 (2): e86169 DOI:10.1371/journal.pone.0086169
2.    Trivers RL, Willard DE (1973) Natural selection of parental ability to vary the sex ratio of offspring. Science 179(4068): 90–92. doi: 10.1126/science.179.4068.90
3.    Hinde K (2007) First-time macaque mothers bias milk composition in favor of sons. Curr Biol 17(22): R958–R959. doi: 10.1016/j.cub.2007.09.029
4.    Hinde K (2009) Richer milk for sons but more milk for daughters: Sex-biased investment during lactation varies with maternal life history in rhesus macaques. Am J Hum Biol 21(4): 512–519. doi: 10.1002/ajhb.20917