By Tara Coffin, MEd, CLE, PhDc
The short-term health benefits of breast/chestfeeding are well established. We know human milk does wonders for a premature baby’s digestive health (Boyd et al., 2007) and helps infants to build their microbiome (Mueller et al., 2015). We have also seen an infographic or two talking vaguely about the long terms health effects of human milk -- but many of these relationships are correlations at best, where data are concerned. The bottom line is that human milk is the biological norm, but we have much to learn about the mechanisms behind its magic. Without empirical evidence, the relationship between human milk and long-term health outcomes can be difficult to describe objectively. That is where epigenetics, and a recently published study in the journal Pediatrics- Epigenetic Programming by Maternal Behavior in the Human Infant, come in.
As our interest in, and knowledge of, the human genome expands, evidence supporting associations between human milk and long-term health effects grows with it (Victora et al., 2016). Early exposures, like breast/chestfeeding, that have lasting effects are the ones that leave an imprint, or an epigenetic change. Epigenetics is the study of how the environment changes gene expression. Epigenetic changes are heritable alterations to the DNA that impact gene expression and influence long-term health outcomes (Relton et al., 2015; Gluckman et al., 2010; Godfrey et al., 2007; Waterland et al., 2007). Simply put, when people talk about the long-term effects of chronic stress, they are often talking about epigenetics. High stress equates to high levels of stress hormones, which not only raise a person’s blood pressure, but they also change the very nature of who that person is--their genome. DNA methylation is also the most commonly cited epigenetic process, with evidence supporting the idea DNA methylation may be influenced by human milk, through a variety of mechanisms (Mischke et al., 2013; Karlsson et al., 2016; Alsaweed et al., 2015; Verduci et al., 2014).
A study conducted by Lester et al. (2018) sought to dive further into the relationship between breastfeeding and epigenetic changes in infants. Lester and his team recruited a cohort of healthy, term infants and their lactating parents. The study population included parents who did breastfeed (n=21) and parents who did not breastfeed (n=21) for the first five months. Researchers measured cortisol stress reactivity, an indicator of stress, in the infant saliva. DNA samples were prepared from cheek swabs and sequenced. DNA methylation was measured by assessing an important regulatory region of the glucocorticoid receptor gene and compared to homologous regions of the rat gene (based on prior animal studies).
What the researchers found was a little bit of magic. Infants who had been breastfed had decreased DNA methylation of the glucocorticoid receptor promoter and decreased cortisol reactivity. In other words, they were less stressed. Less stress equated to fewer epigenetic changes in the promoter region involved in regulation of the hypothalamic-pituitary-adrenal and immune
A couple things to note about this study. First, the research was originally based on animal studies, where researchers measured epigenetic changes in rats that were cared for by their mothers, with offspring who were not. For this study, researchers used breastfeeding as a proxy for “maternal nurturing” activity in rodents. While undoubtedly, the milk being consumed is important, one cannot breast/chestfeed their infants, or ratlings for that matter, without a little bit of skin to skin being involved in the process. With many human milk studies, effect differentiation between skin to skin and human milk can be difficult to separate and is a confounder of sorts. In other words, how much of the stress reduction is the result of the milk itself, and how much is the result of the closeness, and skin to skin, which often accompanies time spent at the breast/chest? In any case, this study tells us one thing for certain: infants that spend time close to their lactating parent consuming human milk, display lower stress indicators, inside and out.
What can childbirth educators do with this information? Educators who cover breast/chestfeeding in class can share the results of this study and discuss ways that a parent who has chosen to bottle feed (human milk or human milk substitute) may want to consider how they could increase skin to skin time during the process. While this research does not differentiate between the benefit due to human milk and the benefit due to skin to skin, adding skin to skin to the experience of bottle feeding may confer benefits for the baby who is not breast/chestfeeding.
Note: The authors also prepared a video abstract of this work, which can be reviewed here.
Alsaweed, M., Hartmann, P. E., Geddes, D. T., & Kakulas, F. (2015). MicroRNAs in breastmilk and the lactating breast: potential immunoprotectors and developmental regulators for the infant and the mother. International journal of environmental research and public health, 12(11), 13981-14020.
Boyd, C. A., Quigley, M. A., & Brocklehurst, P. (2007). Donor breast milk versus infant formula for preterm infants: systematic review and meta-analysis. Archives of Disease in Childhood-Fetal and Neonatal Edition, 92(3), F169-F175.
Gluckman, P. D., Hanson, M. A., & Mitchell, M. D. (2010). Developmental origins of health and disease: reducing the burden of chronic disease in the next generation. Genome medicine, 2(2), 14.
Godfrey, K. M., Lillycrop, K. A., Burdge, G. C., Gluckman, P. D., & Hanson, M. A. (2007). Epigenetic mechanisms and the mismatch concept of the developmental origins of health and disease. Pediatric research, 61(5 Part 2), 5R.
Karlsson, O., Rodosthenous, R. S., Jara, C., Brennan, K. J., Wright, R. O., Baccarelli, A. A., & Wright, R. J. (2016). Detection of long non-coding RNAs in human breastmilk extracellular vesicles: Implications for early child development. Epigenetics, 11(10), 721-729.
Mischke, M., & Plösch, T. (2013). More than just a gut instinct–the potential interplay between a baby's nutrition, its gut microbiome, and the epigenome. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 304(12), R1065-R1069.
Mueller, N. T., Bakacs, E., Combellick, J., Grigoryan, Z., & Dominguez-Bello, M. G. (2015). The infant microbiome development: mom matters. Trends in molecular medicine, 21(2), 109-117.
Relton, C. L., Hartwig, F. P., & Davey Smith, G. (2015). From stem cells to the law courts: DNA methylation, the forensic epigenome and the possibility of a biosocial archive.
Waterland, R. A., & Michels, K. B. (2007). Epigenetic epidemiology of the developmental origins hypothesis. Annu. Rev. Nutr., 27, 363-388.
Verduci, E., Banderali, G., Barberi, S., Radaelli, G., Lops, A., Betti, F., ... & Giovannini, M. (2014). Epigenetic effects of human breast milk. Nutrients, 6(4), 1711-1724.
Victora, C. G., Bahl, R., Barros, A. J., França, G. V., Horton, S., Krasevec, J., ... & Group, T. L. B. S. (2016). Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect. The Lancet, 387(10017), 475-490.
About Tara Coffin
Tara Coffin MEd, CLE, PhDc, is a mom, a lactation educator, and a public health researcher. She studies research dissemination in the arena of genetics and maternal and child health issues, with a focus on connecting the community with meaningful health research. With experience with educational technology, she is passionate about improving public health research dissemination and education in the virtual setting. Tara blogs about issues related to epigenetics, lactation, and public health at Milk and Genes.