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Objective—Breastfeeding is linked to lower rates of childhood obesity. Human milk contains cortisol, known to regulate glucose storage and metabolism. We aimed to test the hypothesis that early exposure to cortisol in human breast milk helps to modulate infant BMI trajectories over the first two years of life.

Methods—Growth curve modeling was used to examine whether infant exposure to cortisol in human milk at 3 months predicted changes in child body mass index percentile (BMIP) at 6, 12, and 24 months of age in 51 breastfeeding mother-child pairs.

Results—Infants exposed to higher milk cortisol levels at 3 months were less likely to exhibit BMIP gains over the first 2 years of life, compared to infants exposed to lower milk cortisol. By age 2, infants exposed to higher milk cortisol levels had lower BMIPs then infants exposed to lower milk cortisol. Milk cortisol was a stronger predictor of BMIP change in girls than boys.

Conclusions—Cortisol exposure through human milk may help to program metabolic functioning and childhood obesity risk. Further, because infant formula contains only trace amounts of glucocorticoids, this finding represents a novel biological pathway through which breastfeeding may protect against later obesity.


This is a pre-copy-editing, author-produced PDF of an article accepted for publication in Obesity, volume 24, issue 12, in 2016 following peer review. The definitive publisher-authenticated version is available online at DOI: 10.1002/oby.21682.


Obesity Society



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