Vitamin D and Breast Milk

I’ve been wondering since my little girl was born 8 months ago, why I would need to give her a vitamin D supplement if I’m breastfeeding?  After all, human babies and human breast milk have evolved together over millions of years to be a perfect combination.  You wouldn’t expect breast milk to be lacking anything, would you?  Yet the AAP recommends all breastfed infants receive a supplement of 400IU vitamin D daily.

So, what’s the deal?

Evolution says that those who have the best adaptations will be able to reproduce the best.  Those who reproduce the best will pass on their genes, and those genes will eventually become more pronounced in the population.  So, in this context, those mothers who make the milk that provides best for a human baby will be more likely to pass on their genes (via children, grandchildren, etc).

Human breast milk only has about 25IU of vitamin D per liter.  That would require 16 liters for your baby to get the recommended amount of vitamin D per day.  Even those babies who would happily spend the day attached to his or her mother’s breast couldn’t drink that much!  Has evolution let us down?

Not exactly.  Vitamin D can also be made via exposure to sunlight and ultraviolet rays.  The concept of staying indoors and avoiding the sun all day is relatively new.  The dangers of skin cancer have forced us to wear sunscreen and protective clothing.  Back in the day, when our ancestors were out hunting/gathering/farming/doing cool ninja stuff in the sun all day, they probably had plenty of time to synthesize vitamin D.

Great news.  Evolution still loves us.  We just changed our routines faster than we changed our milk.  Case closed.

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