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Vitamin D status linked to birth size in infants, according to new study

Posted on: October 15, 2015   by  John Cannell, MD


As I have written before, in order to facilitate a rapid birthing process in nature, human infants would need to be relatively small. Researchers believe that natural selection contributes to low birth size, as rural tribes cannot wait around for 24 hours for one of the females to give birth. Also, remember that natural selection for the size of the infant is no longer operative because of cesarean section. As someone once said, “The scalpel of the obstetrician is sharper than the scythe of natural selection.”

Labor times for other animals tend to be much shorter than for humans. For first time human moms, labor averages somewhere between 10 – 20 hours. Among other great apes (also known as the family, hominids), such as Chimpanzees, labor takes an average of two hours. Dogs go through labor in about an hour. Cattle take about two to three hours. In addition to the time in labor, human labor is extremely difficult compared to other primates.  Why?

One of the reasons may be that modern mothers are vitamin D deficient. Remember, scientists recently confirmed, in a multi-center randomized controlled trial, that human mothers need to take 6,400 IU/day to transform human breast milk into a rich source of vitamin D. This implies that pregnant women require about the same amount; however, at the most, only 1-2 % of human mothers obtain that amount of vitamin D. Certainly, human hunter-gatherers receive the equivalent of that dosage in sunshine.

One of the reasons human labor and birth is so difficult may be that when vitamin D levels are low (10 – 30 ng/ml) babies are larger, probably due to some defect, with an as yet unidentified mechansim, causing unregulated excessive growth. We also know there is a U-shaped curve for maternal vitamin D levels and birth weight. When vitamin D levels are less than 0 – 10 ng/ml, babies tend to be much smaller, probably due to substrate starvation, which simply means there is not enough D3 stored in our bodies to make all the serum 25(OH)D we need. Whereas maternal levels above 10 ng/ml but below 30 ng/ml, babies are dangerously bigger and more likely to need a C-section. Chinese researchers recently found such a U shaped curve, as has been found before, when they evaluated the relationship between vitamin D status and birth weight.

Zhu P. et al. Cord Blood 25-hydroxyvitamin D and Fetal Growth in the China-Anhui Birth Cohort Study. Sci Rep. 2015 Oct 9;5:14930.

If you look at the graphs below, you will see that U-shaped curve.

birth size graph

So were the small babies from mothers with 25(OH)D above 30 ng/ml developmentally advanced? What has not been studied, but what I predict, is that small babies (SGA) from mothers who have levels above 30 ng/ml will be less likely to develop fetal respiratory distress than will SGA babies whose mothers were severely deficient. Using the same logic, the incidence of C-section in the women with intermediate vitamin D levels should be more common than women with higher levels.

If you know anyone who is pregnant, we recommend our in-home vitamin D test kit as a pregnancy gift, the earlier in the pregnancy the better. Also, pregnant mothers should receive 5,000 – 10,000 IU/day of vitamin D3 via supplementation or safe sun exposure. We think the best supplement to take is at least 3 capsules/day (1,700 IU/capsule) of D3Plus.

1 Response to Vitamin D status linked to birth size in infants, according to new study

  1. Rebecca Oshiro

    Vitamin D undoubtedly plays a role in the birthing process. I wonder what other unknown mechanism(s) is contributing to the larger fetal size.

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