Women deficient in vitamin D early in their pregnancies are more likely to deliver babies with lower birth weights, University of Pittsburgh Graduate School of Public Health research reveals.
The research team discovered that mothers with levels of vitamin D in their blood of less than 0.015 parts per million (37.5 nmol/L) in their first 26 weeks of pregnancy delivered babies who weighed an average of 46 grams less than their peers. Only full-term babies - those delivered between 37 and 42 weeks of pregnancy - were included in the study.
In addition, women who were vitamin D deficient in the first trimester of pregnancy - 14 weeks or less - were twice as likely to have babies who fell in the lower 10th percentile for weight when compared to other full-term babies born in the same week of pregnancy, a condition known as "small for gestational age."
Babies born small for gestational age are at five to 10 times greater risk for death in their first month and have a higher risk of chronic diseases, such as heart disease, hypertension and type 2 diabetes, later in life.
Results from this study - one of the largest studies to examine a mother's vitamin D levels and their relationship with birth weights - show that clinical trials to determine if you can improve birth weights by giving women of reproductive age vitamin D supplements may be warranted.
Vitamin D is unique in that our bodies can make it from sunlight, though it also is in fortified foods, such as milk and orange juice, and can be taken as a supplement.
The study used a random sample of 2,146 pregnant women who participated in the Collaborative Perinatal Project, which was conducted in 12 U.S. medical centers from 1959 to 1965. The blood samples collected by the project were well-preserved and able to be tested for vitamin D levels half a century later.
"Although the blood samples were in remarkably good condition, it would be beneficial to repeat our study in a modern sample," the researcher said. "Today women smoke less, weigh more, have less sun-exposure and get more vitamin D in their foods - all things that could impact their vitamin D levels and babies' birth weights."
Maternal vitamin D deficiency could cause low birth weight by inhibiting the typical increase in calcium absorption by pregnant women, which could reduce fetal bone growth. It also could lead to a decrease in the hormones necessary to produce the glucose and fatty acids that provide for fetal energy needs.
Source: Journal of Clinical Endocrinology & Metabolism, online December 2012
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