Higher Dose of Vitamin D May Benefit Pregnant Women

By Sandra Avant,
November 3, 2016

Vitamin D is essential for strong bones and overall health, but the amount our bodies make from sunlight exposure and obtain from foods is not always enough, particularly for pregnant women.

U.S. Department of Agriculture (USDA) and University of California, Davis (UC Davis) scientists have found that a higher dose of vitamin D supplement during pregnancy may reduce inflammation. Their findings were published in the November 2016 issue of The Journal of Nutrition.

The research team included Charles Stephensen, with the USDA-Agricultural Research Service (ARS) Western Human Nutrition Research Center (WHNRC) in Davis, California; Melissa Zerofsky, a former UC Davis doctorate student; and Bryon Jacoby, a maternal fetal medicine specialist affiliated with UC Davis Medical Center. Researchers wanted to find out whether vitamin D intake levels should be higher than those common in prenatal supplements—400 international units (IU).

Severe vitamin D deficiency can contribute to osteoporosis in adults and rickets (a condition of weakened bones) in infants and children. Recent surveys also suggest that vitamin D deficiency affects up to 69 percent of American pregnant women.

Higher vitamin D levels in a person's blood may protect against certain types of cancer, strengthen the immune system, reduce diabetes risk, and play a key role in suppressing inflammation. Reducing inflammation during pregnancy is important because inflammation is associated with high blood pressure, pre-eclampsia, premature delivery and low birthweight, according to Stephensen, research leader at WHNRC's Immunity and Disease Prevention Research Unit.

In the ARS-UC Davis study, healthy women in their first trimester of pregnancy voluntarily consumed different doses of vitamin D daily. They took either a multivitamin supplement containing 400 IU vitamin D and a placebo pill, or a 400 IU vitamin D supplement and an additional 1600 IU vitamin D pill. Blood samples were analyzed for various forms of vitamin D and immune and inflammatory markers. The mothers' blood pressure and infants' birthweight were recorded.

The vitamin D dosage did not affect maternal blood pressure or infant birthweight. However, the higher daily dose, 2000 IU vitamin D, increased circulating vitamin D concentrations relative to the 400 IU per day. Higher blood vitamin D was correlated with lower circulating tumor necrosis factor-α (TNF-α), an immune substance typically associated with inflammation.

The scientists concluded that consuming 2000 IU vitamin D instead of 400 IU each day is more effective at increasing vitamin D status in pregnant women. They also found that higher levels of vitamin D increased the proportion of a specific subset of immune cells with anti-inflammatory properties that may prevent adverse effects of excess inflammation.

ARS is USDA's chief in-house scientific research agency.