A new study finds that women who develop a severe form of pregnancy-related high blood pressure tend to have lower blood levels of vitamin D than healthy pregnant women — raising the possibility that the vitamin plays a role in the complication.

The condition is known as early-onset severe preeclampsia, and while it arises in about 2 to 3 percent of pregnancies, it contributes to about 15 percent of preterm births in the U.S. each year.

Preeclampsia is a syndrome marked by a sudden increase in blood pressure and a buildup of protein in the urine due to stress on the kidneys. Early-onset severe preeclampsia is a particularly serious form that arises before the 34th week of pregnancy.

In the current study, researchers found that vitamin D levels were generally lower among 50 women with early severe preeclampsia compared with those of 100 healthy pregnant women. The average vitamin D level in the former group was 18 nanograms per milliliter (ng/mL), versus 32 ng/mL in the latter group.

Studies have linked relatively low vitamin D levels to higher risks of type 1 diabetes and severe asthma attacks in children and, in adults, heart disease, certain cancers and depression.

If vitamin D is involved in preeclampsia risk, Robinson told Reuters Health, then it might help explain why African American women are at greater risk of the complication than other racial groups — even when factors like income and healthcare access are taken into account.

Vitamin D is naturally synthesized in the skin when it is exposed to sunlight. This process is less efficient in people with darker skin, and studies have found that African Americans commonly have low levels of vitamin D in their blood; a recent study of U.S. teenagers, for example, found that while 14 percent overall had vitamin D deficiency — defined as less than 20 ng/mL — the same was true of half of black teens.

When Robinson and his colleagues accounted for a number of factors in preeclampsia risk — including older age, heavier body weight and African American race — vitamin D levels were independently related to the odds of early preeclampsia.

A 10 ng/mL increase in vitamin D was linked to a 63 percent reduction in the odds of the complication.

It is biologically plausible, Robinson said, that the vitamin could affect preeclampsia risk. Vitamin D acts as a hormone, and lab research has found that it may affect the regulation and function of proteins in the placenta; problems in the development of the placenta are believed to be at the roots of preeclampsia.

Right now, it’s generally recommended that pregnant women get anywhere from 200 to 400 IU of vitamin D per day; prenatal vitamins contain 400 IU.