Using preserved blood samples of pregnant women, researchers have found that low vitamin D levels are associated with an increased risk for severe preeclampsia, a serious and sometimes fatal disorder of pregnancy.

Preeclampsia is characterized by high blood pressure and excess protein in the urine.

The study, published online in Epidemiology, used 3,703 blood samples taken between 1959 and 1966 from women at an average 21 weeks’ gestation. More than half of the women had vitamin D levels lower than 50 nanomoles per liter, which the National Institutes of Health considers inadequate for overall health, and 717 had mild or severe preeclampsia.

There was no association of vitamin D level with mild preeclampsia. But after controlling for body mass index, race, socioeconomic status and other factors, they found that women with vitamin D levels higher than 50 had a 40 percent reduction in relative risk for severe preeclampsia compared with those with levels under 50.

“Severe preeclampsia is rare,” said the lead author, Lisa M. Bodnar, an associate professor of epidemiology at the University of Pittsburgh. “And we can’t determine whether low vitamin D causes it. Women should not run out to the drugstore and buy vitamin D supplements. If you’re concerned, you should talk to your health care provider and continue to take your prenatal vitamins.”