Vitamin D deficiency increases the risk of life-threatening preeclampsia during pregnancy five fold, Pennsylvania researchers reported.

Some researchers have suspected that low levels of vitamin D contribute to the disorder, which is characterized by soaring blood pressure and swelling of the hands and feet, but the new study is the first to examine its role directly.

Preeclampsia affects as many as 7 percent of first pregnancies and can progress to eclampsia, which produces seizures and often fatal complications of the liver, kidneys, lungs, blood and nervous system. Eclampsia causes 15 percent of maternal deaths during pregnancy and as many as 70 percent of such deaths in developing countries.

Epidemiologist Lisa M. Bodnar and her colleagues at the University of Pittsburgh School of Health Sciences studied blood samples taken from women and newborns early in pregnancy and just before delivery. They identified 15 women who suffered preeclampsia and compared them with 220 who did not.

Although most of the women had levels of vitamin D lower than the optimum level of 80 nanomoles per liter, those who suffered preeclampsia had significantly lower levels. Women whose levels were below 37.5 nanomoles per liter had five times the risk of developing the disorder, the team reported Friday in the Journal of Clinical Endocrinology & Metabolism.

Surprisingly, "the vast majority" of the women were taking prenatal vitamins, which contain 200 to 400 international units of vitamin D.

"Experts believe you need to take 1,000 IUs per day to make a dent in increasing your levels ( of the vitamin)," Bodnar said, and "that would certainly be an appropriate recommendation for a pregnant woman. We do not suggest that will prevent preeclampsia, but ... it has a lot of potential benefits."

Preliminary results from studies under way at the Medical College of South Carolina have shown no adverse effect from consuming as much as 4,000 IUs per day, she said.