SATURDAY, June 26 (HealthDay News) -- Taking vitamin C and E supplements will not lower the risk of the blood pressure disorder known as preeclampsia in pregnant women with type 1 diabetes, a new study finds.

Women with diabetes are at high risk for preeclampsia (a sudden increase in the mother's blood pressure after the 20th week of pregnancy), and prior research has suggested that because type 1 diabetes is associated with increased oxidative stress and lower levels of antioxidants in the body, taking antioxidant vitamins might help.

The British study included 762 pregnant women with type 1 diabetes. They were randomly assigned to take 1000 milligrams of vitamin C and 400 international units (IU) vitamin E (379 women) or placebo (383 women) daily from between eight and 22 weeks of gestation and delivery.

The rate of preeclampsia was 15 percent in the vitamins group and 19 percent in the placebo group. However, taking vitamins seemed to significantly lower the risk of preeclampsia in women with low antioxidant status at the start of the study and appeared to reduce the risk of having a low birthweight baby (6 percent vs. 10 percent). Also, fewer women in the vitamin C group had preterm babies.

Researchers from Queen's University Belfast said the findings suggest that dietary "intervention rich in various antioxidants might have benefits that cannot be replicated by individual supplements. Alternatively, prescription of antioxidant vitamins at 8-22 weeks' gestation might be too late to affect the pathological process for most patients with diabetes."

"In principle, the notion that oxidative stress is implicated in pathogenesis of pre-eclampsia remains plausible, but the benefit of vitamin supplementation might be limited to women with vitamin depletion; however, this idea needs confirmation," they concluded.

However, in a commentary, Dr. Baha M. Sibai of the University of Cincinnati, noted that the study participants who took a placebo were more likely to have had a prior history of preeclampsia or chronic high blood pressure than women who took the vitamins. Because the researchers did not adjust for this and other factors "in women with low antioxidant status, the conclusions for this group might not be valid," he wrote.

Sibai also noted that because preeclampsia can have many causes, "any single intervention is unlikely to be effective in prevention."

The study appears online in The Lancet and is also slated for presentation Saturday at the American Diabetes Association meeting in Orlando.

More information

The U.S. National Institute of Child Health and Human Development has more about preeclampsia.