More than 10,000 pregnant women took part in the National Institutes of Health-funded trial, designed to determine if average-risk women could lower their risk of developing preeclampsia by taking vitamin C and E supplements starting early in pregnancy.
Several small studies reported in the 1990s suggested a role for vitamin C and E in the prevention of preeclampsia and other pregnancy-related high blood pressure disorders, but the large trial failed to show any benefit.
The findings appear in the April 8 issue of the New England Journal of Medicine.
“The study results effectively rule out vitamin C and E supplements as a means to prevent the hypertensive disorders during pregnancy,” Alan Guttmacher, MD, of the National Institute of Child Health and Human Development (NICHD), says in a news release.
Preeclampsia Endangers Mother, Baby
The condition typically occurs after the 20th week of pregnancy, but it can develop earlier.
The cure for preeclampsia is delivery, and there is no proven way to prevent the disorder.
The causes of pregnancy-related hypertension are poorly understood, but one theory suggests that damage from molecules known as free radicals plays a role. Free radicals occur as a byproduct when the body uses oxygen.
Antioxidants like vitamins C and E interfere with free radicals and are thought to reduce free radical damage.
The Study Findings
In the newly published study, all the enrolled women were delivering for the first time.
Study co-author Catherine Y. Spong, MD, tells WebMD that first-time moms have a greater risk for preeclampsia than women who have had previous deliveries.
All the participants were considered healthy at enrollment, with no evidence high blood pressure or protein in the urine. And all were enrolled no later than their 15th week of pregnancy.
About 5,000 women were randomly assigned to take 1,000 milligrams of vitamin C and 400 IU of vitamin E daily for the rest of their pregnancy, or about 10 times the amount of C and E in the typical prenatal vitamin.
The remaining 5,000 took placebo capsules that looked exactly like the vitamins. Neither the women nor the researchers knew which treatment was being given while the trial was going on.
After all the women had delivered, the researchers reported no significant difference in preeclampsia, other high blood pressure disorders, or adverse birth outcomes between the vitamin- and placebo-treated groups.
The findings make it clear that high doses of vitamins C and E have little impact on hypertension risk during pregnancy, but this does not mean pregnant women should not take prenatal vitamins, Spong says.
“Women who want to reduce their preeclampsia risk should not be taking additional doses of vitamins C and E,” Spong says. “But women should eat a well-balanced diet when they are pregnant and they should take a prenatal vitamin.”