High-dose vitamin C, E may increase preeclampsia risk: new study reverses antioxidant findings.(Obstetrics)

TORONTO -- High-dose antioxidant supplementation may be harmful in pregnant women at risk for preeclampsia, according to a study presented at the annual meeting of the Society for Gynecologic Investigation.

The study, comparing placebo with high daily doses of vitamins C (1,000 mg) and E (400 IU) in high-risk women, suggested that high doses of these vitamins conveyed no protective effect against preeclampsia. In fact, these large doses of the two antioxidants were associated with a greater risk of low birth weight, gestational hypertension, and an arterial cord pH less than 7, reported Lucilla Poston, Ph.D., lead author and professor of fetal health at Guy's, King's, and St. Thomas's School of Medicine in London.

The study, fast-tracked to the Lancet (published online March 30, doi:10.1016/S01406736[06]684 33-X), should not be interpreted as evidence against regular prenatal vitamins, which include much lower doses of antioxidants, Dr. Poston said in an interview: "There's no suggestion that women taking pregnancy vitamins had any adverse effects."

This is the first study to suggest a risk of high-dose antioxidants in pregnancy, and contrasts with previous work by the same group of investigators that suggested a protective effect of supplementation (Lancet 1999; 354:810-6).

"It's quite possible that our previous findings were an error as a result of our small numbers," Dr. Poston said, explaining that the previous study included only 160 women, with an 8% rate of preeclampsia.

She said although it has long been accepted that preeclampsia is associated with oxidative stress, her results suggest that rather than being the cause, oxidative stress may simply be a consequence of the condition. "I'm afraid to say that oxidative stress is probably an innocent bystander in preeclampsia as a result of the disease process," she noted.

This concept is consistent with mainstream cardiology research, she said. "There is overwhelming evidence that atherosclerosis and other cardiovascular complications are associated with oxidative stress, but when people have been supplemented with antioxidants there has been no effect on mortality or morbidity."