WEDNESDAY, March 29, 2006 (HealthDay News) -- Taking high doses of vitamin C and E supplements won't lower the risk of developing preeclampsia for pregnant women already at high risk for the condition.
In fact, taking the supplements might increase the risk of having a low birth-weight baby, according to a study published online March 30 in the journal The Lancet.
However, women taking normal multivitamins for pregnancy did not have an increased risk of low birth-weight babies or any other problems, the study found.
The findings strongly suggest that women should not take high doses of these vitamins while they're expecting.
"This was a decisive study as far as high-risk women are concerned," said Lucilla Poston, lead author of the study and director of the research division of reproductive health, endocrinology and development at King's College London. "Women should not self-dose on high-dose vitamin C and E supplements. These are available across the counter and, we suggest, are now contraindicated in pregnancy."
"These are very concerning findings," added Dr. Ashley S. Roman, assistant professor of obstetrics and gynecology at New York University School of Medicine. "There doesn't seem to be a clear indication for separate vitamin C and E supplementation right now and there are potential drawbacks."
Preeclampsia, a condition in which the expectant mother develops dangerously high blood pressure, is believed to occur in roughly 5 percent of all pregnancies, affecting 200,000 American women each year. According to the study authors, some 60,000 deaths worldwide each year are attributable to the condition.
Mothers and babies are at risk of dying, while babies are also at risk for other health problems, including blindness, cerebral palsy and mental retardation. The only cure for preeclampsia is delivering the baby, a tricky proposition if the baby is not full-term.
"The baseline problem is we don't know what causes preeclampsia," Roman said. "One of the underlying theories is that it's basically a systemic inflammatory reaction that's gone awry and the theory is that, by giving antioxidants [vitamins], you can dampen this response and thereby prevent preeclampsia."
One small, previous study conducted by the same authors had suggested that taking vitamin E and C could actually reduce the incidence of preeclampsia in pregnant women. That trial, however, was ended early. A second, even smaller study found no effect of these antioxidants on the risk of developing preeclampsia.
However, another study found that boosting the calcium intake of pregnant women with low dietary calcium can help prevent complications from preeclampsia. But while the extra calcium decreased the severity of the condition, it did not reduce the number of women who developed it.
The new trial involved a much larger group -- about 2,400 women from 25 British hospitals who were at high risk for preeclampsia. The participants were randomly assigned to receive 1,000 milligrams of vitamin C and 400 International Units (IUs) of vitamin E or a placebo daily, starting in the second trimester of pregnancy and continuing until delivery.
Although these doses were high, they were still below the maximum recommended intake for pregnant women. In the United States, the Institute of Medicine's Food and Nutrition Board recommends an upper limit of vitamin C during pregnancy at 2,000 mg per day, and of vitamin E at 1,000 mg.
The incidence of preeclampsia among study participants was similar in both groups -- 15 percent in the treatment group and 16 percent in the placebo group. The proportion of small-size-for-gestational-age babies was also similar, 21 percent versus 19 percent, respectively.
However, more low birth-weight babies were born to women taking vitamins, 28 percent versus 24 percent in the placebo group.
In addition, women receiving the supplements needed more treatment, including steroids, antihypertensive medication and magnesium sulphate. This may have been because these women had an earlier onset of preeclampsia than women in the control group. Early onset preeclampsia is usually more severe, the researchers said.
"There is no evidence that taking vitamins C and E in multivitamin preparations recommended for pregnancy is harmful," Poston said. "Indeed, our study suggested that women who were taking these multivitamins had slightly larger babies than those who were not."
The fact that the high-dose supplementation didn't work does not mean that the leading theory of preeclampsia's cause is incorrect. "It could still be the case, but just that this is not the miracle bullet," Roman said.
In the meantime, researchers in Australia and elsewhere are looking at the potential value of vitamin E and C in low-risk women, such as those who have not had previous pregnancies.
For more on preeclampsia, visit the American Academy of Family Physicians.