New York: Despite hopes that high doses of vitamins C and E might lower a woman`s risk of developing a pregnancy complication marked by high blood pressure, a new analysis of the evidence to date finds no benefit.
After reviewing nine studies including nearly 20,000 women, researchers found that women taking 1,000 milligrams of vitamin C and 400 IU of vitamin E - much higher doses than in most prenatal multivitamins - were no less likely to develop the potentially deadly pregnancy complication known as preeclampsia.
Instead, they saw that women given extra doses of C and E had a higher risk of certain other pregnancy complications.
Most doctors do not suggest women concerned about their risk of preeclampsia take these vitamins, and with good reason, study author Dr. Sonia S. Hassan of Wayne State University told Reuters Health. "We are not routinely recommending the use of vitamin C and E, due to the findings of this systematic analysis," she said.
Indeed, this is not the first study to cast doubt on vitamins` ability to curb preeclampsia. Last year, a 4-1/2-year study of nearly 5,000 women found those taking very high doses of vitamins C and E were 10 percent more likely to develop high blood pressure during pregnancy than volunteers taking placebo pills.
Preeclampsia, which is characterized by high blood pressure, protein in the urine and swelling, occurs in about 5 percent of American pregnancies every year. If left untreated, it can lead to severe - and sometimes fatal - complications for the woman and baby.
Some past studies have found a connection between vitamin C deficiency and an elevated risk of preterm birth, including those caused by what`s known as premature rupture of membranes -- where a woman`s "water breaks" before the pregnancy has reached full-term and labor has begun.
Vitamin C has been thought to play a role in maintaining the placenta and the membranes that surround the fetus during pregnancy, possibly by limiting so-called oxidative stress -- vitamins C and E are both "antioxidants."
So researchers have been studying whether they might help lower the risk of not only preterm birth but also preeclampsia.
However, the current study - in which Hassan and her colleagues combined results from nine studies including 19,810 pregnant women - found that 9.6 percent of women overall developed preeclampsia, regardless of whether they received extra doses of C and E or a placebo drug.
It`s not clear why taking antioxidants doesn`t reduce women`s risk, said Hassan, who is also based at the Perinatology Research Branch at the Eunice Kennedy Shriver National Institute of Child Health and Human Development, along with her co-authors Dr. Agustín Conde-Agudelo and Dr. Roberto Romero. "It is likely that although oxidative stress seems to play a major role in the disease of preeclampsia, it may not play a major role in the pathway that leads to preeclampsia."
In addition, those taking higher doses of vitamins C and E were more likely to develop high blood pressure without the protein in urine and other hallmarks of preeclampsia, and to experience a premature rupture of membranes.
Women given extra C and E did, however, have a lower risk of abruptio placentae, in which the placenta detaches from the uterine wall, the authors report in the American Journal of Obstetrics & Gynecology.
This is an interesting result, Hassan said in an email. "The finding of the decreased risk of abruptio placentae in women receiving vitamins C and E certainly may provide some insight into potential causes of abruptio placentae and can guide areas of future research."
More than 10 years ago, Dr. Lucy Chappell at King`s College London co-authored a study suggesting extra vitamin C and E could help prevent preeclampsia, but large studies conducted since have convinced her otherwise, Chappell told Reuters Health. "These findings should persuade women that they should not take vitamins C and E at these high doses."
Chappell explained in an email that her study was small, and therefore the results may have been due to a "chance statistical finding." Since the results fit all the biological theories, however, they were "jumped on with gusto," she said. However, "many initial promising studies turn out to be less so when repeated in larger numbers."