On the other hand, scientists from Northern Ireland do report that the supplements could benefit women with low antioxidant status, according to findings presented at the American Diabetes Association meeting in Florida, USA and published in The Lancet.
The findings also support the tolerability and safety of vitamin C and E supplements, with no harm to mothers or babies reported.
The study’s findings add to previous findings in non-diabetic women. A review published in 2007 in the Cochrane Database of Systematic Reviews (doi: 10.1002/14651858.CD004227.pub3) appeared to close the door on research into the use of the antioxidants to reduce the risk of pre-eclampsia.
Pre-eclampsia, affecting two to three per cent of all pregnancies, occurs when a mother's blood pressure rises to the hypertensive range, and excretion of protein in the urine becomes too high. It is estimated to be responsible for about 60,000 deaths worldwide.
It is not known why some expectant mothers develop pre-eclampsia, although oxidative stress has been proposed to play a part. The role of antioxidants to reduce oxidative stress had been supported by a small clinical trial that linked vitamin C and E intake to fewer biomarkers for pre-eclampsia for predominantly low-risk participants.
According to the researchers, women with type-1 diabetes are at high risk of pre-eclampsia and preterm delivery, linked to the increased levels of oxidative stress in these individuals.
Type-1 diabetes occurs when people are not able to produce any insulin after the cells in the pancreas have been damaged, thought to be an autoimmune response. The disease is most common among people of European descent, with around two million Europeans and North Americans affected.
Led by Professor David McCance from the Belfast’s Royal Victoria Hospital, the researchers recruited 762 pregnant women with type-1 diabetes to participate in the Diabetes and Pre-Eclampsia Intervention Trial (DAPIT).
Women were randomly assigned to receive either placebo or a daily antioxidant supplement containing 1,000 mg of vitamin C and 400 IU of vitamin E from between 8 and 22 weeks' gestation until delivery.
Similar rates of pre-eclampsia were observed in both groups, but women with low antioxidant status at the start of the study benefitted from a significantly lower risk of pre-eclampsia:
“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,” concluded the researchers.
In an accompanying editorial, Baha Sibai from the University of Cincinnati, Ohio, adds a note of caution. “The placebo group in DAPIT contained more women with previous pre-eclampsia, chronic hypertension, and nephropathy (factors that increase the rates of the above complications) than did the supplementation group,” wrote Sibai, “because the DAPIT investigators did not adjust for all the above factors in women with low antioxidant status, the conclusions for this group might not be valid.”
"The aetiology of pre-eclampsia might be multi-factorial. Some cases might be caused by immunological factors, others by dietary factors, and others because of pre-existing medical conditions, or by a combination of these factors. Therefore any single intervention is unlikely to be effective in prevention,” concluded Sibai.
Source: The Lancet
Published online ahead of print, doi: 10.1016/S0140-6736(10)60630-7
“Vitamins C and E for prevention of pre-eclampsia in women with type-1 diabetes (DAPIT): a randomised placebo-controlled trial”
Authors: D.R. McCance, V.A. Holmes, M.J.A. Maresh, C.C. Patterson, J.D. Walker, D.W.M. Pearson, I.S. Young, for the Diabetes and Pre-eclampsia Intervention Trial (DAPIT) Study Group
Editorial: The Lancet
Published online ahead of print, doi: 10.1016/S0140-6736(10)61007-0
“Vitamin C and E to prevent pre-eclampsia in diabetic women”
Author: B.M. Sibai