Vitamins do not reduce preeclampsia risk in women with diabetes

Taking vitamins C and E does not lower the risk of preeclampsia in women with type 1 diabetes, a study published in the Lancet and presented at the American Diabetes Association meeting in Florida, USA has found. However, these vitamins may help prevent the condition in those women low in antioxidants.

Preeclampsia can threaten the lives of mother and baby, but its causes are not known. After a small trial in 1999 suggested that vitamins C and E, which are antioxidants, might prevent the condition, researchers have been investigating their role. Several subsequent larger trials found no benefit of vitamin C and E supplementation during pregnancy.

In this new research, the Diabetes and Preeclampsia Intervention Trial (DAPIT) study group looked at women with type 1 diabetes, a condition that puts them at risk of preeclampsia and preterm delivery. Type 1 diabetes is associated with a reduction in antioxidants, so the team looked to see whether vitamins C and E could improve outcomes in women with diabetes.

The researchers examined the benefits of 1,000 mg of vitamin C and 400 IU of vitamin E in 762 pregnant women with type 1 diabetes, recruited from 25 UK antenatal clinics. Women were randomly assigned to receive vitamins or placebo every day from between 8 and 22 weeks until delivery.

The rate of preeclampsia was similar in both groups (15 per cent of women receiving vitamins vs 19 per cent of controls). However, in women with low levels of antioxidants at the start of the study, taking vitamins was associated with a significantly lower risk of preeclampsia.

The authors suggest that the vitamins might be being given too late in pregnancy to affect the pathway by which preeclampsia occurs. They also say that individual vitamin supplements may not carry the benefits of, for example, a diet high in antioxidant fruit and vegetables.

They conclude: "In principle, the notion that oxidative stress is implicated in pathogenesis of preeclampsia remains plausible, but the benefit of vitamin supplementation might be limited to women with vitamin depletion; however, this idea needs confirmation."

Contrary to previous research, this study showed no evidence that vitamin C and E supplements cause harm to mothers or babies. Antioxidant vitamins tended to reduce the risk of having a low-birthweight baby (6 per cent for the vitamin group vs 10 per cent for controls). Additionally, fewer babies were born early to women taking vitamin C.

(Source: Wellcome Trust: Lancet: June 2010)