Increased intakes of vitamin D during pregnancy may reduce the development of pre-eclampsia by about 25 percent, suggests a study with over 20,000 Norwegian women.

The risk of pre-eclampsia was 27 per cent lower in women who consumed vitamin D supplements with daily doses of 10 to 15 micrograms, compared to women who did not take supplements, according to researchers from the Norwegian Institute of Public Health.

However, a correlation between vitamin D intake and omega-3 fatty acid intake was observed, and the researchers noted that “further research is needed to disentangle the separate effects of these nutrients”.

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.

However, subsequent studies, including a study published in The New England Journal of Medicine (Vol. 354, pp. 1796-1806) and a Cochrane Systematic Review (2007, Issue 4), found that vitamins C and E had no effects on the risk of pre-eclampsia.

The new study, published in Epidemiology suggests that vitamin D supplementation may reduce the risk of developing the potentially fatal condition.

Led by Helle Margrete Meltzer, the researchers examined the relationship between vitamin D intakes during pregnancy and the risk of pre-eclampsia in 23,423 would-be first time mothers participating in the Norwegian Mother and Child Cohort Study.

The women answered a general health questionnaire at the fifteenth week of pregnancy and again at the thirtieth week, while a food frequency questionnaire was administered at week 22.

According to the Norwegian findings, women with a daily intake of between 15 and 20 micrograms of vitamin D from diet and supplements had a 24 per cent lower risk of developing pre-eclampsia compared to women who consumed less than 5 micrograms per day.

The overriding benefits were observed for vitamin D from supplements, with a daily dose of 10 to 15 micrograms linked to a 27 per cent reduction, compared to women who did not take supplements.

“These findings are consistent with other reports of a protective effect of vitamin D on pre-eclampsia development,” wrote Meltzer and her co-workers.

“However, because vitamin D intake is highly correlated with the intake of long chain omega-3 fatty acids in the Norwegian diet, further research is needed to disentangle the separate effects of these nutrients,” they concluded.

Source: Epidemiology

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August 24, 2009