Many countries like the UK and US recommend that pregnant women take vitamin D supplements. It is quite common for women to have low levels of vitamin D during pregnancy, which can increase the risk of hypertension (high blood pressure) and pre-eclampsia.
Previous studies have found that women with low vitamin D levels have a greater risk of pre-eclampsia and some trials have found that vitamin D supplementation may have some potential benefit. But researchers are still unclear if vitamin D is a cause of pre-eclampsia.
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A team of researchers set out to investigate whether vitamin D has an effect on pregnancy-induced hypertension or pre-eclampsia. They studied a population of 7389 women — 751 with gestational hypertension and 135 with pre-eclampsia — from two large European studies.
Using a technique called Mendelian randomisation, the researchers observed whether genetic variants associated with vitamin D production and metabolism influenced the risk of hypertension and pre-eclampsia in these women. They also performed another Mendelian randomisation analysis of 3388 pre-eclampsia cases and 6059 controls.
Analysing genetic information in this way avoids some of the problems that are associated with traditional observational studies, making the results of this study less prone to unmeasured factors. Therefore, any association observed using Mendelian randomisation strengthens the results that indicate any causal relationship.
The analysis showed no evidence to support a direct effect of vitamin D levels on the risk of gestational hypertension or pre-eclampsia, suggesting that vitamin D supplements may not protect against pregnancy-induced hypertension or pre-eclampsia. But researchers warn that this study had several limitations and that further large studies are needed of women with preeclampsia or more genetic variants to really understand the role of vitamin D in pregnancy-related disorders.
Source: BMJ
