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No evidence that vitamin D protects against gestational hypertension or pre-eclampsia

Research presented in the BMJ has concluded that there is no strong evidence that vitamin D protects against pregnancy-induced hypertension or pre-eclampsia.

Observational studies have found that women with lower levels of 25-hydroxyvitamin D are at greater risk for pre-eclampsia and some trials of vitamin D supplementation in pregnancy suggest a potential benefit. In many countries, including the United Kingdom, pregnant women are advised to take a daily dose of vitamin D. 

However, these latest findings support current WHO guidance that evidence recommending vitamin D supplements for women during pregnancy to reduce adverse pregnancy outcomes is insufficient.

The international study, led by the University of Bristol, used one- and two-sample mendelian randomisation analyses of two European pregnancy cohorts (Avon Longitudinal Study of Parents and Children, and Generation R Study), and two case-control studies (subgroup nested within the Norwegian Mother and Child Cohort Study, and the UK Genetics of Pre-eclampsia Study).

The 1-sample analysis included 7389 women (751 with gestational hypertension and 135 with pre-eclampsia), and the 2-sample analysis included 3388 pre-eclampsia cases and 6059 control patients.

In the conventional multivariable analysis, the relative risk (RR) for pre-eclampsia was 1.03 (95% CI, 1.00-1.07) per 10% decrease in 25-hydroxyvitamin D levels and 2.04 (95% CI, 1.02-4.07) for 25-hydroxyvitamin D levels <25 nmol/L compared with ≥75 nmol/L. No association was found for gestational hypertension.

The 1-sample mendelian analysis using the total genetic risk score as an instrument did not provide strong evidence of a linear effect of 10% decrease in 25-hydroxyvitamin D on the risk for gestational hypertension (OR, 0.90; 95% CI, 0.78-1.03) or preeclampsia (OR, 1.19; 95% CI, 0.92-1.52).

The 2-sample mendelian randomisation estimate gave ORs for preeclampsia of 0.98 (95% CI, 0.89-1.07) per 10% decrease in vitamin D levels, 0.96 (95% CI, 0.80-1.15) per unit increase in the log(odds) of vitamin D <75 nmol/L, and 0.93 (95% CI, 0.73-1.19) per unit increase in the log(odds) of 25-hydroxyvitamin D levels <50 nmol/L.

The authors reported that no strong evidence was found to support a causal effect of vitamin D status on gestational hypertension or pre-eclampsia but said further studies are needed.


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