Vitamin D and risk of pregnancy related hypertensive disorders: mendelian randomisation study

BMJ. 2018 Jun 20;361:k2167. doi: 10.1136/bmj.k2167.

Abstract

Objective: To use mendelian randomisation to investigate whether 25-hydroxyvitamin D concentration has a causal effect on gestational hypertension or pre-eclampsia.

Design: One and two sample mendelian randomisation analyses.

Setting: 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).

Participants: 7389 women in a one sample mendelian randomisation analysis (751 with gestational hypertension and 135 with pre-eclampsia), and 3388 pre-eclampsia cases and 6059 controls in a two sample mendelian randomisation analysis.

Exposures: Single nucleotide polymorphisms in genes associated with vitamin D synthesis (rs10741657 and rs12785878) and metabolism (rs6013897 and rs2282679) were used as instrumental variables.

Main outcome measures: Gestational hypertension and pre-eclampsia defined according to the International Society for the Study of Hypertension in Pregnancy.

Results: In the conventional multivariable analysis, the relative risk for pre-eclampsia was 1.03 (95% confidence interval 1.00 to 1.07) per 10% decrease in 25-hydroxyvitamin D level, and 2.04 (1.02 to 4.07) for 25-hydroxyvitamin D levels <25 nmol/L compared with ≥75 nmol/L. No association was found for gestational hypertension. The one sample mendelian randomisation analysis using the total genetic risk score as an instrument did not provide strong evidence of a linear effect of 25-hydroxyvitamin D on the risk of gestational hypertension or pre-eclampsia: odds ratio 0.90 (95% confidence interval 0.78 to 1.03) and 1.19 (0.92 to 1.52) per 10% decrease, respectively. The two sample mendelian randomisation estimate gave an odds ratio for pre-eclampsia of 0.98 (0.89 to 1.07) per 10% decrease in 25-hydroxyvitamin D level, an odds ratio of 0.96 (0.80 to 1.15) per unit increase in the log(odds) of 25-hydroxyvitamin D level <75 nmol/L, and an odds ratio of 0.93 (0.73 to 1.19) per unit increase in the log(odds) of 25-hydroxyvitamin D levels <50 nmol/L.

Conclusions: No strong evidence was found to support a causal effect of vitamin D status on gestational hypertension or pre-eclampsia. Future mendelian randomisation studies with a larger number of women with pre-eclampsia or more genetic instruments that would increase the proportion of 25-hydroxyvitamin D levels explained by the instrument are needed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Case-Control Studies
  • Female
  • Genetic Predisposition to Disease
  • Humans
  • Hypertension, Pregnancy-Induced / etiology*
  • Longitudinal Studies
  • Mendelian Randomization Analysis
  • Multivariate Analysis
  • Pre-Eclampsia
  • Pregnancy
  • Risk Factors
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D / genetics
  • Vitamin D Deficiency / complications*
  • Young Adult

Substances

  • Vitamin D
  • 25-hydroxyvitamin D