No Link Between Vitamin D and Preeclampsia, Gestational Hypertension

By Marilynn Larkin

NEW YORK (Reuters Health) - A woman's vitamin D status is unlikely to affect her risk for gestational hypertension or preeclampsia, researchers say.

Pregnant women frequently have low vitamin D levels, which some studies suggest may increase the risk of preeclampsia. Some studies have suggested that vitamin D supplementation might protect against the disorder, while others have found no benefit.

To investigate further, Dr. Maria Magnus of the University of Bristol in the UK and colleagues used Mendelian randomization to determine whether genetic variants associated with vitamin D production and metabolism might also influence the risk of both preeclampsia and gestational hypertension.

As reported online June 21 in BMJ, they studied 7,389 women (751 with gestational hypertension and 135 with preeclampsia) from two large European studies, the Avon Longitudinal Study of Parents and Children (ALSPAC) and the Generation R Study.

The team also performed an additional two-sample Mendelian randomization analysis of 3,388 preeclampsia patient and 6,059 controls.

The results of their conventional multivariable analysis showed a relative risk for preeclampsia of 1.03 per 10% decrease in 25-hydroxyvitamin D level, and 2.04 for 25-hydroxyvitamin D levels less than 25 nmol/L compared with 75 nmol/L or greater. No association was found for gestational hypertension.

Results of the Mendelian randomization analyses showed no evidence to support a causal effect of vitamin D levels on the risk of either condition.

Further Mendelian randomization studies with larger cohorts are needed, according to the authors. "In combination with adequately powered clinical trials, this could help finally establish whether vitamin D status has a role in pregnancy related hypertensive disorders."

Dr. Magnus noted in an email to Reuters Health, "We only evaluated the risk of high blood pressure and preeclampsia during pregnancy, so we can't exclude that vitamin D supplementation could be beneficial for other pregnancy outcomes."

"It is important that clinicians recommend that pregnant women eat a well-balanced and varied diet throughout their pregnancy," she concluded.

Dr. Iffath Abbasi Hoskins, Clinical Professor, Department of Obstetrics/Gynecology, NYU Langone Health in New York City, commented, "There have been prior studies suggesting that low levels of vitamin D during pregnancy are associated with increased chance of hypertensive disorders. And there have been prior studies showing that supplementing pregnant women with Vit D did not prevent hypertensive disorders."

"The authors explain the differences in how the data were collected in ALSPAC (a clinician had already determined the diagnosis) and in Generation R (the abstractor pulled out blood pressure and proteinuria levels and then defined the condition afterwards)," she told Reuters Health. "These two very different methods of identifying hypertensive disorders would result in variations in how the diagnoses were made, and thus affect the outcome being studied."

"The studies to date have mainly focused on ethnically non-diverse women (European origin), and in the real world the ethnicities and therefore the genetic makeup of the pregnant women would be far more diverse," she said by email. "Diet and supplementation would also have a variable effect on circulating/available vitamin D levels during pregnancy."

"In general, supplementation with any vitamins during pregnancy for U.S. women is usually unnecessary, because their diets are satisfactory for all vitamins and minerals," she added. "Therefore, adding prenatal vitamins or supplementing with Vit D for prevention of hypertensive disorders or for any other indications is not needed."

SOURCE: https://bit.ly/2lMis0d

BMJ 2018.

(c) Copyright Thomson Reuters 2018. Click For Restrictions - https://agency.reuters.com/en/copyright.html

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