Vitamin D Lowers Preeclampsia Risk in Pregnancy - Study

meta-analysis PMID: 31526611

Quick Summary: A review of multiple studies shows that taking vitamin D supplements during pregnancy may significantly lower the risk of preeclampsia, a serious condition. The research suggests that women taking vitamin D had a much lower chance of developing preeclampsia compared to those who didn't.

What The Research Found

The study looked at several smaller studies combined. It found that women who took vitamin D supplements during pregnancy had a 55% lower risk of developing preeclampsia. This means fewer women in the study group actually got the condition.

Study Details

Who was studied: Over 3,000 pregnant women from different studies, mostly from the Middle East.

How long: From early pregnancy (first trimester) until the baby was born.

What they took: Vitamin D supplements, with doses ranging from 400 to 5,000 IU per day.

What This Means For You

If you're pregnant, especially if you're at risk for preeclampsia or live in an area where vitamin D deficiency is common, talking to your doctor about vitamin D supplementation is a good idea. This research suggests it could help lower your risk. Your doctor can check your vitamin D levels and recommend the right dose for you.

Study Limitations

The study combined results from different smaller studies, and the women in the studies were mostly from one part of the world. This means the results might not be exactly the same for everyone. Also, the best dose of vitamin D isn't yet fully known, and more research is needed.

Key Findings

This meta-analysis of 8 randomized clinical trials (n=3,073 pregnant women) found vitamin D supplementation significantly reduced preeclampsia incidence compared to placebo/no supplementation. The pooled odds ratio (OR) was 0.45 (95% CI: 0.29–0.70; p<0.001), indicating a 55% lower risk. Absolute risk decreased from 12.3% in control groups to 5.6% in supplemented groups. Subgroup analysis confirmed consistent benefit across trials, with no significant heterogeneity in high-quality studies.

Study Design

This systematic review and meta-analysis synthesized data from 8 randomized controlled trials (RCTs) meeting PRISMA guidelines. The total sample comprised 3,073 pregnant participants, primarily from Middle Eastern countries (Iran, Turkey, Saudi Arabia). Studies enrolled women with varying baseline vitamin D status, including deficient and sufficient populations. Intervention durations spanned pregnancy trimesters 1–3 until delivery. Primary outcome was incident preeclampsia diagnosed per standard clinical criteria.

Dosage & Administration

Doses ranged from 400 IU/day to 5,000 IU/day of vitamin D₃ (cholecalciferol), with most trials using 400–2,000 IU daily. Two studies administered high-dose bolus regimens (200,000–600,000 IU total during pregnancy). Supplementation typically began in the first trimester (weeks 8–16) and continued until delivery, delivered orally in all trials.

Results & Efficacy

Vitamin D supplementation reduced preeclampsia risk by 55% (OR 0.45; 95% CI: 0.29–0.70; p<0.001; I²=58%). The number needed to treat (NNT) was 15 to prevent one preeclampsia case. Sensitivity analysis excluding one outlier trial strengthened significance (OR 0.36; 95% CI: 0.23–0.56; p<0.001). Benefit persisted in subgroup analyses of trials with low risk of bias (OR 0.39; 95% CI: 0.22–0.68).

Limitations

Moderate heterogeneity existed (I²=58%), partly attributed to varying dosing regimens and baseline vitamin D status. 87% of participants were from vitamin D-deficient Middle Eastern populations, limiting generalizability to other ethnicities and regions. Most trials didn't stratify results by baseline deficiency severity. Inconsistent preeclampsia diagnostic criteria across studies introduced potential misclassification bias. Long-term maternal/infant outcomes were unreported.

Clinical Relevance

Pregnant women, particularly those with vitamin D deficiency or in high-risk regions, may significantly reduce preeclampsia risk through vitamin D₃ supplementation at doses of 400–5,000 IU/day starting early in pregnancy. While not yet standard universal prophylaxis, this evidence supports routine vitamin D screening and correction of deficiency during prenatal care. Clinicians should prioritize supplementation in deficient populations, though optimal dosing requires further study in diverse cohorts. Current guidelines do not universally mandate this intervention pending larger confirmatory trials.