Researchers combined results from 29 studies involving over 74,000 pregnant women to understand if low vitamin D levels increase the risk of preeclampsia—a serious pregnancy condition involving high blood pressure. They found that women who developed preeclampsia did have lower vitamin D levels overall. However, the connection wasn’t strong enough to say with certainty that vitamin D deficiency directly causes preeclampsia. The findings suggest vitamin D may play a role, especially when measured early in pregnancy, but more research is needed before doctors can recommend vitamin D supplements specifically to prevent this condition.

The Quick Take

  • What they studied: Whether pregnant women with low vitamin D levels are more likely to develop preeclampsia (a dangerous condition with high blood pressure during pregnancy)
  • Who participated: 29 different research studies involving 74,061 pregnant women from around the world. Some studies looked at women early in pregnancy, others in the middle, and they compared those who developed preeclampsia with those who didn’t
  • Key finding: Women with preeclampsia had noticeably lower vitamin D levels than women without it. However, when researchers looked at whether vitamin D deficiency alone predicted preeclampsia, the connection wasn’t statistically proven—meaning it could partly be due to chance
  • What it means for you: If you’re pregnant or planning pregnancy, this suggests vitamin D may be important for pregnancy health, but it’s not yet proven that taking vitamin D supplements will prevent preeclampsia. Talk to your doctor about your vitamin D levels and whether supplementation is right for you

The Research Details

This was a meta-analysis, which means researchers looked at 29 existing studies and combined their results to see the bigger picture. They searched major medical databases (PubMed, Scopus, Web of Science, and Cochrane Library) through June 2023 to find all relevant studies about vitamin D and preeclampsia. All the studies they included were observational studies, meaning researchers watched and measured what happened naturally rather than randomly assigning people to take vitamin D or a placebo.

For each study, researchers extracted information about how much vitamin D pregnant women had in their blood and whether they developed preeclampsia. They then combined all this data using statistical methods to look for patterns. They also looked at subgroups—for example, studies that measured vitamin D early versus late in pregnancy—to see if timing mattered.

This approach is important because no single study had enough participants to give a definitive answer. By combining 29 studies with over 74,000 women total, researchers could spot patterns that might not be obvious in smaller studies. However, because these were observational studies (not controlled experiments), we can see associations but can’t prove that low vitamin D actually causes preeclampsia

The researchers carefully assessed how well each study was done before including it. The large number of participants (74,061) gives the findings more weight. However, the studies came from different countries with different methods of measuring vitamin D, which can make comparisons tricky. The fact that results weren’t statistically significant for vitamin D deficiency alone suggests the connection may be weaker than initially thought

What the Results Show

Women who developed preeclampsia had measurably lower vitamin D levels compared to women who didn’t develop the condition. This difference was statistically significant, meaning it’s unlikely to be due to random chance alone.

However, when researchers looked at whether having vitamin D insufficiency (low but not severely low levels) increased preeclampsia risk, the odds ratio was 1.05—essentially showing almost no increased risk. For vitamin D deficiency (very low levels), the odds ratio was 1.25, suggesting a possible 25% increased risk, but this wasn’t statistically significant either, meaning it could be due to chance.

When researchers looked at studies that measured vitamin D early or in the middle of pregnancy specifically, they found a stronger pattern suggesting vitamin D might matter more at these earlier stages. This suggests timing of measurement and possibly timing of vitamin D status during pregnancy may be important factors.

Additional analyses looking at different ways vitamin D was measured, different vitamin D cutoff levels, different geographic regions, and different study designs all supported the general pattern that lower vitamin D appears linked to higher preeclampsia risk. This consistency across different approaches strengthens the suggestion of a real connection, even though individual measures weren’t statistically proven

Previous research had suggested a link between low vitamin D and preeclampsia risk, and this meta-analysis confirms that women with preeclampsia do tend to have lower vitamin D. However, this analysis is more cautious than some earlier claims, showing that the connection isn’t as straightforward as simply ’low vitamin D causes preeclampsia.’ The findings fit with a growing understanding that vitamin D plays multiple roles in pregnancy health

The biggest limitation is that all included studies were observational—researchers watched what happened naturally rather than randomly giving some women vitamin D and others a placebo. This means we can see that low vitamin D and preeclampsia occur together, but we can’t prove vitamin D deficiency causes preeclampsia. Other factors (like sun exposure, diet, genetics, or other health conditions) could explain both low vitamin D and preeclampsia risk. Different studies used different methods to measure vitamin D and different cutoff values for ‘deficiency,’ which made combining results more complicated. Finally, most studies were from developed countries, so results may not apply equally worldwide

The Bottom Line

Based on this research, maintaining adequate vitamin D levels during pregnancy appears sensible and may be beneficial, though it’s not yet proven to prevent preeclampsia specifically. Current recommendations suggest pregnant women should have vitamin D levels checked and may benefit from supplementation if levels are low. However, vitamin D supplementation should not be considered a proven prevention strategy for preeclampsia at this time. Talk with your healthcare provider about your individual vitamin D status and needs (Moderate confidence level)

Pregnant women and those planning pregnancy should be aware of this research, especially if they have risk factors for preeclampsia (like high blood pressure, obesity, or family history). Women living in areas with limited sun exposure or those with dietary restrictions may particularly benefit from discussing vitamin D with their doctor. This research is less relevant for non-pregnant individuals, though vitamin D remains important for overall health

If you start vitamin D supplementation during pregnancy, it typically takes several weeks to months to raise blood levels meaningfully. Benefits for pregnancy health would likely develop gradually throughout pregnancy rather than quickly. If you’re planning pregnancy, starting vitamin D optimization 2-3 months before conception may be ideal

Want to Apply This Research?

  • Track your vitamin D supplementation dose and timing daily (if taking supplements), and log any blood pressure readings if monitored at home. Note the date of any vitamin D blood tests and results to monitor trends over time
  • If your healthcare provider recommends vitamin D supplementation during pregnancy, set a daily reminder to take your supplement at the same time each day (such as with breakfast). Log this in your app to maintain consistency and share records with your healthcare provider
  • Work with your healthcare provider to get vitamin D levels checked at the beginning of pregnancy and again in the second trimester. Track these results in your app along with any blood pressure readings and preeclampsia screening results to identify patterns and share with your medical team

This research summary is for educational purposes only and should not replace professional medical advice. Preeclampsia is a serious pregnancy condition that requires medical supervision. If you are pregnant or planning pregnancy, discuss vitamin D screening and supplementation with your healthcare provider before making any changes. Do not use vitamin D supplementation as a substitute for regular prenatal care or medical monitoring. If you experience symptoms of preeclampsia (severe headache, vision changes, upper abdominal pain, or sudden swelling), seek immediate medical attention.