Researchers studied 84 pregnant women in their third trimester to understand why some develop high blood pressure during pregnancy. They found that women with high blood pressure problems had lower vitamin D levels compared to healthy pregnant women. The study also showed that women with higher body weight were more likely to develop pregnancy-related high blood pressure. While calcium levels appeared normal in both groups, the findings suggest that vitamin D may play an important role in preventing dangerous blood pressure spikes during pregnancy. However, more research is needed before doctors can recommend specific vitamin D treatments to prevent these complications.

The Quick Take

  • What they studied: Whether vitamin D and calcium levels in pregnant women’s blood are connected to developing high blood pressure during pregnancy
  • Who participated: 84 pregnant women in their third trimester (last 3 months) from hospitals in Poland. 41 women had pregnancy-related high blood pressure problems, and 43 were healthy controls for comparison
  • Key finding: Pregnant women with high blood pressure had vitamin D levels of 27.8 ng/mL compared to 35.7 ng/mL in healthy women. For every 1 ng/mL increase in vitamin D, the risk of high blood pressure dropped by about 8%
  • What it means for you: If you’re pregnant or planning to become pregnant, maintaining adequate vitamin D levels may help reduce your risk of developing dangerous high blood pressure. However, this is preliminary evidence—talk to your doctor before making any changes to supplements

The Research Details

This was a cross-sectional study, which means researchers took a snapshot in time by measuring vitamin D and calcium levels in pregnant women and comparing those with high blood pressure to those without. The study included 84 women in their third trimester (the last three months of pregnancy) from two hospitals in Poland. Researchers measured different forms of vitamin D and calcium in the women’s blood using standardized laboratory tests. They then compared the measurements between the two groups and used statistical methods to account for other factors that might affect blood pressure, like body weight, age, and how far along the pregnancy was.

This research approach is important because it helps identify potential connections between nutrient levels and pregnancy complications. By comparing women who developed high blood pressure to those who didn’t, researchers can spot patterns. However, this type of study can only show associations, not prove that low vitamin D causes high blood pressure—it could be the other way around or something else entirely.

This study has some important limitations to consider: it’s relatively small (only 84 women), it only measured vitamin D at one point in time (the third trimester), and it was observational rather than experimental. The study was well-designed with standardized lab tests and proper statistical adjustments, but the small size and timing mean the results should be viewed as preliminary evidence rather than definitive proof

What the Results Show

Women with pregnancy-related high blood pressure had significantly lower vitamin D levels (27.8 ng/mL) compared to healthy pregnant women (35.7 ng/mL). This difference was statistically significant, meaning it’s unlikely to have happened by chance. When researchers adjusted for other factors like body weight and age, higher vitamin D levels remained protective—each 1 ng/mL increase in vitamin D was associated with an 8% lower risk of high blood pressure. Body weight also played an important role: for every 1 kg/m² increase in BMI (a measure of body weight relative to height), the risk of high blood pressure increased by 19%. The combination of these two factors could predict high blood pressure risk with fair accuracy (78% accuracy).

Interestingly, calcium levels—both total calcium and ionized calcium—were similar between the two groups, suggesting that calcium status alone may not be the main issue. The active form of vitamin D (1,25-dihydroxyvitamin D₃) was also similar between groups. Women in the control group reported using supplements more often (84%) compared to women with high blood pressure (73%), though the types and amounts of supplements varied and weren’t standardized.

These findings align with previous research suggesting vitamin D plays a role in blood pressure regulation during pregnancy. The connection between obesity and pregnancy-related high blood pressure is well-established in medical literature. However, this study adds to growing evidence that vitamin D insufficiency may be an independent risk factor, separate from weight issues. The preservation of normal calcium levels despite low vitamin D suggests the body maintains calcium balance through other mechanisms, which is consistent with how the body prioritizes calcium during pregnancy.

Several important limitations affect how much we can trust these results: (1) The study is small with only 84 women, making it harder to detect true patterns; (2) Vitamin D was measured only once in the third trimester, so we don’t know if levels were low earlier in pregnancy; (3) The study design is observational, so we can’t prove vitamin D deficiency causes high blood pressure—it could be the reverse or caused by something else entirely; (4) Supplement use wasn’t standardized or carefully tracked; (5) The study only included women from Poland, so results may not apply to other populations; (6) The study couldn’t determine whether vitamin D supplementation would actually prevent high blood pressure

The Bottom Line

Based on this preliminary evidence, pregnant women should discuss vitamin D status with their healthcare provider. Current general recommendations suggest pregnant women maintain vitamin D levels above 30 ng/mL, and this study supports that target. However, this single study is not strong enough to recommend specific vitamin D supplementation doses to prevent high blood pressure—larger, well-designed studies are needed first. Maintaining a healthy weight before and during pregnancy remains an important, evidence-based recommendation for reducing high blood pressure risk.

This research is most relevant to pregnant women, women planning pregnancy, and healthcare providers managing pregnancy complications. It’s particularly important for women with risk factors like obesity or a family history of high blood pressure. This study should NOT be used to self-diagnose or self-treat—always consult with your doctor before starting or changing supplements during pregnancy.

If vitamin D supplementation were to help prevent high blood pressure, benefits would likely develop gradually over weeks to months of consistent adequate levels. This is not a quick fix—vitamin D works through long-term effects on blood vessel function and inflammation. Any changes in blood pressure would typically be monitored over the course of pregnancy through regular prenatal checkups.

Want to Apply This Research?

  • Track weekly vitamin D intake (from food and supplements in IU or micrograms) alongside blood pressure readings at prenatal appointments. Note any symptoms like swelling, headaches, or vision changes that might indicate high blood pressure complications
  • Work with your healthcare provider to establish a consistent vitamin D supplementation routine if recommended. This might include taking a prenatal vitamin with vitamin D at the same time each day, or getting safe sun exposure when possible. Log supplement adherence in the app to maintain consistency
  • Monitor blood pressure trends across trimesters if you’re tracking pregnancy health. Note any correlation between vitamin D supplementation changes and blood pressure readings. Share this data with your healthcare provider at prenatal visits to inform personalized recommendations

This research is preliminary and observational in nature. It does not prove that vitamin D deficiency causes high blood pressure in pregnancy, and it should not be used to make medical decisions without consulting your healthcare provider. Pregnant women should not start, stop, or change any supplements without medical guidance. If you have high blood pressure during pregnancy or are at risk, work closely with your obstetrician or midwife for appropriate monitoring and treatment. This article is for educational purposes only and is not a substitute for professional medical advice.