Researchers studied 103 pregnant women to understand how vitamin D levels affect their blood health and their babies’ development. They found that pregnant women with low vitamin D had changes in their red blood cells and lower levels of folate and vitamin B12—nutrients important for healthy pregnancy. The study suggests that eating more fish and getting enough vitamin D during pregnancy may help protect both mother and baby. While this research is promising, doctors say more studies are needed to understand exactly how vitamin D affects pregnancy outcomes.

The Quick Take

  • What they studied: How vitamin D levels in pregnant women’s blood connect to changes in their red blood cells and other important nutrients like folate and vitamin B12
  • Who participated: 103 pregnant women who visited an obstetrics clinic during their pregnancy and were followed until they gave birth
  • Key finding: Pregnant women with low vitamin D had higher red blood cell counts but smaller red blood cells, plus lower levels of folate and vitamin B12 compared to women with normal vitamin D levels
  • What it means for you: If you’re pregnant or planning to become pregnant, maintaining adequate vitamin D levels—possibly through eating more fish and getting sunlight—may help keep your blood healthy and support your baby’s development. However, talk to your doctor before making major dietary changes.

The Research Details

This was an observational study where researchers collected information from 103 pregnant women during their regular doctor visits at an obstetrics clinic. The women were followed from their pregnancy through delivery, and researchers measured their vitamin D levels along with various blood markers like red blood cell counts, folate, and vitamin B12. The study also tracked how often women ate fish and looked at their babies’ measurements at birth. Because this was observational research, the scientists could identify connections between vitamin D and blood changes, but couldn’t prove that low vitamin D directly caused the blood changes.

This research approach is important because it follows real pregnant women over time, making the results more relevant to everyday life than laboratory studies. By measuring multiple blood markers together, researchers could see how vitamin D relates to several nutrients at once, giving a more complete picture of pregnancy health.

The study was approved by an institutional review board, which is a safety check for human research. The sample size of 103 women is moderate—large enough to find real patterns but small enough that results should be confirmed by larger studies. The researchers measured specific blood markers with standard laboratory tests, which are reliable. However, the study doesn’t prove cause-and-effect, only that these factors are connected.

What the Results Show

Pregnant women with low vitamin D had noticeably different blood patterns compared to women with normal vitamin D. Specifically, they had more red blood cells overall, but those cells were smaller than normal. This pattern suggests their bodies might be compensating for something. Additionally, women with low vitamin D had significantly lower levels of folate and vitamin B12—two nutrients that are especially important during pregnancy for preventing birth defects and supporting fetal development. The differences were statistically significant, meaning they weren’t likely due to chance.

The study found that eating fish more frequently was connected to higher vitamin D levels. This makes sense because fish, especially fatty fish like salmon, is one of the best natural food sources of vitamin D. This finding suggests that dietary choices can meaningfully affect vitamin D status during pregnancy.

Previous research has shown that vitamin D plays important roles in bone health, immune function, and gene regulation. This study adds new information by showing that vitamin D may also affect how the body produces and manages red blood cells and maintains adequate folate and B12 levels. The connection between vitamin D and these other nutrients hasn’t been extensively studied in pregnant women, making this research a valuable addition to what we know.

The study only included 103 women, which is a relatively small group. The research couldn’t prove that low vitamin D directly caused the blood changes—only that they were connected. The study didn’t randomly assign women to have low or normal vitamin D (which would be unethical), so other factors might explain the differences. The study also didn’t measure whether these blood changes actually affected baby health outcomes, which would be important to know.

The Bottom Line

Healthcare providers should encourage pregnant women and women planning pregnancy to maintain adequate vitamin D levels through a combination of safe sun exposure, vitamin D-rich foods (especially fish), and supplements if recommended by their doctor. The evidence suggests this is important, though more research is needed to fully understand the benefits. Confidence level: Moderate—the research is suggestive but not definitive.

This research is most relevant for pregnant women, women planning to become pregnant, and healthcare providers caring for these populations. It’s particularly important for women in northern climates or those with limited sun exposure, who are at higher risk for vitamin D deficiency. Women who don’t eat fish or have dietary restrictions should discuss vitamin D sources with their doctor.

Vitamin D levels can be improved within weeks to months through dietary changes or supplementation, but the effects on blood health and pregnancy outcomes develop gradually over the course of pregnancy. Most benefits would be seen when vitamin D levels are maintained throughout the pregnancy.

Want to Apply This Research?

  • Log weekly fish consumption and vitamin D supplement intake (if recommended by your doctor), then track vitamin D blood test results at prenatal appointments to see if dietary changes are working
  • Set a goal to eat fatty fish (salmon, mackerel, sardines) 1-2 times per week, and if your doctor recommends it, take a prenatal vitamin with vitamin D daily at the same time each day
  • Request vitamin D blood tests at your regular prenatal visits (typically every 4 weeks), log the results in the app, and note any changes in energy levels or symptoms that might relate to vitamin status

This research describes associations between vitamin D levels and blood markers in pregnant women but does not prove that vitamin D deficiency causes these changes or that correcting vitamin D will prevent pregnancy complications. Pregnant women should not make changes to their vitamin D intake, diet, or supplements without consulting their healthcare provider. This information is educational and should not replace professional medical advice. If you are pregnant or planning pregnancy, discuss your vitamin D status and appropriate supplementation with your obstetrician or midwife.