Researchers studied how vitamin D levels affect blood pressure and inflammation during pregnancy, and discovered that the baby’s sex matters. They found that pregnant women with obesity or high blood pressure had lower levels of active vitamin D, especially when carrying male babies. The study suggests that maintaining healthy vitamin D levels during pregnancy may be particularly important for women carrying boys. This research helps explain why some pregnancies develop complications and points to vitamin D as a potentially protective nutrient.

The Quick Take

  • What they studied: How vitamin D levels in pregnant women relate to blood pressure and inflammation in the placenta, and whether the baby’s sex makes a difference
  • Who participated: 142 pregnant women and their babies, divided into three groups: women with normal pregnancies, women with obesity, and women who developed preeclampsia (dangerously high blood pressure during pregnancy)
  • Key finding: Pregnant women carrying male babies who had obesity or preeclampsia showed significantly lower levels of active vitamin D in their cord blood. In healthy pregnancies, higher vitamin D levels were linked to lower blood pressure, but this protective effect disappeared in women with obesity or preeclampsia.
  • What it means for you: If you’re pregnant or planning to become pregnant, maintaining adequate vitamin D levels may help protect against high blood pressure and inflammation—especially if you’re carrying a boy. However, this is early-stage research, and you should discuss vitamin D supplementation with your doctor rather than self-treating.

The Research Details

Scientists collected blood samples from 142 pregnant women during each trimester of pregnancy and again from the umbilical cord blood after delivery. They measured two forms of vitamin D: calcidiol (the storage form) in the mother’s blood throughout pregnancy, and calcitriol (the active form) in the baby’s cord blood at birth. They also examined placental tissue to measure inflammation-related genes. The researchers compared three groups: women with normal pregnancies, women with obesity, and women who developed preeclampsia (a serious pregnancy complication involving high blood pressure).

The study was designed to look for sex-specific differences, meaning the researchers specifically analyzed whether findings differed between pregnancies carrying male versus female babies. This approach was based on previous research suggesting that the placenta processes vitamin D differently depending on the baby’s sex.

All measurements and gene analyses were performed using standard laboratory techniques, and the researchers used statistical methods to identify correlations between vitamin D levels, blood pressure, and inflammatory markers.

Understanding how vitamin D works differently in male versus female pregnancies is important because it may explain why some women develop complications like preeclampsia while others don’t. If vitamin D metabolism is truly different based on fetal sex, this could lead to personalized recommendations for pregnant women. Additionally, identifying modifiable factors like vitamin D status that relate to pregnancy complications could help prevent serious health problems for both mother and baby.

This study examined real pregnancy outcomes in a defined group of women, which is stronger than laboratory-only research. The researchers measured vitamin D at multiple time points throughout pregnancy rather than just once, providing a more complete picture. However, the study is observational, meaning it shows associations rather than proving cause-and-effect relationships. The sample size of 142 is moderate—larger studies would provide more confidence in the findings. The research was published in a peer-reviewed journal focused on pregnancy complications, suggesting it met scientific standards for publication.

What the Results Show

The most striking finding was that pregnant women carrying male babies who had either obesity or preeclampsia showed significantly lower levels of active vitamin D (calcitriol) in the umbilical cord blood compared to women with normal pregnancies. This reduction in active vitamin D was not as pronounced in pregnancies carrying female babies.

In women with normal pregnancies, higher maternal vitamin D levels throughout pregnancy were associated with lower blood pressure. However, this protective relationship disappeared in women with obesity or preeclampsia, suggesting that these conditions interfere with vitamin D’s blood pressure-lowering effects.

The placentas from women with preeclampsia, particularly those carrying male babies, showed increased activity of genes related to inflammation and blood pressure regulation. When vitamin D metabolites were higher, these inflammatory genes were less active, suggesting vitamin D may help calm inflammation in the placenta.

Women with obesity or preeclampsia had higher pre-pregnancy body mass index (BMI), lower cord blood vitamin D, and more active inflammatory genes in the placenta—a pattern that was especially pronounced in male-bearing pregnancies.

The study found that vitamin D metabolites showed inverse correlations with genes involved in both inflammation and high blood pressure regulation. This means that as vitamin D levels increased, the activity of these problematic genes decreased. Additionally, vitamin D levels were inversely related to pre-pregnancy body mass index, suggesting that women who were heavier before pregnancy tended to have lower vitamin D levels. The researchers noted that the placental processing of vitamin D appears to be fundamentally different in pregnancies carrying male versus female babies, with male pregnancies showing more pronounced vitamin D-related changes.

Previous research has established that vitamin D helps reduce inflammation and lower blood pressure in non-pregnant populations. This study extends that knowledge by showing that vitamin D’s protective effects may work differently during pregnancy and may depend on the baby’s sex. The finding that obesity and preeclampsia both involve altered vitamin D metabolism aligns with earlier studies suggesting these conditions share common inflammatory pathways. However, the specific discovery that male fetuses appear more vulnerable to vitamin D deficiency in the context of maternal obesity or preeclampsia is relatively novel and adds an important sex-specific dimension to pregnancy nutrition research.

This study shows associations between vitamin D levels and pregnancy outcomes but cannot prove that low vitamin D causes preeclampsia or obesity-related complications. The researchers did not randomly assign women to different vitamin D levels (which would be unethical), so they can only observe natural variations. The sample size of 142 women is moderate; larger studies would provide more definitive answers. The study measured vitamin D at specific time points but didn’t track all women identically, which could introduce variation. Additionally, the researchers couldn’t account for all factors that might affect vitamin D levels, such as sun exposure, dietary intake, or supplements women may have taken. Finally, the findings are specific to the populations studied and may not apply equally to all ethnic or geographic groups.

The Bottom Line

Based on this research, pregnant women should discuss vitamin D status with their healthcare provider and may benefit from ensuring adequate vitamin D intake through diet, supplements, or safe sun exposure—particularly if carrying a male baby or if they have obesity. Current prenatal care guidelines already recommend vitamin D supplementation for many pregnant women, and this research provides additional support for that practice. However, the strength of evidence is moderate; this is one study that should be confirmed by larger research before making major changes to clinical practice. Women should not self-supplement without medical guidance, as excessive vitamin D can also be harmful.

This research is most relevant to pregnant women, women planning pregnancy, and healthcare providers caring for pregnant patients. It’s particularly important for women with obesity, those at risk for preeclampsia, or those carrying male babies. Women with normal pre-pregnancy weight and no risk factors for preeclampsia should still maintain adequate vitamin D but may have lower risk. This research is less directly applicable to non-pregnant individuals, though it adds to the general evidence supporting vitamin D’s health benefits.

Vitamin D’s effects on blood pressure and inflammation develop gradually throughout pregnancy. The study measured vitamin D across all three trimesters, suggesting that maintaining adequate levels throughout pregnancy—not just at the end—is important. Women who optimize their vitamin D status before becoming pregnant may see benefits from the earliest stages of pregnancy. If vitamin D supplementation is started during pregnancy, benefits would likely accumulate over weeks to months rather than appearing immediately.

Want to Apply This Research?

  • Track weekly vitamin D intake (through food, supplements, and estimated sun exposure in minutes) alongside blood pressure readings if available. For pregnant users, correlate these with any prenatal visit notes about blood pressure or vitamin D levels. Set a goal of consistent daily vitamin D intake as recommended by your healthcare provider.
  • Users should establish a daily vitamin D routine: take supplements at the same time each day (if prescribed), eat vitamin D-rich foods (fatty fish, egg yolks, fortified milk), and get safe sun exposure when possible. For pregnant users specifically, log these behaviors and any prenatal blood pressure measurements to see personal patterns over time.
  • Create a long-term tracking dashboard showing monthly vitamin D intake consistency, blood pressure trends (if applicable), and pregnancy trimester. Set reminders for prenatal appointments where vitamin D levels might be checked. For women planning pregnancy, establish baseline vitamin D status 2-3 months before conception if possible. Track seasonal variations in vitamin D intake and sun exposure, as these naturally fluctuate.

This research describes associations between vitamin D levels and pregnancy outcomes but does not prove cause-and-effect relationships. The findings are from a single observational study and should not be used as the sole basis for medical decisions. Pregnant women or those planning pregnancy should consult with their healthcare provider before starting, stopping, or changing vitamin D supplementation. This information is educational and not a substitute for professional medical advice. Women with preeclampsia or pregnancy complications require medical supervision and should not rely on vitamin D supplementation alone for treatment. Individual vitamin D needs vary based on many factors including geography, skin tone, diet, and health status.