Researchers compared vitamin D levels in 132 women—66 with PCOS (a common hormone condition affecting fertility) and 66 without it. They found that women with PCOS were nearly twice as likely to have low vitamin D levels, even after accounting for weight and other factors. This suggests PCOS itself may affect how the body handles vitamin D, independent of body weight. The findings support the idea that women with PCOS should have their vitamin D checked and may benefit from vitamin D screening as part of their care.

The Quick Take

  • What they studied: Whether women with PCOS (a condition affecting hormones and fertility) have lower vitamin D levels compared to women without PCOS
  • Who participated: 132 women total: 66 with PCOS who were having trouble getting pregnant, and 66 healthy women without PCOS. Both groups were similar in age, education, and job status, but the PCOS group tended to weigh more and have lower income.
  • Key finding: Women with PCOS were about 1.9 times more likely to have vitamin D deficiency than women without PCOS, even after accounting for weight, age, income, and season. This means PCOS itself appears connected to low vitamin D, not just weight-related factors.
  • What it means for you: If you have PCOS, you may want to ask your doctor to check your vitamin D levels. While this study shows a connection, it doesn’t prove that vitamin D deficiency causes PCOS or that taking vitamin D will fix PCOS. More research is needed to understand if vitamin D supplements help with PCOS symptoms.

The Research Details

This was a case-control study, which means researchers looked back at medical information from two groups of women—those with PCOS and those without—and compared their vitamin D levels. The researchers used statistical methods to account for factors that could affect vitamin D levels, like how much each person weighed, their age, when blood samples were taken (season matters for vitamin D), and their income level. By adjusting for these factors, they tried to isolate whether PCOS itself was connected to vitamin D deficiency or if other factors were responsible.

The study included 66 women diagnosed with PCOS who were struggling to become pregnant, and 66 healthy women without PCOS as a comparison group. Both groups had their vitamin D levels measured through blood tests. The researchers then used mathematical analysis to calculate how much more likely women with PCOS were to have low vitamin D compared to the control group.

This research approach is important because it helps separate cause from effect. By comparing two similar groups and adjusting for known factors that affect vitamin D, researchers can better understand whether PCOS itself influences vitamin D levels or whether other things (like weight) are the real reason. This type of study is useful for identifying health patterns in specific populations and can guide future research.

This study has some strengths: it carefully matched the two groups and adjusted for multiple factors that could affect results. However, it’s a relatively small study (132 people total), which means the findings may not apply to all populations. The study was done in one location, so results may differ in other regions or countries. Because this is a case-control study, it shows an association (connection) between PCOS and vitamin D deficiency but cannot prove that one causes the other. Larger studies and clinical trials would be needed to confirm these findings and test whether vitamin D supplements actually help women with PCOS.

What the Results Show

The main finding was that women with PCOS had significantly lower vitamin D levels than women without PCOS. In the initial analysis, women with PCOS were 2.37 times more likely to have vitamin D deficiency. However, when researchers adjusted for weight (BMI), age, income level, and the season when blood was drawn, this number decreased to 1.89 times more likely. This adjustment is important because it shows that even after accounting for weight—which affects vitamin D levels—women with PCOS still had lower vitamin D.

The fact that the association remained significant after adjusting for these factors suggests that PCOS itself may play a role in vitamin D deficiency, beyond just the effects of being overweight. The researchers found that the two groups were similar in age, education, and employment, but differed in weight and income, which they accounted for in their analysis.

The study noted that socioeconomic status (income level) and body weight were different between the two groups, and both of these factors can affect vitamin D levels. The researchers controlled for these differences in their analysis. The timing of blood tests (season) was also considered, since vitamin D levels naturally vary based on sun exposure throughout the year. These secondary observations help explain why the adjusted results were different from the initial results.

Previous research has suggested a link between PCOS and vitamin D deficiency, but most studies have focused on whether vitamin D supplements help treat PCOS symptoms. This study adds to that body of research by providing local population data and showing that the connection between PCOS and low vitamin D remains even after accounting for weight. The findings support earlier research suggesting PCOS may independently affect vitamin D status, though more research is needed to understand the exact mechanism.

This study has several important limitations. First, it’s relatively small with only 132 participants, which means the results may not apply to all women or all populations. Second, it was conducted in one specific location, so results may differ in other regions with different climates, diets, or populations. Third, because this is a case-control study looking back at existing data, it can show that PCOS and vitamin D deficiency are connected, but it cannot prove that one causes the other. Fourth, the study only included women struggling with infertility, so results may not apply to all women with PCOS. Finally, the study didn’t measure vitamin D supplementation or sun exposure directly, which could affect results.

The Bottom Line

Based on this research, women with PCOS should consider asking their doctor to check their vitamin D levels (moderate confidence). If vitamin D deficiency is found, supplementation may be appropriate, though more research is needed to determine the best dose and whether it improves PCOS symptoms (low to moderate confidence). This study supports vitamin D screening as part of PCOS care, but it doesn’t prove that vitamin D supplements will treat PCOS or improve fertility.

Women with PCOS, especially those trying to become pregnant, should be aware of this connection and discuss vitamin D screening with their healthcare provider. Women without PCOS generally don’t need to change their approach based on this study. Healthcare providers caring for women with PCOS should consider vitamin D status as part of routine care. This research is less relevant to men or postmenopausal women.

If vitamin D deficiency is found and supplementation is started, it typically takes 8-12 weeks to see vitamin D levels improve in blood tests. However, it’s unclear from this study how long it would take to see improvements in PCOS symptoms like irregular periods or fertility issues. More research is needed to establish realistic timelines for symptom improvement.

Want to Apply This Research?

  • Track vitamin D levels quarterly (every 3 months) through blood tests ordered by your doctor. Record the date, vitamin D level (in ng/mL or nmol/L), and any supplements taken. Note the season to see if there’s a pattern.
  • If you have PCOS and low vitamin D, work with your doctor to start vitamin D supplementation. Use the app to set a daily reminder to take your vitamin D supplement at the same time each day. Log your supplement intake to maintain consistency.
  • Create a long-term tracking system that records: (1) vitamin D supplement dose and frequency, (2) quarterly blood test results, (3) PCOS-related symptoms (period regularity, energy levels, fertility status), and (4) sun exposure and season. This helps identify patterns and whether supplementation is making a difference over time.

This research shows an association between PCOS and vitamin D deficiency but does not prove that vitamin D deficiency causes PCOS or that vitamin D supplements will treat PCOS or improve fertility. This study is not a substitute for professional medical advice. Women with PCOS should consult with their healthcare provider before starting any new supplements or making changes to their treatment plan. Vitamin D supplementation should only be undertaken under medical supervision, as too much vitamin D can be harmful. Individual results may vary based on genetics, location, diet, and other factors not studied here.