Researchers followed over 51,000 women for nearly 14 years to understand how vitamin D affects cancer risk before menopause. They found that women with low vitamin D levels had a higher chance of developing ovarian and uterine cancer. The study suggests that maintaining healthy vitamin D levels through sunlight, food, or supplements might help protect against these cancers. However, more research is needed to confirm these findings and understand exactly how vitamin D works to prevent cancer.

The Quick Take

  • What they studied: Whether vitamin D levels in the blood affect the chances of getting ovarian cancer, breast cancer, or uterine cancer in women before menopause
  • Who participated: Over 51,000 women from the UK Biobank (a large health database) who were tracked for an average of 13.8 years. The study focused on premenopausal women and included various ages, lifestyles, and health backgrounds
  • Key finding: Women with low vitamin D levels (below 50 nmol/L) were about 46% more likely to develop ovarian cancer and 37% more likely to develop uterine cancer compared to women with higher vitamin D. For every small increase in vitamin D, ovarian cancer risk dropped slightly
  • What it means for you: Getting enough vitamin D through sun exposure, food, or supplements may help reduce your risk of certain women’s cancers before menopause. However, this study shows a connection, not proof that vitamin D prevents cancer. Talk to your doctor about your vitamin D levels and whether supplementation is right for you

The Research Details

This was a prospective cohort study, which means researchers followed real people over time and tracked what happened to them. They used data from the UK Biobank, a massive health database with information from over 500,000 people. The researchers looked at vitamin D blood levels at the start and then watched to see who developed cancer over the next 13.8 years on average.

The scientists used a statistical method called Cox regression to analyze the data. This method helps them figure out if low vitamin D was connected to higher cancer rates, while accounting for other factors that might affect cancer risk (like smoking, weight, alcohol use, and sleep). They also looked at subgroups to see if certain lifestyle factors made the vitamin D connection stronger or weaker.

The study measured vitamin D as 25-hydroxyvitamin D, which is the form doctors check in blood tests. They compared women with very low levels (below 50 nmol/L) to those with higher levels, and also looked at what happened with each small increase in vitamin D.

This research approach is valuable because it follows real people in their everyday lives rather than testing them in a lab. This makes the findings more relevant to how vitamin D actually affects cancer risk in the real world. The large number of participants (over 51,000) makes the results more reliable than smaller studies. By looking at subgroups, the researchers could see if vitamin D’s protective effect worked differently depending on other lifestyle choices like drinking alcohol or getting enough sleep.

This study has several strengths: it’s large, it followed people for a long time, and it measured vitamin D directly from blood tests rather than relying on what people remembered. However, the study shows a connection between low vitamin D and cancer, not proof that vitamin D prevents cancer. Other unmeasured factors could explain the connection. The study is from a UK population, so results might differ in other countries or ethnic groups. Additionally, the study only looked at premenopausal women, so findings may not apply to older women

What the Results Show

During the study period, about 5.1% of all women developed some type of cancer. More specifically, 4.4% developed breast cancer, 0.5% developed uterine cancer, and 0.3% developed ovarian cancer. Women with low vitamin D levels (below 50 nmol/L) had notably higher risks: they were 46% more likely to develop ovarian cancer and 37% more likely to develop uterine cancer compared to women with adequate vitamin D.

The researchers also found that for every 10-unit increase in vitamin D levels, the risk of ovarian cancer dropped by about 10%. This suggests a dose-response relationship—meaning more vitamin D appears to offer more protection. Interestingly, breast cancer risk did not show a clear connection to vitamin D levels in this study.

The study also revealed that certain lifestyle factors made the vitamin D connection even stronger. Women with low vitamin D who also drank alcohol or slept less than 6 hours per night had even higher risks of ovarian and uterine cancer. This suggests that vitamin D’s protective effect might work better when combined with other healthy habits.

The research found that vitamin D supplementation appeared to modify the relationship between low vitamin D and cancer risk, suggesting that taking supplements might help. The protective effect of vitamin D seemed stronger in women who had adequate sleep (6 hours or more) and those who didn’t drink alcohol. Women with normal weight (healthy BMI) showed clearer vitamin D-cancer connections than those who were overweight. The study also found that outdoor exposure and other lifestyle factors influenced how important vitamin D levels were for cancer prevention

Previous research has shown mixed results about vitamin D and female cancers. Some studies found protective effects, while others found no connection. This large, long-term study adds important evidence that vitamin D may indeed protect against ovarian and uterine cancers specifically. However, the lack of a clear connection with breast cancer differs from some earlier research, suggesting the relationship between vitamin D and breast cancer may be more complex than initially thought. This study helps clarify that vitamin D’s protective effects may vary depending on the type of cancer

This study shows a connection between vitamin D and cancer risk, but cannot prove that low vitamin D causes cancer. Other factors not measured in the study could explain the connection. The study only included people from the UK, so results might be different in other countries or populations. The study focused on premenopausal women, so findings may not apply to postmenopausal women or men. Some women may have changed their vitamin D levels during the study (through supplements or sun exposure), but this wasn’t tracked. The study relied on a single vitamin D measurement at the beginning, which might not represent a person’s typical vitamin D level over many years

The Bottom Line

Based on this research, maintaining adequate vitamin D levels appears beneficial for reducing ovarian and uterine cancer risk in premenopausal women (moderate confidence level). Current health guidelines recommend 600-800 IU of vitamin D daily for most adults, though some experts suggest higher amounts. Consider getting your vitamin D level checked by your doctor, especially if you have limited sun exposure, live in northern climates, or have dark skin (which reduces vitamin D production from sunlight). If your levels are low, discuss supplementation options with your healthcare provider. Additionally, combine vitamin D efforts with other cancer-prevention strategies: limit alcohol, get adequate sleep (7-9 hours), maintain a healthy weight, and don’t smoke

This research is most relevant to premenopausal women concerned about ovarian and uterine cancer risk. Women with family histories of these cancers, those living in areas with limited sunlight, or those with dietary restrictions that limit vitamin D intake should pay particular attention. The findings may also interest healthcare providers counseling women about cancer prevention. However, women with breast cancer history should discuss vitamin D with their doctors, as the connection is less clear. The study doesn’t apply to postmenopausal women or men, though vitamin D remains important for overall health in these groups

If you start optimizing your vitamin D levels, you won’t see immediate cancer prevention benefits—cancer develops over many years. However, maintaining adequate vitamin D supports overall bone health, immune function, and mood within weeks to months. The protective effect against cancer likely develops over years of consistent adequate vitamin D levels, similar to how the study participants were followed for an average of 13.8 years. Think of vitamin D as part of long-term cancer prevention strategy rather than a quick fix

Want to Apply This Research?

  • Track your vitamin D supplementation daily (if taking supplements) and note your sun exposure time weekly. Set a goal of 15-30 minutes of midday sun exposure 3-4 times per week, or consistent supplement use as recommended by your doctor. Log any blood test results showing vitamin D levels to monitor trends over time
  • If your vitamin D is low, commit to one specific action: either take a daily vitamin D supplement at a consistent time (like with breakfast), or schedule regular outdoor time during midday hours. Pair this with tracking alcohol intake and sleep duration, as the study showed these factors interact with vitamin D’s protective effects. Set reminders for supplement timing or outdoor activity to build the habit
  • Check vitamin D levels annually through blood tests with your doctor, especially if you’re making changes to supplementation or sun exposure. Track sleep duration and alcohol consumption weekly in the app to identify patterns. Monitor any changes in these lifestyle factors and correlate them with your vitamin D levels over 6-12 months to see if your efforts are working. Share results with your healthcare provider to adjust your vitamin D strategy if needed

This research shows a connection between vitamin D levels and cancer risk, but does not prove that vitamin D prevents cancer. This information is for educational purposes and should not replace professional medical advice. If you have concerns about cancer risk, family history of cancer, or questions about vitamin D supplementation, please consult with your healthcare provider or oncologist. Do not start, stop, or change any supplements or medications without discussing with your doctor first. This study applies specifically to premenopausal women and may not be relevant to other populations. Always seek personalized medical guidance for your individual health situation.