Researchers wanted to know if taking high-dose vitamin D supplements could help prevent prostate cancer from getting worse in men who were being monitored closely without immediate treatment. They gave 81 men vitamin D pills and 42 men placebo pills over two years. While the vitamin D didn’t prevent cancer progression as hoped, it did show some signs of reducing damage to cells’ genetic material. This suggests vitamin D might have some protective effects, but more research is needed to confirm whether it actually helps slow cancer growth.

The Quick Take

  • What they studied: Whether taking monthly high-dose vitamin D supplements could prevent prostate cancer from progressing in men who were being watched closely instead of receiving immediate treatment.
  • Who participated: 123 men aged 50-80 years old with newly diagnosed prostate cancer that had a medium risk of getting worse. They were all on ‘active surveillance,’ meaning doctors monitored them regularly without starting treatment right away.
  • Key finding: After two years, vitamin D supplementation did not prevent cancer progression or delay the need for treatment any better than placebo. However, men taking vitamin D showed improvements in some markers of cell damage, suggesting a possible protective effect that wasn’t strong enough to prevent cancer progression.
  • What it means for you: If you have early-stage prostate cancer being monitored, vitamin D supplements alone are not proven to prevent your cancer from progressing. However, the findings suggest vitamin D might have some protective benefits at the cellular level. Talk with your doctor about whether vitamin D is right for you as part of your overall health plan—don’t rely on it as a cancer prevention strategy.

The Research Details

This was a phase II randomized controlled trial, which means researchers randomly assigned men to receive either vitamin D or a fake pill (placebo) without knowing which group they were in. This type of study is considered strong evidence because it reduces bias. The men took either 50,000 international units (IU) of vitamin D or placebo once a month for two years. Researchers measured whether men needed to start cancer treatment (the main goal) and whether their cancer got worse (a secondary goal). They also tested blood samples to look at vitamin D levels and special markers that show if cells’ genetic material was damaged.

Using a randomized controlled trial design is important because it helps prove whether vitamin D actually causes any benefit, rather than just showing that people who take vitamin D happen to do better. By randomly assigning men to groups and using a placebo, researchers can be more confident that any differences are due to vitamin D and not other factors. Testing blood markers for cell damage gives researchers clues about how vitamin D might work in the body, even if it doesn’t prevent cancer progression.

This study has several strengths: it was double-blinded (neither doctors nor patients knew who got vitamin D), it was randomized (reducing bias), and it measured multiple outcomes. However, the study was relatively small (123 men total) and only lasted two years, which might not be long enough to see all effects. The vitamin D group had more participants (81) than the placebo group (42), which could affect comparisons. Published in a reputable journal (British Journal of Cancer) adds credibility to the findings.

What the Results Show

The main finding was that vitamin D supplementation did not prevent prostate cancer progression better than placebo. Men in the vitamin D group and placebo group had similar rates of needing to start cancer treatment during the two-year study. The vitamin D group successfully raised their blood vitamin D levels (from 72 to 92 nmol/L), while the placebo group’s levels stayed low (from 66 to 60 nmol/L), confirming the supplement was working as intended. Despite this increase in vitamin D, there was no meaningful difference in how many men needed treatment or how their cancer progressed between the two groups.

An interesting secondary finding was that men taking vitamin D showed improvements in some markers of cell damage (called CBMN markers) in their blood. These markers suggest that vitamin D might protect cells from genetic damage at a microscopic level. However, this cellular-level benefit didn’t translate into preventing cancer progression or delaying treatment. The two groups had similar rates of side effects, suggesting vitamin D was generally safe at this dose.

Previous research has suggested vitamin D might have protective effects against various cancers, but results have been mixed. This study adds to growing evidence that while vitamin D may have some cellular benefits, it’s not a reliable way to prevent prostate cancer from progressing. The findings align with other recent research showing that vitamin D alone is not sufficient to prevent cancer progression in men being monitored for early-stage disease.

The study had several limitations worth noting: it was relatively small with only 123 participants, which means results might not apply to larger populations. The two groups weren’t perfectly balanced (81 in vitamin D group versus 42 in placebo), which could affect comparisons. Two years might not be long enough to see all effects of vitamin D supplementation. The study only included men aged 50-80, so results may not apply to younger men. Finally, the study measured cell damage markers but didn’t fully explain why these improvements didn’t prevent cancer progression.

The Bottom Line

Based on this evidence, vitamin D supplementation at 50,000 IU monthly is not recommended as a treatment to prevent prostate cancer progression in men on active surveillance. However, maintaining adequate vitamin D levels through diet, sunlight, or supplements remains important for overall health. Men with early-stage prostate cancer should discuss vitamin D with their doctor as part of general wellness, but should not rely on it to prevent cancer progression. Confidence level: Moderate—this is one study, and more research is needed.

This research is most relevant to men aged 50-80 with newly diagnosed, early-stage prostate cancer being monitored without immediate treatment. Men with advanced prostate cancer, women, and younger men should not assume these findings apply to them. Anyone considering high-dose vitamin D supplementation should discuss it with their healthcare provider, especially if they have cancer or are at risk for it.

If you were to take vitamin D supplements, you would need to take them for at least two years to see any potential effects. However, based on this study, don’t expect vitamin D to prevent your cancer from progressing. Any benefits would likely be subtle and at the cellular level, not in preventing the need for treatment.

Want to Apply This Research?

  • If you have prostate cancer on active surveillance, track your vitamin D supplementation (yes/no each day) and your cancer monitoring appointments (PSA test results and imaging dates). Note any changes in symptoms or side effects. This helps you and your doctor see patterns over time.
  • If your doctor recommends vitamin D, set a monthly reminder to take your supplement on the same day each month. Also track your overall vitamin D intake from food sources like fatty fish, egg yolks, and fortified milk. Use the app to log these sources alongside your supplement.
  • Create a long-term tracking system that records: (1) vitamin D supplement adherence, (2) blood test results when available, (3) cancer monitoring appointments and results, and (4) any health changes. Review this data with your doctor every 6-12 months to assess whether vitamin D supplementation is helping your overall health, even if it’s not preventing cancer progression.

This research summary is for educational purposes only and should not replace professional medical advice. If you have prostate cancer or are at risk for it, consult with your oncologist or urologist before starting any supplements, including vitamin D. This study shows that high-dose vitamin D did not prevent cancer progression in this specific group of men—do not use vitamin D as a substitute for medical treatment or monitoring. Individual results may vary, and your doctor can help determine what’s appropriate for your specific situation.