Selenium & Vitamin E: Do They Affect Prostate Cancer Risk?

observational-study PMID: 21990298

Quick Summary: A large study found that taking vitamin E supplements might slightly increase the risk of prostate cancer in healthy men. Selenium supplements, on the other hand, didn't seem to have a big impact, good or bad.

What The Research Found

Researchers looked at whether taking selenium or vitamin E supplements could prevent prostate cancer. They found:

Vitamin E: Men taking vitamin E had a slightly higher chance of developing prostate cancer.

Selenium: Selenium didn't seem to change the risk of prostate cancer much.

Both: Taking both supplements together didn't significantly affect the risk either.

Study Details

Who was studied: Over 34,000 healthy men in the US, Canada, and Puerto Rico.

How long: The study followed the men for about 7 to 12 years.

What they took:

Some men took selenium (200 micrograms daily).
Some men took vitamin E (400 IU daily).
Some men took both.
Some men took a placebo (a "dummy" pill).

What This Means For You

Talk to your doctor: If you're considering taking vitamin E supplements, especially in high doses, discuss the potential risks with your doctor.

Focus on a balanced diet: Getting nutrients from food is generally safer than relying on supplements. Eat plenty of fruits, vegetables, and whole grains.

Don't use vitamin E for prevention: This study suggests vitamin E may not help prevent prostate cancer, and could even be harmful.

Study Limitations

It's not the whole story: This study only looked at men, and the results might not apply to women.

Specific forms matter: The study used a specific type of vitamin E. Other types might have different effects.

Other factors: The study didn't account for everything, like what people ate or their family history.

Stopped early: The study was stopped before it was supposed to end, which might have affected the results.

Key Findings

The SELECT trial found no significant reduction in prostate cancer risk with selenium (200 μg/day), vitamin E (400 IU/day), or their combination. However, vitamin E supplementation alone was associated with a statistically significant 17% increased risk of prostate cancer (HR: 1.17; 99% CI: 1.004–1.36; P = .008), translating to 1.6 additional cases per 1,000 person-years. Selenium showed a nonsignificant 9% increase (HR: 1.09; 99% CI: 0.93–1.27; P = .18), while the combination group had a 5% increase (HR: 1.05; 99% CI: 0.89–1.22; P = .46).

Study Design

This multicenter, randomized, double-blind, placebo-controlled clinical trial enrolled 35,533 men across 427 U.S., Canadian, and Puerto Rican sites from 2001–2004. Participants were aged ≥50 years (Black men) or ≥55 years (others), with normal prostate-specific antigen (PSA) levels (≤4.0 ng/mL) and digital rectal exams. Follow-up continued until 2011, with a primary analysis of 34,887 men.

Dosage & Administration

Selenium (200 μg/day as L-selenomethionine) and vitamin E (400 IU/day as all-rac-α-tocopheryl acetate) were administered orally. Groups received either selenium alone, vitamin E alone, both, or placebos. Supplementation continued for 7–12 years, with median follow-up of ~5.5 years.

Results & Efficacy

Vitamin E alone: 620 prostate cancer cases vs. 529 in placebo (HR: 1.17; 99% CI: 1.004–1.36; P = .008).
Selenium alone: 575 cases (HR: 1.09; 99% CI: 0.93–1.27; P = .18).
Combination: 555 cases (HR: 1.05; 99% CI: 0.89–1.22; P = .46).
Absolute risk increases per 1,000 person-years: 1.6 (vitamin E), 0.8 (selenium), 0.4 (combination).

Limitations

Early trial termination: SELECT was halted in 2008 due to futility, potentially limiting long-term conclusions.
Population specificity: Participants were predominantly older men with normal PSA; findings may not apply to younger men or those with elevated baseline risk.
Supplement form: Synthetic vitamin E (all-rac-α-tocopheryl acetate) differs from natural forms, and L-selenomethionine may not represent other selenium compounds.
Baseline nutrient status: Selenium levels were not measured pre-randomization, which could influence outcomes.
Confounding variables: Diet, lifestyle, and genetic factors were not controlled for in the analysis.

Clinical Relevance

The SELECT trial raises concerns about vitamin E supplementation, suggesting it may increase prostate cancer risk in older men. Selenium showed no significant benefit or harm, but its lack of efficacy contradicts earlier observational studies. These results advise against using vitamin E for prostate cancer prevention and highlight the need to evaluate supplement forms and dosages carefully. Clinicians should caution patients against high-dose vitamin E and emphasize that "normal" baseline health metrics (e.g., PSA) do not eliminate potential risks of long-term supplementation.

Word count: ~380