Selenium and Prostate Health: Evidence from the SELECT Trial
- What is selenium?
- Early promise – observational studies
- The SELECT trial – large randomised controlled trial
- SELECT results – no benefit, possible harm
- Current recommendations – do not take selenium supplements
- Food sources – Brazil nuts, fish, eggs
- Safe intake – RDA and upper limit
- Interactive FAQ – 9 questions about selenium and prostate health
What is selenium?
Selenium is an essential trace mineral that plays a role in antioxidant defence, thyroid hormone metabolism, and immune function. It is found in soil, and dietary intake varies by geographic region.
In the 1990s and early 2000s, selenium gained attention as a potential prostate cancer preventive agent due to its antioxidant properties and promising observational studies.
Early promise – observational studies
Before the SELECT trial, several studies suggested selenium might reduce prostate cancer risk:
- NPC trial (Nutritional Prevention of Cancer, 1996): Secondary analysis showed 50-60% lower prostate cancer risk in men taking selenium supplements (200 mcg/day).
- Observational studies: Higher selenium blood levels were associated with lower prostate cancer risk in some, but not all, studies.
These findings led to widespread use of selenium supplements and the large SELECT trial.
The SELECT trial – large randomised controlled trial
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was designed to definitively test whether selenium and/or vitamin E could prevent prostate cancer.
Trial design:
- Participants: 35,533 men aged 50+ (African descent) or 55+ (others)
- Interventions: Selenium (200 mcg/day), vitamin E (400 IU/day), both, or placebo
- Duration: Planned for 7-12 years, stopped early at 5.5 years
SELECT results – no benefit, possible harm
The SELECT trial was stopped early because interim analysis showed no benefit – and potential harm:
- No reduction in prostate cancer risk: Selenium alone had no effect on prostate cancer incidence.
- Increased risk with vitamin E alone: 17% higher risk of prostate cancer (statistically significant).
- Increased risk of high-grade cancer: Both selenium and vitamin E were associated with a small increase in high-grade prostate cancer (non-significant).
- Increased diabetes risk: Selenium supplementation was associated with a 10-15% increase in type 2 diabetes.
Long-term follow-up (additional 5-7 years):
- Vitamin E alone continued to show increased prostate cancer risk
- Selenium alone showed no benefit
- No benefit for either supplement
Current recommendations – do not take selenium supplements
Based on the SELECT trial and other evidence, major organisations recommend:
- American Cancer Society: Do not take selenium supplements for prostate cancer prevention.
- American Urological Association (AUA): Selenium is not recommended for prostate cancer prevention.
- USPSTF: Recommends against vitamin E or selenium for prostate cancer prevention.
Who might still need selenium?
- People living in regions with selenium-deficient soil (parts of China, Russia, Europe)
- People on long-term dialysis
- People with HIV/AIDS
Food sources – Brazil nuts, fish, eggs
Selenium is best obtained from food, not supplements. Good sources include:
- Brazil nuts: 1 nut = 70-100 mcg (exceeds daily needs – do not eat too many)
- Tuna (canned): 3 oz = 60-80 mcg
- Sardines: 3 oz = 40-50 mcg
- Eggs: 1 large egg = 15-20 mcg
- Sunflower seeds: 1/4 cup = 20-25 mcg
- Chicken (dark meat): 3 oz = 15-20 mcg
- Brown rice: 1 cup = 10-15 mcg
Selenium content varies by soil:
- North American soil is generally selenium-rich (Brazil nuts from Brazil are high regardless)
- European and Chinese soil may be selenium-poor
Safe intake – RDA and upper limit
While selenium is essential, too much can be toxic.
- Recommended Dietary Allowance (RDA): 55 mcg/day for adult men
- Tolerable Upper Intake Level (UL): 400 mcg/day
Symptoms of selenium toxicity (selenosis):
- Garlic breath odour
- Brittle hair and nails
- Nausea, diarrhoea
- Skin rash
- Nerve damage (in severe cases)
Interactive FAQ – Selenium and prostate health
No – the SELECT trial (35,000 men) showed no benefit. Selenium supplements do not reduce prostate cancer risk.
No benefit for selenium, increased prostate cancer risk with vitamin E, and increased diabetes risk with selenium.
No – major guidelines recommend against selenium supplements for prostate cancer prevention.
Brazil nuts, tuna, sardines, eggs, sunflower seeds, chicken, brown rice.
55 mcg/day (RDA for adult men). One Brazil nut provides 70-100 mcg – enough for the day.
Yes – upper limit is 400 mcg/day. Excess causes garlic breath, brittle hair/nails, nausea, nerve damage.
No evidence. Selenium is not recommended for BPH.
The NPC trial was not designed for prostate cancer – the finding was a secondary analysis. SELECT was designed to confirm and showed no benefit.
There is no evidence of benefit. Some studies suggest possible harm (increased high-grade cancer). Avoid supplements.
Disclaimer: This information is for educational purposes. Selenium supplements are not recommended for prostate cancer prevention. Consult a urologist at Vivekananda Hospital for personalised advice.