RATIONALE: Chemoprevention therapy is the use of certain drugs to try to prevent the development of cancer. Selenium may be effective in preventing cancer. It is not yet known which dose of selenium may be most effective in preventing cancer.

PURPOSE: Randomized pilot study to determine the effectiveness of selenium in preventing cancer in healthy people.

OBJECTIVES: I. Determine whether daily supplementation with selenium significantly reduces total cancer incidence and site-specific cancer incidence in the general population. II. Determine whether this regimen has a beneficial effect on mood.

OUTLINE: This is a randomized, double-blind, placebo-controlled, multicenter study. Participants are stratified according to age (60-64 vs 65-69 vs 70-74). Participants are randomized to one of four arms. Arm I: Participants receive oral placebo once daily. Arm II: Participants receive low-dose oral selenium once daily. Arm III: Participants receive moderate-dose oral selenium once daily. Arm IV: Participants receive high-dose oral selenium once daily. Treatment in all arms continues for up to 2 years in the absence of unacceptable side effects or diagnosis of cancer.

PROJECTED ACCRUAL: A total of 510 patients (170 per stratum) will be accrued for this study within 9-12 months.

DISEASE CHARACTERISTICS: Healthy men and women No prior diagnosis of cancer except non-melanoma skin cancer

PATIENT CHARACTERISTICS: Age: 60 to 74 Performance status: SWOG 0-1 Life expectancy: Not specified Hematopoietic: Not specified Hepatic: No active liver disease No known abnormal liver function Renal: No active kidney disease No known abnormal kidney function Other: HIV negative No diminished mental capacity that would preclude study

PRIOR CONCURRENT THERAPY: No other concurrent selenium supplements (50 ug/day or more)