Peters 2008

Methods	Cohort study Country: US
Participants	Inclusion criteria: aged 50 to 76 years, participants recruited from subscribers of commercial mailing list, residents of western Washington state, non‐whites excluded, no malignant disease at baseline Name of parent cohort: Vitamins and lifestyle (VITAL) study Recruitment: 1 October 2000 to 31 December 2002 Type of selenium marker: supplemental intake (questionnaire: use of supplements over the last 10 years, mean supplemental intake / day calculated) Case definition: incidence Peters 2008: Participants: 35,242 men Outcome assessment: 31 December 2004 Number of cases: Prostate cancer: 818 (male/female: 818/0)  Years of follow‐up: 2 to 4 years Asgari 2009: Participants: 69,671 men and women Outcome assessment: 31 December 2006 Number of cases: Melanoma: 461 (male/female: n.r.) Years of follow‐up: 4 to 5 years
Interventions	d.n.a.
Outcomes	Peters 2008: Analysed cases: 818 of 830 cases analysed (reason for non‐inclusion: not reported) Statistical methods: Cox proportional hazard regression analysis Variables controlled in analysis: age, family history of prostate cancer, BPH, income, multivitamin use Asgari 2009: Analysed cases: one case not analysed (reason for non‐inclusion: not reported) Statistical methods: Cox proportional hazard regression Variables controlled in analysis: age, sex, education, family history of melanoma, personal history of non‐melanoma skin cancer, mole removal, freckles, sunburns, hair colour, reaction to sunlight exposure
Risk estimates [95% CI]	Reference category: no supplemental selenium intake (lowest exposure category) Peters 2008: Results: Prostate cancer highest exposure category: RR 0.90 (95% CI 0.62 to 1.30) Asgari 2009: Results: Melanoma highest exposure category HR 0.98 (95% CI 0.69 to 1.41)
Selenium levels in exposure categories	stratification according to supplemental selenium intake Peters 2008: lowest category: no supplemental intake highest category ≥ 51 µg/day Asgari 2009: lowest exposure category: no supplemental intake highest exposure category ≥ 50 µg/day
Notes