Combs 1993

Methods	Cohort/sub‐cohort‐controlled cohort study Country: US
Participants	Participants: 1239 men and women Inclusion criteria: participants of the NPCT with valid selenium measurement at baseline Name of parent cohort: Nutritional Prevention of Cancer Trial (NPCT) Recruitment: see: Nutritional Prevention of Cancer Trial Outcome assessment: not stated Number of cases: Squamous cell cancer: 204 (male/female: n.r.) Case definition: incidence Years of follow‐up: 2.0 years Type of selenium marker: plasma
Interventions	d.n.a.
Outcomes	Statistical methods: Cox proportional hazard model Variables controlled in analysis: age, gender, current smoking, alcohol drinking
Risk estimates [95% CI]	Reference category (unadjusted RR): lower half Results: Squamous cell cancer both genders: higher half: unadjusted RR 0.69 (95% CI 0.51 to 0.92) both genders: "interquartile contrast" (high versus low), adjusted RR 0.79 (95% CI 0.67 to 0.94)
Selenium levels in exposure categories	lower half: ≤ 114.00 µg/l higher half: ≥ 114.10 µg/l
Notes