Knekt 1990

Methods	Matched, nested case‐control study (Knekt 1990, Hakama 1990, Knekt 1988, Knekt 1996) Cohort study (Knekt 1991) Country: Finland
Participants	Inclusion criteria: no history of cancer at baseline Name of parent cohort: Social Insurance Institution's Mobile Clinic Health Examination Survey Recruitment: 1968 to 1972 Knekt 1990: Participants: 39,268: 21,172 men and 18,096 women Outcome assessment: 31 December 1980 Number of cases: Any cancer: 1096 (male/female: 597/499) Stomach cancer: 95 (male/female: 58/37) Colon and rectal cancer: 91 (male/female: 32/59) Lung cancer: 198 (male/female: 189/9) Prostate cancer: 51 (male/female: 51/0) Urinary tract cancer: 47 (male/female: 34/13) Pancreatic cancer: 45 (male/female: 22/23) Breast cancer: 90 (male/female: 0/90) Gynaecological cancer (without breast): 86 (male/female: 0/86) Basal cell carcinoma (skin): 126 (male/female: 64/62) Other: 267 (male/female: 147/120) Hakama 1990: Participants: number of participants n.r.; both genders Inclusion criteria: aged 15 years and older Outcome assessment: 1977 Number of cases: Any cancer: 766 (male/female: n.r.) Lung cancer: 151 (male/female: 151/0) Breast cancer: 67 (male/female: 0/67) Stomach cancer: 76 (male/female: n.r.) Prostate cancer: 37 (male/female: 37/0) Knekt 1988: Participants: 36,265: 21,172 men and 15,093 women Outcome assessment: 31 December 1977 Number of cases: Oesophageal and stomach cancer: 86 (male/female: 51/35) Colon and rectal cancer: 57 (male/female: 21/36) Knekt 1991: Participants: 4538 men Inclusion criteria: aged 20 to 69 years, with dietary history taken Outcome assessment: 1986 Number of cases: Lung cancer: 117 (male/female: 117/0) Knekt 1996: Participants: 1896 women Outcome assessment: 1980 Number of cases:      Ovarian cancer: 24 (male/female: 0/24) Case definition: incidence Years of follow‐up: 9 to 20 years Type of selenium marker: serum (Knekt 1990, Hakama 1990, Knekt 1988, Knekt 1996), intake (Knekt 1991: dietary history)
Interventions	d.n.a.
Outcomes	Knekt 1990: Statistical methods: conditional logistic regression Variables controlled in analysis: smoking Variables additionally controlled in analysis of highest four quintiles versus lowest quintile: occupation, BMI, parity, cholesterol, haematocrit Variables controlled by matching: age, gender, municipality, time of baseline examination, duration of storage of sample Hakama 1990: Analysed cases: 766 of 864 cases analysed (reason for non‐inclusion: no serum sample) Statistical methods: conditional logistic regression Variables controlled in analysis: smoking Variables additionally controlled in analysis of highest four quintiles versus lowest quintile: retinol level, alpha‐tocopherol level Variables controlled by matching: age, gender, municipality, time of baseline examination, duration of storage of sample Knekt 1988: Statistical methods: n.r. Variables controlled in analysis: smoking, serum cholesterol Variables controlled by matching: age, gender, municipality, time of baseline examination, duration of storage of sample Knekt 1991: Statistical methods: Cox‐proportional hazards model Variables controlled in analysis: age, smoking (data stratified according to smoking status) Knekt 1996: Statistical methods: conditional logistic regression Variables controlled by matching: age, gender, municipality, time of baseline examination, duration of storage of sample
Risk estimates [95% CI]	Knekt 1990: Reference category: lowest quintile Results: Any cancer male: highest quintile: OR 0.41 (CI not reported) above 20th percentile: OR 0.67 (CI not reported); cases during first 2 years of follow‐up excluded: 476 cases: OR 0.65 (95% CI 0.48 to 0.89) female: highest quintile: OR 0.86 (CI not reported) above 20th percentile: OR 0.93 (CI not reported); cases during first 2 years of follow‐up excluded: 423 cases: OR 0.97 (95% CI 0.68 to 1.39) Stomach cancer male: highest quintile: OR 0.09 (CI not reported) above 20th percentile: OR 0.26 (CI not reported); cases during first 2 years of follow‐up excluded: 43 cases: OR 0.24 (95% CI 0.09 to 0.69) female: highest quintile: OR 0.27 (CI not reported) above 20th percentile: OR 0.59 (CI not reported); cases during first 2 years of follow‐up excluded: 30 cases: OR 0.48 (95% CI 0.14 to 1.66) Colon and rectal cancer male: highest quintile: OR 0.53 (CI not reported) above 20th percentile: OR 0.69 (CI not reported); cases during first 2 years of follow‐up excluded: 29 cases: OR 1.01 (95% CI 0.18 to 5.65) female: highest quintile: OR 0.80 (CI not reported) above 20th percentile: OR 1.26 (CI not reported); cases during first 2 years of follow‐up excluded: 48 cases: OR 1.10 (95% CI 0.42 to 2.92) Lung cancer male: highest quintile: OR 0.30 (CI not reported) above 20th percentile: OR 0.60 (CI not reported); cases during first 2 years of follow‐up excluded: 153 cases: OR 0.66 (95% CI 0.37 to 1.19) female: third highest quintile: OR 4.62 (CI not reported) (quintile 4 and 5 did not contain any cases) Prostate cancer highest quintile: OR 1.15 (CI not reported) above 20th percentile: OR 1.13 (CI not reported); cases during first 2 years of follow‐up excluded: 46 cases: OR 1.00 (95% CI 0.42 to 2.40) Urinary tract cancer male: highest quintile: OR 0.81 (CI not reported) above 20th percentile: OR 0.89 (CI not reported); cases during first 2 years of follow‐up excluded: 26 cases: OR 0.34 (95% CI 0.06 to 2.06) female: highest quintile: OR 4.12 (CI not reported) above 20th percentile: not reported; cases during first 2 years of follow‐up excluded: 9 cases: OR 2.51 (95% CI 0.13 to 47.9) Pancreatic cancer male: fourth quintile versus lowest: OR 0.58 (CI not reported) (highest quintile did not contain any cases) above 20th percentile: OR 0.11 (CI not reported); cases during first 2 years of follow‐up excluded: not reported female: highest quintile: OR 3.49 (CI not reported) above 20th percentile: not reported; cases during first 2 years of follow‐up excluded: 22 cases: OR 0.86 (95% CI 0.21 to 3.52) Breast cancer highest quintile: OR 0.64 (CI not reported) above 20th percentile: OR 0.52 (CI not reported); cases during first 2 years of follow‐up excluded: 74 cases: OR 0.57 (95% CI 0.18 to 1.81) Gynaecological cancer (without breast) highest quintile: OR 0.96 (CI not reported) above 20th percentile: OR 0.91 (CI not reported); cases during first 2 years of follow‐up excluded: 70 cases: OR 1.03 (95% CI 0.43 to 2.50) Basal cell carcinoma (skin) male: highest quintile: OR 0.54 (CI not reported) above 20th percentile: OR 0.65 (CI not reported); cases during first 2 years of follow‐up excluded: 54 cases: OR 0.86 (95% CI 0.35 to 2.12) female: highest quintile: OR 1.55 (CI not reported) above 20th percentile: OR 1.73 (CI not reported); cases during first 2 years of follow‐up excluded: 52 cases: OR 1.54 (95% CI 0.64 to 3.73) Other or unspecified cancer: male: highest quintile: OR 0.42 (CI not reported) above 20th percentile: OR 0.72 (CI not reported); cases during first 2 years of follow‐up excluded: 110 cases: OR 0.70 (95% CI 0.36 to 1.36) female: highest quintile: OR 0.71 (CI not reported) above 20th percentile: OR 0.87 (CI not reported); cases during first 2 years of follow‐up excluded: 111 cases: OR 0.92 (95% CI 0.44 to 1.92) Hakama 1990: Reference category: highest quintile Results: Any cancer male: lowest quintile: OR 2.40 (CI not reported) lowest quintile vs. four highest quintiles: OR 1.60 (CI not reported) female: lowest quintile: OR 1.20 (CI not reported) lowest quintile vs. four highest quintiles:0.90 (CI not reported) Lung cancer  male: lowest quintile vs. four highest quintiles: OR 1.80 (CI not reported) Breast cancer lowest quintile vs. four highest quintiles: OR 3.10 (CI not reported) Stomach cancer male: lowest quintile vs. four highest quintiles: OR 6.70 (CI not reported) female: lowest quintile vs. four highest quintiles: OR 2.00 (CI not reported) Prostate cancer lowest quintile vs. four highest quintiles: OR 0.80 (CI not reported) Knekt 1988: Reference category: highest quintile Results: Oesophageal and stomach cancer male: lowest tertile: OR  2.20 (CI not reported) lowest quintile vs. four highest quintiles: OR 3.3 (95% CI 1.3 to 9.1) female: lowest tertile: OR 1.50 (CI not reported) lowest quintile vs. four highest quintiles: OR 2.4 (95% CI 0.7 to 8.3) Colon and rectal cancer   male: lowest tertile: OR 0.90 (CI not reported) lowest quintile vs. four highest quintiles: OR 1.7 (95% CI 0.4 to 7.7) female: lowest tertile: OR 0.60 (CI not reported) lowest quintile vs. four highest quintiles: OR 0.8 (95% CI 0.2 to 2.4) Knekt 1991: Reference category: highest tertile Results: Lung cancer male non‐smokers: lowest tertile: OR 1.03 (CI not reported) male smokers: lowest tertile: OR 0.83 (CI not reported) Knekt 1996: Reference category: highest tertile Results: Ovarian cancer lowest tertile: OR 1.15 (95% CI 0.19 to 4.06)
Selenium levels in exposure categories	Knekt 1990: lowest quintile: ≤ 48.90 µg/l; highest quintile  ≥ 78.00 µg/l Hakama 1990: quintiles: not specified Knekt 1988: both genders: lowest tertile: ≤ 56.90 µg/l; highest tertile ≥ 70.10 µg/l lowest quintile: ≤ 50 µg/l; highest four quintiles > 50 µg/l Knekt 1991: tertiles: n.r. Knekt 1996: lowest tertile: ≤ 56.90 µg/l; highest tertile: ≥ 68.10 µg/l
Notes	Primary publication: Knekt 1990 Other publications: Hakama 1990, Knekt 1988, Knekt 1991, Knekt 1996