Table 4.

Summary of pooled RRs for selenium and subgroup analyses

GroupsNo. of resultsNo. of cases*RR95% CIAdjusted 95% CIHeterogeneity P
RRs
    Overall1319730.740.62–0.880.57–0.97<0.01
    Overall with NPC study1420330.740.63–0.870.58–0.94<0.01
    Study design
        Cohort45010.810.60–1.100.51–1.300.07
        NCC910760.720.58–0.900.50–1.04<0.01
        Case-control25170.930.65–1.330.56–1.550.15
    Gender
        Men89120.680.54–0.860.46–1.02<0.01
        Women55720.740.53–1.04NA0.41
    Assessment
        Diet history/FFQ57011.000.77–1.30NA0.47
        Serum selenium610290.800.63–1.030.58–1.100.13
        Toenail selenium43640.460.32–0.660.24–0.870.03
    Smoking status
        Current smokers76200.560.42–0.770.33–0.98<0.01
        Noncurrent smokers52740.720.46–1.12NA0.74
        Former smokers22230.730.42–1.260.34–1.550.17
    Follow-up time§
        <10 years127620.700.55–0.900.43–1.15<0.01
        ≥10 years65960.790.60–1.030.57–1.090.21
    Population selenium level
        High47540.860.65–1.150.61–1.220.22
        Low68550.720.56–0.930.45–1.16<0.01
    Smoking adjustment
        Crude57180.790.60–1.050.52–1.210.06
        Smoking adjusted57180.820.61–1.120.53–1.280.08
Mean differences
    Serum selenium88761.02 ng/ml−0.47 to 2.510.05
        High3526−1.69 ng/ml−3.84 to 0.460.75
        Low53503.90 ng/ml1.84–5.960.99
 Toenail selenium
4
667
0.02 μg/g
0.01–0.04

0.31
  • Note: NA, not applicable.

  • * The actual numbers maybe higher because the Hartman et al. study did not provide case numbers.

  • Total number of studies and cases is greater than the number of studies and cases in the overall analysis because one cohort study assessing diet history of selenium and one NCC study assessing serum selenium were done in the same cohort (26, 27). Only the NCC study was included in the overall analysis, but diet history and serum results were included in the appropriate subgroup analyses. In the cohort study involving diet history, results were presented separately for smokers and nonsmokers.

  • Includes never smokers and former smokers.

  • § Total number of studies is greater than the number of studies in the overall analysis because some studies presented data for more than one follow-up period.

  • Mean selenium levels in the controls. Classified as “high” if serum selenium ≥ 100 ng/ml or daily dietary selenium intake ≥ 55 μg. Classified as “low” if serum selenium < 100 ng/ml or daily dietary selenium intake < 55 μg.

  • Mean difference defined as mean selenium level in controls minus mean selenium level in cases.