Are exposure-disease relationships assessed in cohorts of health professionals generalizable?: a comparative analysis based on WCRF/AICR systematic literature reviews.

Abstract

Although cohorts of health professionals are not representative of the general US population, the generalizability of exposure-disease relationships identified in these cohorts has not been extensively evaluated. Our objective was to compare the associations of risk factors with cancer risk obtained in the Nurses' Health Study (NHS), Nurses' Health Study II (NHSII), and the Health Professionals Follow-Up Study (HPFS) with those from meta-analyses of cohort studies. Data were extracted from the most recent systematic literature reviews conducted by the World Cancer Fund/American Institute of Cancer Research (WCRF/AICR). We examined risk factors with "convincing," "probable," or "limited-suggestive" evidence for 17 cancer types. Cohort-specific results for NHS, NHSII, and HPFS and corresponding sex-specific pooled meta-analysis results were obtained when available. We compared associations for continuous variables and inspected potential non-linearity in the dose-response meta-analyses. Data for 88 comparisons across 11 cancer types were available. For most risk factors, we observed a close resemblance between the cohort-specific and corresponding sex-specific pooled associations. The 45 comparisons for factors considered as "convincing" or "probable" invariably exhibited similar associations in direction and magnitude. In 44 of the 45, the 95% CI from the NHS, NHSII, or HPFS captured the pooled estimate. In the one exception, the difference was 0.01. The NHS, NHSII, and HPFS studies are not representative of the general US population concerning sociodemographic and behavioral factors. However, the generalizability of the exposure-disease relationship assessed in these cohorts is not impaired by these factors.