American journal of epidemiology
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Independent effects of changes in biologic risk factors on type 2 diabetes incidence remain unclear. The authors examined whether associations between changes in biologic risk factors and diabetes risk are driven by initial or attained risk factor levels. Biologic risk factors were measured at baseline and at each 5-year interval follow-up (rounds 2, 3, and 4) among 4,204 initially healthy men and women, aged 20-59 years, participating in the Dutch Doetinchem Cohort Study (1987-2007). ⋯ Five-year increases in waist circumference and blood pressure and decreases in HDL cholesterol were positively associated with risk of diabetes after adjustment for initial levels but no longer after adjustment for attained levels: waist circumference (hazard ratio (HR) = 0.86, 95% confidence interval (CI): 0.69, 1.07), systolic blood pressure (HR = 0.96, 95% CI: 0.84, 1.10), diastolic blood pressure (HR = 0.96, 95% CI: 0.87, 1.06), and HDL cholesterol (HR = 0.91, 95% CI: 0.81, 1.01). In conclusion, the associations between changes in biologic risk factors and risk of diabetes are mainly driven by the attained levels. Hence, not the prior changes, but the attained levels seem to be of importance with regard to diabetes risk.
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Prospective epidemiologic studies generally rely on 1 baseline biologic sample from participants for measurement of prediagnostic biomarkers, assuming that 1 measurement adequately represents the participant's "typical" level. The body of work assessing the reproducibility of circulating serum 25-hydroxyvitamin D (25(OH)D) levels over time focuses almost exclusively on populations of European descent, and data for vitamin D-binding protein (VDBP) are virtually nonexistent. ⋯ VDBP levels were highly stable over time, with adjusted ICCs of 0.97 (95% CI: 0.96, 0.98) for blacks and 0.96 (95% CI: 0.93, 0.97) for whites. These findings suggest that single, baseline 25(OH)D and VDBP serum measurements provide reasonably representative measures of these compounds for both white and black adults, demonstrating their utility as epidemiologic biomarkers in prospective studies.
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The authors assessed the relation of hormonal and pregnancy-related factors to the incidence of sarcoidosis in the Black Women's Health Study. On biennial questionnaires, participants (US black women aged 21-69 years at baseline) reported data on diagnoses of sarcoidosis, reproductive history, and medication use. Cox regression models, adjusted for age, education, geographic region, smoking, and body mass index, were used to estimate incidence rate ratios and 95% confidence intervals. ⋯ In models that included both factors, the incidence rate ratios were 0.60 (95% confidence interval: 0.37, 0.97) for age at first birth ≥30 years versus <20 years (P-trend = 0.05) and 0.73 (95% confidence interval: 0.43, 1.24) for <5 years since last birth versus ≥15 years (P-trend = 0.15). No significant associations were observed with age at menarche, parity, lactation, oral contraceptive use, or female hormone use. These results suggest that later full-term pregnancy and longer exposure to endogenous female hormones may be related to a reduced risk of sarcoidosis.