American Journal of Epidemiology Advance Access originally published online on May 8, 2009
American Journal of Epidemiology 2009 170(1):37-45; doi:10.1093/aje/kwp096
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ORIGINAL CONTRIBUTIONS |
Confounding by Dietary Patterns of the Inverse Association Between Alcohol Consumption and Type 2 Diabetes Risk
Correspondence to Dr. Paul F. Jacques, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging, 711 Washington Street, Boston, MA 02111 (e-mail: paul.jacques{at}tufts.edu).
Received for publication November 14, 2008. Accepted for publication March 25, 2009.
The ability to interpret epidemiologic observations is limited because of potential residual confounding by correlated dietary components. Dietary pattern analyses by factor analysis or partial least squares may overcome the limitation. To examine confounding by dietary pattern as well as standard risk factors and selected nutrients, the authors modeled the longitudinal association between alcohol consumption and 7-year risk of type 2 diabetes mellitus in 2,879 healthy adults enrolled in the Framingham Offspring Study (1991–2001) by Cox proportional hazard models. After adjustment for standard risk factors, consumers of 
9.0 drinks/week had a significantly lower risk of type 2 diabetes mellitus compared with abstainers (hazard ratio = 0.47, 95% confidence interval (CI): 0.27, 0.81). Adjustment for selected nutrients had little effect on the hazard ratio, whereas adjustment for dietary pattern variables by factor analysis significantly shifted the hazard ratio away from null (hazard ratio = 0.33, 95% CI: 0.17, 0.64) by 40.0% (95% CI: 16.8, 57.0; P = 0.002). Dietary pattern variables by partial least squares showed similar results. Therefore, the observed inverse association, consistent with past studies, was confounded by dietary patterns, and this confounding was not captured by individual nutrient adjustment. The data suggest that alcohol intake, not dietary patterns associated with alcohol intake, is responsible for the observed inverse association with type 2 diabetes mellitus risk.
alcohol drinking; bias (epidemiology); confounding factors (epidemiology); diabetes mellitus, type 2; diet; factor analysis, statistical; least-squares analysis; proportional hazards models
Abbreviations: CI, confidence interval; HRadj, hazard ratio adjusted for potential confounders; HRunadj, hazard ratio unadjusted for potential confounders
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