Differential exposures to behavioral risk factors have been shown to play an important mediating role on the education–mortality relation. However, little is known about the extent to which educational attainment interacts with health behavior, possibly through differential vulnerability.
In a cohort study of 76,294 participants 30 to 70 years of age, we estimated educational differences in cause-specific mortality from 1980 through 2009 and the mediating role of behavioral risk factors (smoking, alcohol intake, physical activity, and body mass index). With the use of marginal structural models and three-way effect decomposition, we simultaneously regarded the behavioral risk factors as intermediates and clarified the role of their interaction with educational exposure.
Rate differences in mortality comparing participants with low to high education were 1,277 (95% confidence interval = 1,062 to 1,492) per 100,000 person-years for men and 746 (598 to 894) per 100,000 person-years for women. Smoking was the strongest mediator for cardiovascular disease, cancer, and respiratory disease mortality when conditioning on sex, age, and cohort. The proportion mediated through smoking was most pronounced in cancer mortality as a combination of the pure indirect effect, owing to differential exposure (men, 42% [25% to 75%]; women, 36% [17% to 74%]) and the mediated interactive effect, owing to differential vulnerability (men, 18% [2% to 35%], women, 26% [8% to 50%]). The mediating effects through body mass index, alcohol intake, or physical activity were partial and varied for the causes of deaths.
Differential exposure and vulnerability should be addressed simultaneously, as these mechanisms are not mutually exclusive and may operate at the same time.
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From the aDepartment of Public Health, Section of Social Medicine, University of Copenhagen, Copenhagen, Denmark; bDepartment of Public Health, Section of Biostatistics, University of Copenhagen, Copenhagen, Denmark; cResearch Center for Prevention and Health, Glostrup University Hospital, Glostrup, Denmark; dDepartment of Cardiology and the Copenhagen City Heart Study, Bispebjerg University Hospital, Copenhagen, Denmark; eDanish Cancer Society Research Center, Institute of Cancer Epidemiology, Copenhagen, Denmark; and fDanish Health and Medicines Authority, Medical Public Health Office, Copenhagen, Denmark.
Supported by the Commission of Social Inequality in Cancer (grant number SU08004).
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Correspondence: Helene Nordahl, Department of Public Health, Section of Social Medicine, University of Copenhagen, Øster Farimagsgade 5A, Post Box 2099, 1014 Copenhagen, Denmark. E-mail: firstname.lastname@example.org.