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SOCIAL AND BIOLOGICAL FACTORS OVER THE LIFE COURSE

We present 2 examples of social and biological factors affecting health over the life course with applications to gender differences in health. These examples extend previous studies by Yang and Kozloski and illustrate the importance of addressing some of the underexplored issues we have outlined above.47,48 Based on data from about 38 000 adults in the National Health and Nutrition Examination Survey (NHANES) conducted between 1988–1994 (III) and 1999–2006, we estimated multivariate regression models to assess the parametric relationships of sex and age with various biological functions and assess how social behavioral factors may account for such relationships.
Figure 2 shows the age curves of the inflammation burden by sex and smoking status predicted from the best fitting model that adjusts for other covariates. The curves indicate that the female excess in inflammation decreases with age (P < .001 for the sex by age interaction). Interestingly, the patterns of age variations in sex differentials depend on smoking behaviors. Cigarette smoking is associated with elevated risks of inflammation for both sexes, but the association is significantly larger for men than women (P < .001 for the sex by smoking interaction), such that the sex gap before old age is much smaller, converges much earlier, and even reverses later in life for current smokers compared with never or past smokers.