The characteristics of the light and heavy smokers included in this study are shown in Table 1. While there are roughly equal numbers of men and women among the heavy smokers, only 31% of the light smokers are men. These gender differences in smoking prevalence are consistent with those documented for Americans in the birth cohorts of the study population and are likely due to both cultural and biological factors (19). The heavy smokers were slightly less educated and likely to consume more alcohol than the light smokers. The percentages that were current smokers were low in both groups (1.5% for light smokers and 11.9% for heavy smokers), likely reflecting their advanced age (smoking prevalence of US adults aged ≥65 is less than 9%) (20). The characteristics of the individuals excluded from the analysis because of ethnic background or genotyping problems were similar to those included in the study (data not shown).
