Tobacco smoke exposure and decreased serum and red blood cell folate levels: data from the Third National Health and Nutrition Examination Survey.

The aim of this cross-sectional study was to determine the effects of smoke exposure on serum and red blood cell folate levels. Data collected as part of the Third National Health and Nutrition Examination Survey were analyzed. Serum and red blood cell folate levels were measured in active smokers and nonsmokers with high, moderate, and low exposure to environmental tobacco smoke. After adjusting for dietary intake of folate and other covariates, we found that both smokers and nonsmokers with high smoke exposure had lower red blood cell folate levels than did nonsmokers with low smoke exposure (-86 nmol/l [95% confidence interval, CI, -101 to -71 nmol/l] for smokers; -50 nmol/l [95% CI -69 to -31 nmol/l] for nonsmokers with high smoke exposure, compared with nonsmokers with low smoke exposure). Similarly, after adjustment of dietary intake of folate and other covariates, the log serum folate level also was decreased (-0.29 log nmol/l [95% CI -0.33 to -0.25 log nmol/l] for smokers; -0.16 log nmol/l [95% CI -0.20 to -0.12 log nmol/l] for nonsmokers with high smoke exposure, compared with nonsmokers with low smoke exposure). Tobacco smoke exposure is associated with decreased folate levels, which may be a mechanism for some of the health effects of active and passive smoking.