Participants were classified as never-smokers if they had not smoked at least 100 cigarettes in their lifetime. Former smokers were defined as individuals who had smoked 100 cigarettes in different their lifetime but were not currently smoking. For participants who reported current smoking, cigarette type was determined by the brand that they smoked at the time of the interview and were thereafter categorized as menthol or nonmenthol. Cumulative pack-years of smoking were calculated using the self-reported number of cigarettes smoked per day in the past 5 days for current smokers (or before quitting for former smokers) and the number of years of smoking. Serum cotinine was measured by an isotope-dilution high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometric method.

The limits of detection for serum cotinine were 0.05ng/ml for NHANES 1999�C2000 and the first phase of NHANES 2001�C2002 and 0.015ng/ml for the second phase of NHANES 2001�C2002 and NHANES 2003�C2004, resulting in 29.2% of observations below the limit of detection. Other Variables Information on sex, age, race/ethnicity, education, and use of medication for treating hypertension, diabetes mellitus, and hypercholesterolemia was collected by self-reported questionnaires. Race/ethnicity was subsequently categorized by NCHS as non-Hispanic White, non-Hispanic Black, Mexican American, other Hispanic, and others. Body mass index (BMI) was calculated by dividing measured weight in kilograms by measured height in meters squared. Blood pressure was measured following the American Heart Association guidelines.

Three (and in some cases, four) systolic and diastolic blood pressures were measured on the same day in the sitting position. Hypertension was defined as a mean systolic blood pressure ��140 mmHg, a mean diastolic blood pressure ��90 mmHg, a self-reported physician diagnosis, or use of antihypertensive medication. Diabetes mellitus was defined as a fasting serum glucose level of ��126mg/dl, a nonfasting serum glucose level of ��200mg/dl, a self-reported physician diagnosis, or medication use. Serum total cholesterol was measured enzymatically. High-density lipoprotein (HDL) cholesterol was measured by heparin-manganese precipitation for NHANES 1999�C2002 and by direct immunoassay for NHANES 2003�C2004. Serum creatinine was measured by a kinetic Jaff�� method and was calibrated to account for laboratory differences across survey Cilengitide years (Selvin et al., 2007). Estimated glomerular filtration rate was calculated from calibrated serum creatinine, age, sex, and race/ethnicity by using the Modification of Diet in Renal Disease Study formula (Levey et al., 2006; Selvin et al., 2007).