Effect of secondhand smoking, determined by urinary cotinine level on bone health

Background: We evaluated the relationship between secondhand smoke (SHS) inhalation, as verified by urinary cotinine levels, and bone health. Methods: We analyzed the nationwide, population-based, cross-sectional health survey. We included 1936 men aged 50 years or older who checked bone mineral density (BMD) from the Korean National Health and Nutrition Examination Survey (2008-2010). Current smokers assessed by urinary cotinine levels higher than 500 ng/mL were excluded (n = 616). Exposure to SHS was determined using a 50 ng/mL urinary cotinine threshold. Results: The estimated prevalence of SHS exposure in our cohort was 13.9%. After adjusting for age and body mass index (BMI), T-scores at total femur (P < 0.001), femoral neck (P < 0.001), and lumbar spine (P = 0.004) were lower in SHS exposure versus nonexposure groups. Impaired bone health (osteopenia or osteoporosis) at femoral neck or lumbar spine was evident in 61.7% and 48.6% of SHS exposure and nonexposure cases, respectively (P = 0.004). Moreover, after adjusting for age, BMI, and health habits, the odds ratio for impaired bone health in the SHS exposure group was 1.89 (95% confidence interval: 1.31-2.74). Conclusions: Our findings suggest that SHS exposure, determined by urinary cotinine levels, is negatively associated with BMD and is a leading cause of impaired bone health in Korean men.