Association of secondhand smoke with fracture risk in community-dwelling non-smoking adults in Korea

Although the detrimental effects of active smoking on bone health have been widely recognized, the impact of secondhand smoke exposure on fracture risk in non-smokers remains less understood. A total of 4843 non-smokers aged 40–69 years, who participated in the Korean Genome and Epidemiology Study from 2001 to 2018, were analyzed. The participants were categorized into two groups based on their exposure status to secondhand smoke: currently exposed and unexposed. The exposure group was subsequently divided into two subgroups based on the median weekly exposure time (high versus low groups). The incidence of new fractures was determined using self-reported questionnaires. The identified fractures were categorized according to the fracture site: overall, vertebral, hip, non-vertebral, and non-vertebral non-hip fractures. The mean age of the participants was 52.4 years (84.1% women). Exposure to secondhand smoke was associated with an increased risk of fracture (adjusted hazard ratio [aHR]: 1.27, P = 0.028) after adjusting for multiple covariates including age, sex, body mass index, household income, bone density of mid-shaft tibia, c-reactive protein, alcohol consumption, and history of fracture. Secondhand smoke remained as a significant risk factor for fracture, independent of the major osteoporotic fracture probabilities estimated using a fracture risk assessment tool (aHR: 1.24, P = 0.038). The high exposure group had higher risk of fracture than that of the unexposed group (aHR: 1.33, P = 0.025) whereas the fracture risk did not differ significantly between low exposure and unexposed groups (aHR: 1.18, P = 0.253), suggesting a potential dose–response relationship. Secondhand smoke showed robust association with increased risk of non-vertebral (aHR: 1.37, P = 0.008) or non-vertebral non-hip fractures (aHR: 1.36, P = 0.013), while its association with vertebral fracture was attenuated (aHR: 1.03, P = 0.908). Secondhand smoke was associated with an elevated risk of fracture in non-smokers, independent of clinical risk factors.