Weight changes after smoking cessation affect the risk of vertebral fractures: a nationwide population-based cohort study

BACKGROUND CONTEXT: Smoking cessation reduces the risk of vertebral and hip fractures but usually increases body weight. Since underweight is known as a risk factor for vertebral fractures, smoking cessation is considered to have a protective effect on vertebral fractures. However, the actual effect of weight change after smoking cessation on the risk of vertebral fractures remains uncertain. PURPPOSE: This study aimed to assess the risk of vertebral fractures among individuals who reported smoking cessation with a specific focus on changes in body weight. STUDY DESIGN: Retrospective cohort study based on nationwide health insurance database. PATIENT SAMPLE: Participants were from nationwide biennial health checkups between 2007 and 2009 conducted by the Korean National Health Insurance Service. Participants were followed up from 2010 to 2018 to find incidence of newly developed vertebral fractures. OUTCOME MEASURES: The incidence rate was defined as the incidence rate (IR) per 1,000 person-years (PY). Cox proportional regression analysis was used to analyze the risk of vertebral fracture to determine the hazard ratio (HR) associated with the incidence of vertebral fractures based on smoking status and weight changes. METHODS: Based on their self-reported questionnaires, the participants were classified into three groups: current smokers, quitters, and nonsmokers. The quitter was defined as an individual who were smokers in 2007 and ceased smoking in 2009. Individuals with smoking cessation were categorized according to the weight change between baseline and 2 years prior: weight maintenance (-5 >> 5 % of weight change), weight loss (<-5 % of weight change), and weight gain (>5 % of weight change). We used Cox proportional hazards analysis to determine the hazard ratio (HR) associated with the incidence of vertebral fractures based on smoking status and temporal weight change over 2 years. RESULTS: This study evaluated 913,805 eligible participants, of whom 672,858 were classified as nonsmokers, 34,143 as quitters, and 206,804 as current smokers. Among quitters, 2,372 (6.9%) individuals had weight loss, and 7,816 (22.9%) had weight gain over 2 years. About 23,952 (70.2%) individuals maintained their weight over 2 years. The overall risk of vertebral fractures was significantly higher in quitters (adjusted HR [aHR]=1.110, 95% confidence interval [CI] 1.0131 - 216) than in nonsmokers, but it was lower than in current smokers (aHR=1.197, 95%CI 1.143 - 1.253), regardless of weight change after smoking cessation. However, individuals who experienced weight loss after smoking cessation exhibited a notably higher risk of vertebral fractures than current smokers (aHR=1.321, 95%CI 1.004 - 1.461). In the female population, weight gain after smoking cessation was associated with a higher risk of vertebral fractures (aHR = 1.470, 95%CI 1.002 - 2.587) than in current female smokers. CONCLUSIONS: Maintaining weight after smoking cessation may mitigate the risk of vertebral fractures. Weight loss after smoking cessation adversely affects the protective effects of smoking cessation on vertebral fractures in the general population. (c) 2024 Elsevier Inc. All rights reserved.