Joint association of smoking and physical activity with mortality in elderly hypertensive patients: A Chinese population-based cohort study in 2007–2018

Background: Although associations of physical activity and smoking with mortality have been well-established, the joint impact of physical activity and smoking on premature mortality among elderly hypertensive population was still unclear. This study aimed to assess association of physical activity, smoking, and their interaction with all-cause and cardiovascular disease (CVD) mortality risk in elderly hypertensive patients. Methods: We included 125,978 Chinese hypertensive patients aged 60-85 years mean (SD) age, 70.5 (6.9) years who had records in electronic health information system of Minhang District of Shanghai, China in 2007-2015. Cox regression was used to estimate individual and joint association of smoking and physical activity on all-cause and CVD mortality. Interactions were measured both additively and multiplicatively. Additive interaction was evaluated by relative excess risk due to interaction (RERI), attributable proportion due to interaction (AP) and synergy index (S). Results: Among 125,978 elderly hypertensive patients (median age 70.1), 28,250 deaths from all causes and 13,164 deaths from CVD were observed during the follow-up up to 11 years. There was an additive interaction between smoking and physical inactivity RERI: all-cause 0.19 (95% CI: 0.04-0.34), CVD 0.28 (0.06-0.50); AP: all-cause 0.09 (0.02-0.16), CVD 0.14 (0.04-0.23); S: all-cause 1.21 (1.04-1.42), CVD 1.36 (1.06-1.75), while the concurrence of both risk factors was associated with more than 2-fold risk of death hazard ratio (HR): all-cause 2.10 (1.99-2.21), CVD 2.19 (2.02-2.38). Conclusion: Our study suggested that smoking and physical inactivity together may have amplified association on premature death compared to the sum of their individual associations, highlighting the importance of improving behavioral factors in combination and promoting a comprehensive healthy lifestyle in hypertensive elderly.