Physical activity attenuates the associations of systemic immune-inflammation index with total and cause-specific mortality among middle-aged and older populations

Systemic immune-inflammation index (SII) emerged as a biomarker of chronic inflammation and an independent prognostic factor for many cancers. We aimed to investigate the associations of SII level with total and cause-specific mortality risks in the general populations, and the potential modification effects of lifestyle-related factors on the above associations. In this study, we included 30,521 subjects from the Dongfeng-Tongji (DFTJ) cohort and 25,761 subjects from the National Health and Nutrition Examination Survey (NHANES) 1999–2014. Cox proportional hazards regression models were used to estimate the associations of SII with mortality from all-cause, cardiovascular diseases (CVD), cancer and other causes. In the DFTJ cohort, compared to subjects in the low SII subgroup, those within the middle and high SII subgroups had increased risks of total mortality [hazard ratio, HR (95% confidence interval, CI) = 1.12 (1.03–1.22) and 1.26 (1.16–1.36), respectively) and CVD mortality [HR (95%CI) = 1.36 (1.19–1.55) and 1.50 (1.32–1.71), respectively]; those within the high SII subgroup had a higher risk of other causes mortality [HR (95%CI) = 1.28 (1.09–1.49)]. In the NHANES 1999–2014, subjects in the high SII subgroup had higher risks of total, CVD, cancer and other causes mortality [HR (95%CI) = 1.38 (1.27–1.49), 1.33 (1.11–1.59), 1.22 (1.04–1.45) and 1.47 (1.32–1.63), respectively]. For subjects with a high level of SII, physical activity could attenuate a separate 30% and 32% risk of total and CVD mortality in the DFTJ cohort, and a separate 41% and 59% risk of total and CVD mortality in the NHANES 1999–2014. Our study suggested high SII level may increase total and CVD mortality in the general populations and physical activity exerted a beneficial effect on the above associations.