Trends in multimorbidity among US adults and the correlation between physical activity and mortality: Prospective cohort study from 1999 to 2018

Evidence regarding the mortality risk associated with physical activity (PA) and multimorbidity is limited. This study investigates trends in the prevalence of multimorbidity in the population and the mortality risk associated with PA and multimorbidity. The association between PA and overall survival was analyzed in 39,940 subjects from the National Health and Nutrition Examination Survey cohorts. Among the 39,940 participants (weighted average age: 46.84; 50.86% female), the age-standardized prevalence of multimorbidity rose significantly, from 15.87% (95% confidence interval [CI] = 14.86%-16.87%) in 1999 to 2000 to 19.96% (95% CI = 17.61%-22.32%) in 2017 to 2018. The population's multimorbidity detection rate was 25.22%. The all-cause mortality risks for multimorbidity were: dual-multimorbidity (hazard ratio [HR] = 1.97, 95% CI = 1.76-2.20), triple-multimorbidity (HR = 2.69, 95% CI = 2.35-3.08), quadruple-multimorbidity (HR = 3.22, 95% CI = 2.59-3.99). "Diabetes mellitus + cardiovascular disease + respiratory diseases" had the highest mortality risk (HR = 4.37, 95% CI = 2.67-7.16). PA reduced all-cause and cause-specific mortality, with moderate-intensity PA lowering all-cause mortality by 22% compared to low-intensity PA, and high-intensity PA by 6% compared to moderate-intensity PA. Multimorbidity led to a 5.64 years life expectancy loss, while PA could recover up to 2.31 years. PA potentially recouped 2.96 and 2.19 years of life lost due to comorbidity in females and males, respectively. According to National Health and Nutrition Examination Survey data from 1999 to 2000 to 2017 to 2018, multimorbidity prevalence increased. PA reduces all-cause mortality by 32%. Greater PA intensity correlates with more significant mortality reduction. Multimorbidity cuts life expectancy by 5.64 years, recoverable by PA (2.31 years). Females regain 2.96 years; males, 2.19 years.