Abstract MP86: The Joint Effect of Outdoor Recreational Activity and 25-Hydroxyvitamin D on Cardiovascular Mortality in THE NHANES III Population

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Purpose Recreational physical activity (PA) reduces the risk of cardiovascular disease (CVD) morbidity and mortality. Outdoor-based recreational physical activities (ORA) have been reported to be associated with elevated 25(OH)D levels. We investigate the joint effects of frequent ORA and 25(OH)D levels on the risk of CVD mortality and the modifying effects of 25(OH)D. Methods Our sample consisted of 13,031 nationally representative adults (20 - 90 years old) free from CVD and cancer at baseline in the NHANES III (1988 - 1994) linked mortality dataset with follow-up mortality data through 2006. CVD mortality was based on reported deaths with corresponding ICD-10 codes for CVD as underlying cause of death. ORA was defined as self-reported participation in recreational physical activities considered to have occurred outdoors in the past month. Time to CVD mortality was estimated from multivariable adjusted Cox proportional hazards (CPH) models. A joint effects model was used in estimating multiplicative and additive interaction between ORA and 25(OH)D. Results A crude unweighted CVD mortality rate of 7.4% (964/13,031) occurred during a median follow-up of 14.33 years. Frequency of ORA <5 in the past month (HR=1.38, 95%CI:1.09 - 1.75) and 25(OH)D <30 ng/mL (HR=1.28, 95%CI:1.01 - 1.60) were associated with increased risk of CVD mortality compared to ORA ≥5 and 25(OH)D ≥30 ng/mL respectively, in a multivariable adjusted CPH model. In the joint effects model, frequency of ORA <5 and 25(OH)D <30 ng/mL (HR=1.81, 95%CI:1.05 - 3.10) and frequency of ORA <5 and 25(OH)D ≥30 ng/mL (HR=1.33, 95%CI:1.02 - 1.73) were associated with elevated risk of CVD mortality compared to the joint effects of ORA ≥5 and 25(OH)D ≥30 ng/mL. The joint effects model indicated the presence of multiplicative interaction. The synergy index, 1.52 (95%CI:0.31 - 7.41) suggested presence of additive interaction even though not statistically significant. Conclusion Lower frequency of ORA and serum 25(OH)D levels were jointly associated with elevated risk of CVD mortality. Serum 25(OH)D modified the risk of CVD mortality associated with lower frequency of outdoor-based recreational activities.