The Potential Mediating Effects of Social Support Network Size and Physical Activity on Cognitive Function and Mortality Risk

BACKGROUND: Low cognitive function has been shown to be an independent predictor of all-cause and cardiovascular disease (CVD)-related mortality. Social support network size and total physical activity volume (TPAV) are two modifiable factors which have been shown to be independently associated with cognitive function and mortality risk. Therefore, the purpose of this study was to examine the potential mediating effects of social support network size and TPAV on cognitive function and all-cause and CVD-related mortality risk in a large, nationally representative sample of U.S. adults. METHODS: Study sample (N =2,550) included older adult (≥ 60 years of age) participants in the 1999-2002 National Health and Nutrition Examination Survey. Quartiles of cognitive function were created using Digit Symbol Substitution Test scores. Social support network size was determined using the number of reported close friends. TPAV was determined from self-reported domestic, transportation, and leisure time physical activity. RESULTS: Regression analysis revealed an approximate three-fold increase in all-cause and CVD-related mortality risk in participants in the lowest quartile of cognitive function, compared to the highest quartile of cognitive function. These relationships are independent of social support network size and TPAV. Linear and non-linear inverse dose-response relationships were also revealed between cognitive function and increased all-cause and CVD-related mortality risk, respectively (P for trend for both P \u3c 0.0001). CONCLUSION: In a large, nationally representative sample of U.S. older adults, low cognitive function was associated with increased all-cause and CVD-related mortality risk. However, both relationships were independent of social support network size and TPAV