Natural history of leisure-time physical activity and its correlates: associations with mortality from all causes and cardiovascular disease over 28 years.

The association between leisure-time physical activity and 28-year (1965-1993) risk of death from all causes and cardiovascular disease was studied in 6,131 adults who participated in the Alameda County Study in Northern California. Because study participants were interviewed on a number of occasions, it was possible to include in the analyses information on changes over time in levels of leisure-time physical activity as well as changes in a wide variety of other risk factors. There were 47,616 person-years of observation for males (639 deaths from all causes and 321 from cardiovascular disease) and 57,666 person-years of observation for females (587 deaths from all causes and 388 from cardiovascular disease). In analyses in which only the baseline values of all covariates were included, a four-point increase on the leisure-time physical activity scale, the interquartile range, was associated with reduced risk of death from all causes (relative risk (RR) = 0.90, 95% confidence interval (CI) 0.83-0.99) and cardiovascular disease (RR = 0.85, 95% CI 0.75-0.97). When time-varying information on leisure-time physical activity and all other covariates was included, there was still a protective effect for all-cause and cardiovascular disease mortality (RR = 0.84, 95% CI 0.77-0.92 and RR = 0.81, 95% CI 0.71-0.93, respectively). The association between leisure-time physical activity and risk of death was not altered when information on variations over time in leisure-time physical activity and many determinants and consequences of physical activity were explicitly included in survival models.