Observational studies in older adults have found that physical activity is correlated with a number of measures of health, including increased strength and flexibility, increased aerobic capacity, improved balance and fewer falls, a reduced decline in bone density, improved glucose metabolism and insulin sensitivity, enhanced emotional well-being, and a reduced decline in cognitive function (Steptoe and Wikman, 2010). It should be noted, however, that drawing conclusions about the link between physical activity in older adults and health based on observational studies is somewhat hazardous because individuals can self-select into various states of physical activity. This selection is likely to be affected by their health. For example, people with chronic obstructive lung disease may be less likely to engage in vigorous activities. Both their high relative mortality risk and their low levels of exercise would likely be attributable to preexisting disease rather than to any effect of physical activity on mortality. It is also true that people with certain characteristics and behaviors (e.g., being poor and smoking) may be both less likely to exercise and more likely to be unhealthy. This section reviews the results from the large number of observational studies that have attempted to quantify the benefits of physical activity for older adults. The following section describes the far fewer studies that have used a randomized design to assign people to levels of activity.
Hamer and Chida (2008) performed a meta-analysis of 18 prospective studies that looked at the effects of walking on the risk of cardiovascular disease. The likelihood of developing cardiovascular disease was 31 percent lower among the group that walked the most compared with the group that walked the least. The benefits of walking were similar for men and women, and greater benefit came from walking briskly rather than from walking for longer periods of time. There was also some evidence of a dose–response relationship—that is, the more walking people did, the more it decreased their risk of developing cardiovascular disease.
In a subsequent review, the same authors examined the effects of physical activity on neurodegenerative diseases, such as dementia and Alzheimer’s disease (Hamer and Chida, 2009). Based on a meta-analysis of 16 prospective studies, they found that people in the highest physical activity category were 28 percent less likely to develop dementia and 45 percent less likely to develop Alzheimer’s disease than those in the lowest physical activity category. There is also good evidence that older adults who exercise are less likely to become depressed. Hamer and colleagues (2009) followed 4,300 older men and women (average age of 63) for 4 years. None reported symptoms of depression at the beginning of the study, while 8 percent did so 4 years later. The authors found that the people who reported engaging in regular, moderate physical activity were 29 percent less likely to develop