The study, based on data from 9,611 older adults, shows that those who were regularly active in their 50s and early 60s were about 35 percent less likely to die in the next eight years than those who were sedentary. For those who had a high heart risk because of several underlying conditions, the reduction was 45 percent.
And the adults in the study didn't have to run marathons to get the death-reducing benefit: The reduction was seen even among those who walked, gardened, or went dancing a few times a week, as well as those who pursued more vigorous activities. Even those who were obese had a lower risk of dying if they were regularly active.
The results, published in the November issue of the journal Medicine and Science in Sports and Exercise, are from a study by researchers at the University of Michigan Medical School and the VA Ann Arbor Health Care System. It used data from the Health and Retirement study conducted by the U-M Institute for Social Research.
The findings suggest that efforts to get middle-aged people to exercise should pay special attention to those who have risk factors for cardiovascular disease or a history of heart attack or stroke.
It's the first prospective, nationally representative study to show that cardiovascular risk doesn't lessen exercise's impact on mortality risk. But it did confirm that those who have a high heart risk are much more likely to be sedentary, perhaps out of fear that exercising could overtax them.
"Other studies in smaller or less representative groups have shown the long-term benefits of exercise, even light exercise, but this study allowed us to look across different population groups, and different levels of cardiovascular risk, and see who got the most 'punch' out of exercise," says lead author Caroline Richardson, M.D., an assistant professor of family medicine at the U-M who performed the study when she was a Robert Wood Johnson Clinical Scholar at the U-M.
"We found that across all ranges of cardiovascular risk, everybody got a benefit from regular activity, but the biggest absolute benefit, the biggest reduction in deaths, was among high risk people," she adds.
The size of that effect surprised Richardson and her colleagues, including her RWJ mentor Rodney Hayward, M.D., senior author on the new paper and a professor of internal medicine at the U-M Medical School as well as a member of the Survey Research Center at the Institute for Social Research and director of the VA Center for Practice Management and Outcomes Research.
The result also convinced the authors that there needs to be a concerted effort to encourage exercise among currently sedentary people, especially those with cardiovascular risk factors.
"If we exclude high risk folks from studies or discourage them from being active, then we have lost the chance to make a big impact," says Richardson. "We need to prevent people from becoming part of that high risk group, by encouraging exercise as a way to lower their weight, blood sugar and blood pressure. But at the same time we need to address those at high risk now."
The research was based on HRS data for non-institutionalized adults born between 1931 and 1941, which Richardson calls an excellent, broad data source that represents the American population. Participants were first interviewed in 1992, and then again in 2000. At the initial interview, they were asked about their activity patterns, health characteristics, education and income levels, and other factors. They were contacted by survey staff yearly, and the current study was based on those who died from any cause during the years of the study, as verified through the National Death Index.
Of the 9,611 people studied, 15.2 percent led sedentary lives, engaging in light activity such as walking less than once a month. Housework was not included as an activity. Another 13 percent were classed as regularly active, taking part in moderate to vigorous exercise activities such as aerobics or bicycling at least three times a week. The rest were grouped as occasionally active.
The researchers also placed participants in one of three cardiovascular disease risk groups based on five characteristics: smoking, diabetes, high blood pressure, a history of coronary artery disease including heart attack and angina, and a history of stroke. Individually, each of these factors is known to increase the risk of death, but the risk is higher for those with more than one risk factor.
For the study, any participant with two or more risk factors was classed as having high cardiovascular risk - almost 22 percent of participants met this description. Those with one risk factor were considered moderate-risk, and those with no risk factors were considered low-risk.
In all, 810 participants died of any cause by the end of the study. The risk was, as expected, highest for those with high cardiovascular risk - they were more than four times as likely to die as low-risk participants. Moderate-risk participants were twice as likely as low-risk ones to die.
Even when the death tallies for each activity group were adjusted for age, sex, race, smoking, obesity, cancer history, overall health status, income, and heart risk, the results showed a protective effect from being regularly, moderately to vigorously physically active: a 38 percent lower death risk.
Combining activity level and heart risk level yielded even more interesting results. Almost 23 percent of those with high cardiovascular risk were sedentary, compared with 15 percent of moderate-risk adults and 11 percent of low-risk adults. Conversely, 33 percent of those who were sedentary had a high cardiovascular risk. And 27 percent of the sedentary, high-risk participants died by the end of the study -- almost twice the proportion of high-risk people in the study who were regularly active.
The researchers extrapolated those results to the entire U.S. population born in the same years as those in the study. They estimate that 3.52 million Americans in that age group lead sedentary lives, and that almost 228,000 of them would have died during the years of the study. Of those 228,000 deaths that might be attributed to a sedentary lifestyle, more than 146,000, or 64 percent, would be among those with high cardiovascular risk.
Although it's impossible to tell which came first, the heart risk or the lack of exercise, Richardson notes they go hand in hand -- especially among people with existing cardiovascular illnesses who cling to outdated beliefs that they shouldn't exercise because it might set off a heart attack. In fact, she says, the benefit of physical activity for most high cardiovascular disease-risk individuals probably outweighs the risks.
"For these people, the risk of having an acute problem brought on by exercise is small compared with the much higher risk of remaining sedentary," says Richardson. She is currently leading a VA-funded multicenter randomized controlled trial that will enroll veterans with cardiovascular risk factors and follow them for six months of walking using a pedometer, and diet and exercise counseling. She's also planning a study funded by the National Heart, Lung and Blood Institute that will use enhanced pedometers to encourage people with cardiovascular disease to walk.
In addition to Richardson and Hayward, the study's authors were Andrea Kriska, Ph.D., of the University of Pittsburgh School of Public Health, and Paula Lantz, Ph.D., of ISR and the U-M School of Public Health. Hayward also holds an appointment in the U-M School of Public Health.
The Health and Retirement Study was funded by the National Institute on Aging. The analysis published in the current paper was partially supported by the Robert Wood Johnson Clinical Scholars Fellowship Program at the University of Michigan and by the Veterans Administration Health Services Research and Development Unit at the VA Ann Arbor Health Care system.
Reference: Medicine & Science in Sports & Exercise (American College of Sports Medicine), November 2004, Volume 36, Issue 11, pp. 1923-1929.