A new study of 14,345 adult men, published in Circulation, a Journal of the American Heart Association, found that improving physical fitness lowered risk of death, both from cardiovascular disease and from all causes, even after controlling for body weight (BMI) change. On the other hand, change in body weight (BMI) alone was not associated with any change in death risk according to the findings of this study.
The new study, by scientists from the University of South Carolina School of Public Health, Harvard Medical School and several other institutions, is published in the December 5 issue of Circulation, a Journal of the American Heart Association.
Participants in the study included 14,345 adult men, who were an average 44 years old, mostly white and middle or upper class. The men were part of a long-term, large-scale “Aerobics Center Longitudinal Study.” The men underwent at least two comprehensive medical exams as part of the study.
Researchers used maximal treadmill tests to estimate physical fitness (maximal METs), and height and weight measurements to calculate Body Mass Index (BMI). MET measures the intensity of aerobic exercise – specifically, the ratio of metabolic rate during a specific physical activity to a reference rate of metabolic rate at rest. BMI is a measure of body weight relative to height. A BMI score under 25 is considered healthy, 25 to less than 30 is overweight, and 30 or greater is obese.
The researchers recorded changes in physical fitness and in BMI over 6.3 years.
“Changes in fitness and BMI between the baseline and last examinations over 6.3 years were classified into loss, stable, or gain groups,” the researchers explained.
During 11.4 years of follow-up after the last examination, a total of 914 of the participants died. Of these, 300 deaths were caused by cardiovascular disease.
The researchers performed statistical analysis to determine whether the relative risks of dying from all causes or from cardiovascular disease were different for those with stable fitness or fitness gain, compared to those with fitness loss. A similar analysis was done with respect to BMI change.
In their analysis of the association between fitness and risk of dying, they controlled for other factors that could affect outcomes, including BMI change, age, family history of heart disease, beginning fitness level, changes in lifestyle factors such as smoking and physical activity, and medical conditions such as high blood pressure or diabetes.
After controlling for the other factors referenced, the researchers found that, compared to those who lost fitness, the participants who maintained stable fitness had a 30% lower risk of dying of any cause and a 27% lower chance of dying from cardiovascular disease. Participants who gained in fitness during the study had a 39% lower risk of dying of any cause and a 42% lower risk of dying of cardiovascular disease.
Every unit of increased fitness (measured as MET, metabolic equivalent of task) over six years was associated with a 19 percent lower risk of heart disease and stroke-related deaths and a 15 percent lower risk of death from any cause, the researchers reported.
On the other hand, “BMI change was not associated with all-cause or CVD [cardiovascular disease] mortality after adjusting for possible confounders and fitness change,” the researchers found. “In the combined analyses, men who lost fitness had higher all-cause and CVD mortality risks regardless of BMI change.” Thus, becoming less fit was linked to higher death risk, regardless of BMI changes.
Stated in scientific terms, the study authors summarized their findings as follows:
Maintaining or improving fitness was thus associated with a lower death risk even after controlling for Body Mass Index (BMI) change, while becoming less fit was associated with higher death risk, regardless of BMI changes.
In conclusion, the study authors wrote, “Maintaining or improving fitness is associated with a lower risk of all-cause and CVD [cardiovascular disease] mortality in men. Preventing age-associated fitness loss is important for longevity regardless of BMI change.”
The results of the study underscore the importance of physical inactivity as a risk factor for death from heart disease and stroke, the researchers said. In fact, physical fitness was more important than weight control, according to this study, which found no association between changes in body fat percentage or body weight and death risk.
“This is good news for people who are physically active but can’t seem to lose weight,” said Duck-chul Lee, Ph.D., the study’s lead researcher and physical activity epidemiologist in the Department of Exercise Science at the University of South Carolina’s Arnold School of Public Health in Columbia. “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”
Dr. Lee, the study’s principal author, however, did explain that one possible explanation for the study results could be that about 90 percent of the men were either normal weight or overweight at the beginning of the study. Among obese people, changes in BMI might have a significant effect on death risks. So it’s unclear whether these results would apply to severely obese people, Dr. Lee said.
Because the study was mostly done in white middle and upper class men, it’s difficult to know whether the results apply to other racial and socioeconomic groups. Women would likely have similar results as the men in the study, Dr. Lee said.
The study report is found in the December 5 issue of Circulation, a Journal of the American Heart Association.
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