Maintaining or improving level of fitness can still reduce a person's risk of death even if body mass remains unchanged. That's according to a new study that suggests physical fitness has a greater impact on health than does body mass index alone.

The study¹,  finding of which were reported in Circulation: Journal of the American Heart Association, followed 14,345 adult males for a period of six years. Results showed that that maintaining or improving fitness was associated with a lower death risk even with a control for Body Mass Index (BMI) change.

The study sought to examine independent and combined associations of changes in fitness and BMI with all-cause and cardiovascular disease mortality.

The two key measurements in the study were BMI (a measurement based on weight and height (kg/m²) and metabolic equivalent of task (MET), recorded as units of increased fitness. MET measures the intensity of aerobic exercise, in particular, the ratio of metabolic rate during a specific physical activity to a resting metabolic rate as reference. A BMI score under 25 is deemed healthy, 25 to less than 30 is overweight, while 30 or over is obese.

Maximal treadmill tests were used to gauge physical fitness (maximal METs), along with height and weight measurements to arrive at BMI. In addition, each participant underwent at least two comprehensive medical exams.

Results showed that each 1-MET unit was associated with a 19 percent lower risk of heart disease and stroke-related deaths, along with a 15 percent lower risk of death from any causes.

Conversely, results showed that growing less fit was associated with a higher death risk, even without taking into account any BMI changes; BMI change itself was not associated with death risks, the study found. The researchers also found no association between changes in body fat percentage or body weight and death risk.

Results of the study point to the importance of physical inactivity as a risk factor for death from cardiovascular disease, according to the researchers.

After over 11 years of follow-up, researchers determined the relative risks of dying among men who lost, maintained or gained fitness over the course of the study. The researchers accounted for other factors that could have effects on results, such as BMI change, age, a family history of heart disease, fitness level at the beginning of the study, any changes in lifestyle factors like smoking and physical activity, as wells as medical conditions including as high blood pressure or diabetes.

The authors noted that one potential limitation of the results are their applicability to those who fall in the obese category or are among other racial and socioeconomic groups than the primarily Caucasian, middle- and upper-class men studied: The average age of participants was 44, while approximately 90 percent of the men were either normal weight or overweight at the outset of the study. 

Source:

1. Long-Term Effects of Changes in Cardiorespiratory Fitness and Body Mass Index on All-Cause and Cardiovascular Disease Mortality in Men: The Aerobics Center Longitudinal Study. Circulation., 2011; 124: 2483-2490 DOI: 10.1161/CIRCULATIONAHA.111.038422

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