Increased Fitness, Not Weight Loss, Improves Mortality

December 05, 2011

December 5, 2011 (Columbia, South Carolina) — Good news for exercise junkies who don't quite look like all-American swimmer Michael Phelps or the ultralean marathoners crossing the New York City finish line: Fitness appears to trump weight loss when it comes to reducing all-cause and cardiovascular mortality [1]. Data from a large longitudinal study show that maintaining and improving physical-fitness levels were associated with lower risks of all-cause and cardiovascular disease mortality, whereas changes in body-mass index (BMI) were not.

In addition, the researchers observed that men who lost physical fitness over an 11-year follow-up period had a significantly higher risk of cardiovascular death regardless of changes in BMI when compared with men who remained unfit.

"To date, extensive attention has been given to weight loss," states Dr Duck-chul Lee (University of South Carolina, Columbia) and colleagues in the study, published online December 5, 2011 in Circulation. "However, the long-term effect of fitness change, primarily resulting from increasing physical activity, is likely to be at least as important as weight loss for reducing premature mortality. Increased attention needs to be placed on strategies to maintain or improve fitness."

To heartwire , Lee noted that approximately 90% of patients included in the analysis were overweight or obese, so it remains unknown if the same results would be observed in patients with lower BMIs. In those populations, for example, weight gain in healthy-weight patients might play a more important role and be associated with an increased risk of mortality.

"But I do think that if individuals can maintain or improve their fitness levels, they need to worry less about weight gain," said Lee. "People really think that weight gain is a bad thing, but in our study fitness loss was associated with a higher risk of mortality regardless of weight change."

Reducing Mortality 15% for Every 1-MET Improvement

Cardiorespiratory fitness, expressed in metabolic equivalents (METs), is a strong independent predictor of mortality. In addition, BMI, the most used marker of obesity, is also strongly predictive of mortality, with most associations between BMI and mortality either J-shaped or U-shaped. The studies that established the relationship between BMI, fitness, and mortality typically assessed the measures at baseline and assumed no change over follow-up.

Using data from the Aerobics Center Longitudinal Study, the combined association of changes in fitness and BMI on overall and cardiovascular mortality were assessed in 14 435 men with at least two medical evaluations and an average follow-up of 11.4 years since the last examination. Changes in fitness and BMI, which occurred over a six-year period, were recorded as a loss, as stable, or as a gain.

In a multivariable analysis adjusted for multiple risk factors, including changes in BMI, men who maintained their physical-fitness levels had a 30% and 27% lower risk of death and cardiovascular death, respectively, when compared with men who lost fitness. Those who got into better shape from baseline had a 39% and 42% lower risk of death and cardiovascular mortality, respectively, when compared with those who lost fitness over the years. Every 1-MET improvement resulted in a significant 15% reduction in the risk of death and a 19% reduction in the risk of cardiovascular disease mortality.

BMI changes, on the other hand, were not significantly associated with all-cause mortality, but men who gained weight had a 39% higher risk of cardiovascular disease mortality compared with men who lost weight, although the association was attenuated and no longer statistically significant when adjusted for maximal MET changes. One BMI unit increase was associated with a borderline increase in all-cause and cardiovascular disease mortality, but the association was not significant in a risk model that adjusted for maximal MET changes.

Hazard Ratios of All-Cause Mortality and Cardiovascular Disease Mortality by Changes in Fitness and BMI

Variable All-cause mortality, hazard ratio (95% CI) Cardiovascular disease mortality, hazard ratio (95% CI)
Fitness change, loss 1.00 1.00
Fitness change, stable 0.70 (0.59–0.83) 0.73 (0.54–0.98)
Fitness change, gain 0.61 (0.51–0.73) 0.58 (0.42–0.80
p for trend <0.001 <0.001
Per 1-MET increase 0.85 (0.80–0.89) 0.81 (0.74–0.89)
BMI, loss 1.00 1.00
BMI, stable 1.06 (0.90–1.26) 0.98 (0.71–1.34)
BMI, gain 1.03 (0.87–1.23) 1.26 (0.94–1.69)
p for trend 0.68 0.14
Per 1-BMI increase 1.03 (0.98–1.08) 1.06 (0.97–1.14)

*Adjusted for age, examination year, parental cardiovascular disease, BMI, and maximal METs at baseline; the combination patterns of each lifestyle factor (smoking status, alcohol intake, and physical activity) and each medical condition (abnormal electrocardiogram, hypertension, diabetes, and hypercholesterolemia) at the baseline and last examinations; adjusted for the number of clinic visits between the baseline and last examinations; and adjusted for BMI change (for fitness) and maximal MET change (for BMI) between baseline and last examination

Men who became or remained fit had a significant 47% and 48% lower risk of all-cause mortality, respectively, compared with men who remained unfit. Similarly, men who became or remained fit had a 41% and 44% lower risk of cardiovascular disease mortality, respectively. Interestingly, men who lost cardiorespiratory fitness had a nearly twofold increased risk of cardiovascular disease mortality (hazard ratio 1.89; 95% CI 1.03–3.45) compared with men who remained unfit.

In contrast, changes in BMI status were not associated with mortality after adjustment for potential confounders, including changes in fitness. For example, becoming normal weight did not appear to have any benefit in terms of reducing the risk of all-cause and cardiovascular death, while becoming overweight did not appear to increase the risk of mortality. Lee noted that men who increased their physical-activity levels were significantly more likely to maintain their cardiorespiratory-fitness levels, adding that 80% of men who maintained their fitness levels increased their physical-activity levels.

"Basically, to increase or maintain fitness levels, physical activity is the most important factor that people can modify," said Lee.

The researchers note that overweight or obese persons make up two-thirds of the US population, but focusing on improving fitness, especially given how difficult it is for some patients lose weight and maintain weight loss over the long term, could have important clinical and public-health implications.


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