Aerobic Fitness in Youth Linked With Lower MI Risk Later in Life

January 07, 2014

UMEÅ, SWEDEN — High levels of aerobic fitness in late adolescence translated into a significantly lower risk of MI later in life, according to the results of a new Swedish study[1]. Each standard-deviation (SD) increase in aerobic workload was associated with nearly a 20% reduction in the risk of MI, report investigators.

"Aerobic fitness is not the same as physical activity," senior research Dr Peter Nordström (Umeå University, Sweden) told heartwire . "Physical fitness is basically how long you can run on the treadmill before you fall off. It's how long and how fast you can go and it's determined by genetic factors. So in this study, we have estimated the amount of physical fitness, which is attributed to an individual's genes. A lot of the variation in physical fitness is attributed to genetics."

Published online January 8, 2014 in the European Heart Journal, the large cohort study included 743 498 Swedish men 18 years of age who were conscripted into military service between 1969 and 1984. All individuals underwent aerobic fitness testing using an electrically braked ergometer cycling test that increased resistance until the point of fatigue.

After a mean follow-up of 34 years, there were 11 526 men diagnosed with MI. After adjustment for age, body-mass index (BMI), blood pressure, and socioeconomic factors, among other variables, each SD increase in the maximal work rate, which was used as a marker of aerobic fitness, decreased the risk of MI by 18%. Compared with men in the highest quintile, those with the lowest levels of aerobic fitness had a more than twofold increase in risk. There was no association between muscle-strength measurements at baseline and later risk of MI.

The researchers report that the association between aerobic fitness and cardiac risk was evident across all BMI groups. However, obese and overweight men considered physically fit still had a higher risk of MI than lean or normal-weight unfit men.

To heartwire , Nordström says the results must be interpreted with a lot of caution. He said it is not known what effect physical fitness, per se, had on the long-term outcomes vs the underlying genes that might contribute to physical fitness and a lower lifetime risk of MI.

"There could also be confounding, even though we adjusted for a number of variables at baseline," he said. "But it's one thing with a statistical model and another in real life. We really don't know what can be attributed to the effect of higher physical fitness and the risk of myocardial infarction. . . . In this case, we have 30 years of follow-up, and there is a lot going on in these years that we don't know about. People that didn't train a lot might start training, and those that trained a lot might stop training, and that would indeed affect physical fitness."

The authors report no conflicts of interest.

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