Researchers in Sweden have found an association between a person’s fitness as a teenager and their risk of heart attack in later life. In a study of nearly 750,000 men, they found that the more aerobically fit men were in late adolescence, the less likely they were to have a heart attack 30 or 40 years later.
The study, published online today (Wednesday) in the European Heart Journal, found that the relationship between aerobic fitness and heart attack occurred regardless of the men’s body mass index (BMI) when they were teenagers. However, fit but overweight or obese men had a significantly higher risk of a heart attack than unfit, lean men.
Professor Peter Nordström, of Umeå University, Umeå, Sweden, who led the research, said: “Our findings suggest that high aerobic fitness in late adolescence may reduce the risk of heart attack later in life. However, being very fit does not appear to fully compensate for being overweight or obese in respect to this risk. Our study suggests that it’s more important not to be overweight or obese than to be fit, but that it’s even better to be both fit and a normal weight.”
Prof Nordström and his colleagues analysed data from 743,498 Swedish men who underwent medical examinations at the age of 18 when they were conscripted into the Swedish armed forces between 1969-1984. Aerobic fitness was measured by a cycle test where the resistance was gradually increased until they were too exhausted to continue.
The researchers found that every 15% increase in aerobic fitness was linked to an approximately 18% reduced risk of a heart attack (myocardial infarction or MI) 30 years later after adjusting for various confounding factors including socioeconomic background and BMI. The results also suggested that regular cardiovascular training in late adolescence was independently associated with an approximately 35% reduced risk of an early heart attack in later life.
“There were 7,575 myocardial infarctions in 620,089 men during the total follow-up time where aerobic fitness was measured, which means the cumulative incidence was about 1222 per 100,000 men,” explained Prof Nordström. “There were 271,005 men (43.7%) who were normal weight or lean, and who had an aerobic fitness that was better than the average. Among these lean, fit men there were 2176 MIs, resulting in a cumulative incidence of about 803 MIs per 100,000 men. Thus, the cumulative incidence of MIs was reduced by about 35% in this group.”
However, he warned that the study showed only that there was an association between fitness and a reduction in heart attacks, and it could not show that being aerobically fit caused the reduced risk of heart attack.
“The relationship between aerobic fitness and heart disease is complex and may well be influenced by confounding factors that were not investigated in this study. For instance, some people may have a genetic predisposition to both high physical fitness and a low risk of heart disease. In a recent study of twins, we found that 78% of the variation in aerobic fitness at the time of conscription is related to genetic factors.”
At the time of the men’s conscription they had a full medical examination, which included checking blood pressure, weight, height and muscle strength, as well as aerobic fitness. During the cycle test for aerobic fitness, the resistance was gradually increased at the rate of 25 watts a minute until the men were too exhausted to continue. The final work rate (maximum watts) was used for the analysis. The average work rate for the men was 250 watts.