Diabetes and Exercise

Exercise and Primary Prevention

The first systematic investigation on the effect of regular physical exercise as a protective factor against coronary artery disease was published more than 60 years ago (1).

It showed a negative correlation between the amount of physical work performed and the incidence of myocardial infarction in London bus drivers. Since then this finding has been confirmed by a great number of studies conducted on thousands of patients.

More than 3000 healthy, nondiabetic volunteers participated in the U.S. railroad study, which established a linear, inverse relation between the amount of energy spent during leisure time physical activity and the risk to develop coronary artery disease (2).

The lowest risk was calculated for the most active persons who consumed more than 3000 kcal/week, which requires roughly 6 hours of training at medium intensity. The optimal level of intensity has been a matter of considerable controversy and contradictory recommendations.

In the U.S. railroad study 100 kcal/week spent in the form of intensive exercise weighed as much as 1000 kcal/week of moderate exercise with regard to its protective effect, i.e., intensive physical exercise was 10 times more effective than moderate exercise, whereas walking was associated with beneficial effects in other trials (3, 4).

An interesting trial has been published under the name Harvard Alumni study (5); in 16,936 college alumni the amount of leisure time physical activity was estimated from questionnaires and structured interviews.

After an observation time between 12 and 16 years participants in the most active group reduced their cardiovascular risk by 50% as compared to inactive persons. All of the above studies determined physical activity by questionnaire with an inherent degree of error.

A recently published trial used the maximal work capacity on a treadmill to determine "physical fitness" as a hard parameter in more than 6000 patients referred for evaluation of various angina-like symptoms. Cardiovascular risk in the fittest quintile was only one-quarter of the risk in the quintile with the lowest fitness (6).

In total there are more than 30 publications with nearly 250,000 enrolled patients, followed for an average of 10 years, documenting the efficacy of regular physical exercise to reduce cardiovascular risk in primary prevention.

Accordingly the ACC/AHA task force on primary prevention determined that there is sufficient evidence to make exercise a class I recommendation for primary prevention of coronary artery disease without the need for further studies in this field.