Physical activity and diabetes
Ralph Hall, MD
Emeritus Professor of Medicine
School of Medicine
University of Missouri-Kansas City
(Commentary from Diabetes Management Consulting Editor)
It has been conclusively demonstrated that exercise can delay the onset of arteriosclerotic vascular disease and reduce the morbidity and mortality from heart attack and stroke. It has also been demonstrated that physical activity can delay, and most likely prevent, the onset of Type 2 diabetes in some patients.
The benefits of physical activity have not been as conclusively documented for Type 1 diabetes. However, the favorable effects of exercise on cardiovascular risk factors such as blood pressure, lipoproteins, and clotting factors show that exercise may reduce cardiovascular morbidity and mortality in patients with Type 1 diabetes.
Hein et al1 demonstrated that physical activity was a greater predictor of ischemic heart disease (IHD) than physical fitness and that the benefits were dose-related. The more frequent and more intense the exercise, the greater the reduction in IHD. Lee and Paffenbarger point out, "Physical activity is an optional activity, while physical fitness is an achieved condition.
Physical activity modifies physical fitness over time, whereas physical fitness limits the amount of physical activity that can be performed."2 Thus, physical activity and physical fitness each may act independently to increase longevity and reduce morbidity.
The study by Hein’s group involved 4,999 men ages 40 to 59 and lasted 17 years. This study removed one of the criticisms that physical fitness, which has a strong genetic component, made it difficult to conclude that physical activity decreased the occurrence of cardiovascular disease. Critics claimed that those who were genetically fit tended to exercise and benefited more from exercise. Hein’s studies, however, showed that less fit men who exercised had less cardiovascular disease than fit men who were sedentary. In another report by Sandvik et al, it was also found that there was a dose-response relationship. It also pointed out that the dose-response relationship could not have been detected if the study had been carried out for fewer than 10 years.3
Blair and others,4 have demonstrated that moderate physical activity can markedly reduce the incidence of cardiovascular morbidity and mortality. This was true even though the exercise program was begun during middle age in unfit subjects.
When the guidelines for physical activity were released by the Centers for Disease Control and Prevention and The American College of Sports Medicine, a controversy immediately erupted.
The recommendations from these two organizations was for moderate exercise. Paul Williams of The Lawrence Berkeley National Laboratory in Berkeley, CA, and Paul Thompson, MD, of Hartford (CT) Hospital, both noted authorities in the field of exercise science, were concerned that too little exercise was being recommended. A review in Science, in which they were quoted,5 noted the dilemma. "Recommend too vigorous a regimen and people may be scared off; Recom mend easier goals and many may be deterred from getting the full benefits of exercise."
Two recent publications have demonstrated that there are many benefits to a program of moderate exercise, confirming the results of Blair et al.6,7
Improvements in cardiovascular risk factors occurred in both structured programs and in people who increased their activity through lifestyle changes in physical activity such as walking, climbing stairs, etc. The use of moderate physical activity, in the opinion of many experts, is more likely to elicit greater overall benefit. Those who wish to do more, however, should be encouraged to do so.
Endurance exercise has been the principal activity emphasized in the past as having the greatest benefit. Recent research indicates, however, that there is much benefit to be gained from resistance exercise. Resistance exercise has been shown to favorably effect insulin resistance, weight gain, lipoproteins, bone density, and other cardiovascular risk factors. It will correct many of the effects of aging by improving balance, strength, and increased muscle mass. Those with the least strength have the greatest percentage increase in strength in only a few weeks.8
There is much to be gained using an exercise program that includes all three elements of exercise:
1. resistance training;
2. aerobic exercise;
3. stretching.
It is the responsibility of all of us who work with patients with diabetes to be current in our knowledge of the benefits of exercise, as well as the potential risks. This knowledge is especially important if we are to safely manage older Type 2 diabetics and diabetics with neurologic and cardiovascular complications.
References
1. Hein HO, et al. Physical fitness or physical activity as a predictor of ischemic heart disease? A 17-year follow-up in the Copenhagen Male Study. J Intern Med 1992; 232:471-479.
2. Lee I, Paffenbarger RS. Do physical activity and physical fitness avert premature mortality? Exerc Sport Sci Rev 1996; 24:135-171.
3. Sandvik L, Erikssen J, Thaulow E, et al. Physical fitness as a predictor of mortality among healthy, middle-aged Norwegian men. N Engl J Med 1993; 328:533-537.
4. Blair SW, et al. Physical fitness and all-cause mortality: A prospective study of healthy men and women. JAMA 1989; 262:2,395-2,401.
5. Barinaga M. How much pain for cardiac gain? Science 1997; 276:1,324-1,327.
6. Dunn A, Marcus B, Kampert J, et al. Comparison of lifestyle and structured interventions to increase physical activity and cardiovascular fitness: A randomized trial. JAMA 1999; 281:327-334.
7. Anderson R, Wadden T, Bartlett S, et al. Affects of lifestyle activity vs. structured aerobic exercise in obese women: A randomized trial. JAMA 1999; 281:335-340.
8. Evans WJ. Exercise training guidelines for the elderly. Med Sci Sports Exerc 1999; 31:12-16.
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