Exercise and Type 2 Diabetes
The possible benefits of exercise for the patient with type 2 diabetes are substantial and recent studies strengthen the importance of long term exercise programs for the treatment and prevention of this common metabolic abnormality and its complications. Specific metabolic effects can be highlighted as follows.
Several long term studies have demonstrated a consistent beneficial effect of regular exercise training on carbohydrate metabolism and insulin sensitivity which can be maintained for at least five years. These studies used exercise regimens at an intensity of 50-80% VO2 max three to four times a week for 30-60 minutes a session. Improvements in HbA1c were generally 10-20% of baseline and were most marked in patients with mild type 2 diabetes and those who are likely to be the most insulin resistant. It remains true, unfortunately, that most of these studies suffer from inadequate randomization and controls, and are confounded by associated lifestyle changes. Data on the effects of resistance exercise are not available for type 2 diabetes although early results in normals and patients with type 1 disease suggest a beneficial effect.
It now appears that long term programs of regular exercise are indeed feasible for patients with impaired glucose tolerance or uncomplicated type 2 diabetes with acceptable adherence rates. Those studies with the best adherence have used an initial period of supervision followed by relatively informal home exercise programs with regular frequent follow up assessments. A number of such programs have demonstrated sustained relative improvements in VO2 max over many years with little in the way of significant complications.
Prevention of Cardiovascular Disease
In patients with type 2 diabetes, the Insulin Resistance Syndrome continues to gain support as an important risk factor for premature coronary disease, particularly with concomitant hypertension, hyperinsulinemia, central obesity, and the overlap of metabolic abnormalities of hypertriglyceridemia, low HDL, altered LDL, and elevated FFA. Most studies show that these patients have a low level of fitness compared to controls even when matched for levels of ambient activity and that the poor aerobic fitness is associated with many of the cardiovascular risk factors. Improvement in many of these risk factors has been linked to a decrease in plasma insulin levels and it is likely that many of the beneficial effects of exercise on cardiovascular risk are related to improvements in insulin sensitivity.
Regular exercise has consistently been shown to be effective in reducing levels of triglyceride-rich very low density lipoprotein (VLDL). However, effects of regular exercise on levels of LDL cholesterol have not been consistently documented. With one major exception most studies have failed to demonstrate a significant improvement in levels of HDL in patients with type 2 diabetes, perhaps because of the relatively modest exercise intensities used.
There is evidence linking insulin resistance to hypertension in patients. Effects of exercise on reducing blood pressure levels have been demonstrated most consistently in hyperinsulinemic subjects.
Many patients with type 2 diabetes have impaired fibrinolytic activity associated with elevated levels of Plasminogen Activator Inhibitor-I (PAI-1), the major naturally occurring inhibitor of Tissue Plasminogen Activator (TPA). Studies have demonstrated an association of aerobic fitness and fibrinolysis. There is still no clear consensus on whether physical training results in improved fibrinolytic activity in these patients.
Data have accumulated suggesting that exercise may enhance weight loss and in particular weight maintenance when used along with an appropriate calorie-controlled meal plan. There are few studies specifically dealing with this issue in type 2 diabetes and much of the available data is complicated by the simultaneous use of unusual diets and other behavioral interventions. Of particular interest are studies suggesting a disproportionate effect of exercise on loss of intra-abdominal fat, the presence of which has been associated most closely with metabolic abnormalities. Data on the use of resistance exercise in weight reduction are promising, but studies in patients with type 2 diabetes in particular are lacking.
Prevention of Type 2 Diabetes
A great deal of evidence has been accumulated supporting the hypothesis that exercise, among other therapies, may be useful in preventing or delaying the onset of type 2 diabetes. Currently a large randomized prospective NIH study is under way to clarify the feasibility of this approach.
Cite this: Diabetes Mellitus and Exercise - Medscape - Dec 01, 1997.