ROLE OF PHYSICAL EXERCISE, FITNESS AND AEROBIC TRAINING IN TYPE 1 DIABETIC AND HEALTHY MEN IN RELATION TO THE LIPID PROFILE, LIPID PEROXIDATION AND THE METABOLIC SYNDROME

Dyslipidemia and possibly lipid peroxidation play important roles in the development of macroand microvascular disease in type 1 diabetes mellitus. Little is known, however, of the role of aerobic exercise in dyslipidemia and resting and exercise-induced lipid peroxidation in type 1 diabetes. Despite the wellknown effect of leisure-time physical activity (LTPA) on components of the metabolic syndrome, little is known of the association of LTPA and cardiorespiratory fitness (maximal oxygen consumption, VO2max) with development of the metabolic syndrome itself. A randomized controlled trial assessing the effect of a 12-16 week aerobic exercise program on VO2max and the lipid profile was carried out in otherwise healthy young men with type 1 diabetes. The effect of acute physical exercise on oxidative stress and antioxidant defenses and the relation to VO2max in men with type 1 diabetes was also evaluated. To test four recently proposed definitions by the World Health Organization (WHO) and National Cholesterol Education Program (NCEP) of the metabolic syndrome, the sensitivity and specificity of the definitions for prevalent and incident diabetes were assessed in a population-based cohort of middle-aged men. We also studied the associations of LTPA and cardiorespiratory fitness with prevalent and incident cases of the metabolic syndrome. A 12-16 week endurance exercise program produced antiatherogenic changes in lipid, lipoprotein and apolipoprotein levels in 20 type 1 diabetic men who for the most part were already physically active at baseline. The most favorable training-induced changes in the high-density lipoprotein cholesterol (HDL)/low-density lipoprotein cholesterol (LDL) and apolipoprotein A-I/apolipoprotein B ratios were in patients with low baseline HDL/LDL levels, likely the group with the most benefit to be gained by such changes. Plasma thiobarbituric acid reactive substances (TBARS), a measure of lipid peroxidation, was higher in nine healthy young men with type 1 diabetes than in control men both at rest and after exercise, suggesting increased oxidative stress. An inverse correlation between resting plasma TBARS and VO2max was found in the diabetic men, which could imply a protective effect of physical fitness against lipid peroxidation. The nine young diabetic men also had lower erythrocyte Cu,Znsuperoxide dismutase and catalase activity, but higher glutathione reductase activity. Coupled with increased plasma TBARS and blood total glutathione levels in the diabetic men, these changes may reflect increased susceptibility to oxidative stress and compensatory adaptations of glutathione homeostasis in response to increased oxidative stress. The WHO and NCEP definitions of the metabolic syndrome appear valid, identifying individuals of a population-based cohort of middle-aged men (n=1005) with a 5-9 -fold increased likelihood of developing diabetes during follow up. The modified WHO definition based on waist-hip ratio >0.9 was the most sensitive in detecting prevalent and incident diabetes and had good specificity. The NCEP definition of the metabolic syndrome with adiposity defined as waist girth >102 cm was the most specific, but did not detect most cases of incident diabetes. In a subset of men without diabetes or the metabolic syndrome at baseline, those who engaged in more LTPA, especially vigorous, or who were more fit were less likely to develop the metabolic syndrome during the four-year follow up. These findings support promotion of moderate and vigorous leisure-time physical activity in otherwise healthy type 1 diabetic men to improve dyslipidemia and cardiorespiratory fitness and possibly decrease lipid peroxidation, and in middle-aged non-diabetic men, to decrease the risk for development of the metabolic syndrome and thereby chronic and progressive diseases such as diabetes and atherosclerosis.