Impact of physical activity on cardiovascular risk factors in IDDM

To study the impact of physical activity on glycemic control and plasma lipids [HDL cholesterol (HDL-C), HDL-C subfractions, triglycerides, lipoprotein(a)], blood pressure, weight, and abdominal fat and to determine the necessary short-term adaptations in diabetes management during intensive endurance training in patients with IDDM.

Well-controlled subjects with IDDM (n = 20; HbA1c = 7.6%) engaged in a regular exercise program over a period of 3 months involving endurance sports such as biking, long-distance running, or hiking. Subjects were instructed to exercise at least 135 min per week. If baseline activity exceeded this level, subjects were to increase further their physical activity as much as possible and record the type and time of such activity.

During the 3-month intervention, physical activity increased from 195 +/- 176 to 356 +/- 164 min (mean +/- SD) per week (P < 0.001). Physical fitness as assessed by VO2max increased from 2,914 +/- 924 to 3,092 +/- 905 ml/min (P < 0.001), and insulin sensitivity increased significantly (steady-state plasma glucose [SSPG] decreased from 10.5 +/- 4.8 to 7.0 +/- 3.3 mmol/l; P < 0.01). Subsequently, LDL cholesterol decreased by 14% (P < 0.05), and HDL and HDL3-C subfraction increased by 10 (P < 0.05) and 16% (P < 0.05), respectively. Systolic and diastolic blood pressure decreased significantly from 127 +/- 9 to 124 +/- 8 (P < 0.05) and from 80 +/- 5 to 77 +/- 5 mmHg (P < 0.01), respectively. Resting heart rate decreased from 63 +/- 6 to 59 +/- 7 bpm (P < 0.01). Waist-to-hip circumference ratio decreased from 0.882 +/- 0.055 to 0.858 +/- 0.053 (P < 0.001), body weight decreased from 70.7 +/- 10.4 to 68.7 +/- 10.2 kg (P = 0.003), with a consequent decrease in body fat from 21.9 +/- 8.2 to 18.0 +/- 6.3% (P < 0.001) and an increase in lean body mass from 54.9 +/- 12.2 to 56.8 +/- 11.0 kg. These effects occurred independently of glycemic control. The overall frequency of severe hypoglycemic episodes was reduced from 0.14 to 0.10 per patient-year during the study period.

This study shows that increasing physical activity is safe and does not result in more hypoglycemic episodes and that there is a linear dose-response between increased physical activity and loss of abdominal fat and a decrease in blood pressure and lipid-related cardiovascular risk factors, with a preferential increase in the HDL3-C subfraction.