increase further their physical activity as much as possible and record the type ... increased physical activity and loss of abdominal fat and a decrease in blood ...
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Impact of Physical Activity on Cardiovascular Risk Factors in ID DM ROGER LEHMANN, MD VLADIMIR KAPLAN, MD ROLAND BINGISSER, MD
KONRAD E. BLOCH, MD
GlATGEN A . SP1NAS, MD
OBJECTIVE — To study the impact of physical activity on glycemic control and plasma lipids [HDL cholesterol (HDL-C), HDL-C subtractions, 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. RESEARCH DESIGN A N D METHODS— Well-controlled subjects with IDDM (n = 20; HbAlc = 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. RESULTS— 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/1; 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 < 0.001), 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. CONCLUSIONS — 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 lipidrelated cardiovascular risk factors, with a preferential increase in the HDL3-C subfraction.
T
he prevalence of coronary heart disease (CHD) increases severalfold in diabetic patients (1-3). However, most of those studies have been performed in NIDDM subjects, or the type of diabetes has not been classified. In IDDM patients, the prevalence of CHD is between 4 and
21% (4,5). Epidemiological evidence shows that lipids and lipoproteins are normal in IDDM if good glycemic control is maintained and the patient does not have microalbuminuria or clinical nephropathy. The prevalence of dyslipidemic episodes in IDDM is difficult to evaluate since inade-
From the Division of Endocrinology and Diabetes (R.L., G.A.S.) and the Division of Pneumology (VK., R.B., K.E.B.), Department of Internal Medicine, University Hospital Zurich, Zurich, Switzerland. Address correspondence and reprint requests to Roger Lehmann, MD, Division of Endocrinology and Diabetes, University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland. E-mail: rogerlehmann® compuserve.com. Received for publication 7 February 1997 and accepted in revised form 17 June 1997. Abbreviations: AER, albumin excretion rate; B1A, bioelectrical impedance analysis; BP, blood pressure; CHD, coronary heart disease; HDL-C, HDL cholesterol; LBM, lean body mass; Lp(a), lipoprotein(a); SSPG, steady-state plasma glucose; SSPI, steady-state plasma insulin; TG, triglycerides.
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quate treatment o* IDDM patients increases hepatic VLDL production and decreases lipoprotein lipase activity (6). Multiple compositional changes in lipoproteins may occur even with adequate glycemic control. These dyslipidemic changes are probably important contributors for accelerated atherosclerosis in these patients. Exercise should be encouraged in people with IDDM for the same reason it is encouraged in the general population (7). However, in patients with IDDM the beneficial effects of regular exercise are less clear than in patients with NIDDM. Since inactivity is a major cause of glucose intolerance and insulin resistance (8), physical activity may have a beneficial effect on several cardiovascular risk factors. In a recent study (5), decreased physical activity was associated with CHD in male IDDM patients. Chazan et al. (9) showed that >90% of diabetic patients who survived up to 45 years without any major complication were involved in regular physical activity. Already, adolescents with IDDM may have an increased cardiovascular risk profile with higher systolic and diastolic blood pressure and a higher heart rate (10). The aim of the present study was I) to assess the impact of increased physical activity on insulin sensitivity, glycemic control, plasma lipids [HDL cholesterol (HDLC), HDL-C subfractions, triglycerides, lipoprotein(a)], blood pressure, weight, and body composition, 2) to determine the risks (particularly hypoglycemic episodes) of physical exercise, and 3) to quantify the necessary adaptations in diabetes management in IDDM patients. RESEARCH DESIGN A N D M E T H O D S — Twenty patients with IDDM from the Diabetes Unit of the University Hospital Zurich, age 22-48 years (mean ± SD, 33.0 ± 7.7; 7 women, 13 men), agreed to participate in a 3-month supervised exercise training program. Informed consent was obtained, and the study was approved by the medical ethics committee. The patients were well controlled on multiple insulin injection therapy, employing the basal-bolus system and blood glucose self-control (n > 4 per day) and diet (Table 1). Exclusion criteria were
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Table 1—Baseline characteristics of IDDM patients
Anthropometric and demographic data n Mean age (years) Sex (M/F) Duration of diabetes (years) Mean BM1 (kg/m2) Mean body weight (kg) % body fat Waist-to-hip ratio History Hypertension requiring treatment Nonproliferative diabetic retinopathy Peripheral neuropathy Microalbuminuria (>20 ug/min) Smokers Weekly alcohol intake (g) Severe hypoglycemic episodes per patient-year Mean weekly physical activity (range) (min) Median weekly physical activity (25th, 75th percentile) Therapy Total daily energy intake (kcal) Total insulin requirement (U/kg per day) Glycemic control Mean HbAlc (%) (normal: 4.0-6.4%)
20 33 (22-48) 13/7 11.0 ±7.0 23.0 ±1.7 70.7 ± 10.9 21.9 ±8.2 0.88 ±0.055 0 3 2 2 2 35 (0-210) 0.14 195 (30-720) 150 (60, 275) 2,220 ±525 0.68 ±0.21 7.6 ±1.0
Data are n (range) or means ± SD.
symptomatic CHD, autonomic neuropathy, and the inability to increase the amount of physical activity (e.g., high workload, social engagements, etc.). All patients completed the study and attended our outpatient clinic for more than 6 months (mean 23.8 ± 10.6 months) before the study. They had been instructed repetitively on the benefit of physical activity, regular blood glucose monitoring, and diabetes diet. Patients were in stable diabetes control and did not receive any additional counseling during the study period. Each patient served as his own control. Thus the study effect was limited to increased physical activity. The anthropometric and demographic data at baseline are shown in Table 1. Study design All patients were interviewed during the baseline visit. Information was obtained on hypertension, cigarette smoking, dietary intake, and socioeconomic status, level of physical activity, current medication, and alcohol consumption. Analyses were done after a 12-h overnight fast, 16 h or more after the last bout of exercise for blood glucose, HbAlc, plasma insulin, C-peptide, total cholesterol, 1604
triglycerides (TG), HDL-C, HDL2-C, HDL3C, apolipoproteins A-l and B, lipoprotein(a) [Lp(a)], and albumin excretion rate (AER). Body weight was measured to the nearest 0.1 kg. Height was measured to the nearest centimeter. BMI was calculated as weight (kilograms) divided by height (meters) squared. Waist circumference was measured to the nearest 0.5 centimeter at the level of the umbilicus with the patient standing and breathing normally. Hip circumference was measured to the nearest 0.5 centimeter at the level of the greater trochanters. The average of three readings was taken as the measurement of each circumference. The readings were done by a single observer. Body composition was assessed with bioelectrical impedance analysis (BIA) using the BIA 101/A (Akern, RJL System Detroit, MI), which has been validated before in IDDM patients (11). Blood pressure (BP) was recorded after 5 min in the supine position during the interview with a mercury sphygmomanometer. Pressure was taken to the nearest 2 mmHg, and the average of three measurements during a 15-min period was calculated. Of the patients, 15 of 20 agreed to monitor their BP for 24 h before and
after the intervention period. BP was measured half-hourly during the subjects' estimated waking hours between 0700 and 2200 each day and measured hourly for the remaining (overnight) period using an ambulatory sphygmomanometric device (SpaceLabs, 90207, Redmond, WA). All patients had a prescribed diabetes diet with 50% carbohydrates, 35% fat, and 15% protein content. The actual daily intake was assessed by a diet diary over 5 days at baseline, and at 3 months the intake was 2,220 ± 525 and 2,415 ± 516 kcal per day (P < 0.05), with 42 and 48% carbohydrates (NS), 42 and 39% fat (NS), 16 and 13% protein (NS), respectively. The average weekly alcohol intake was 35 ± 54 and 37 ± 49 g (NS). Each patient participated in a comprehensive teaching program for self-management of diabetes during exercise to prevent exercise-induced hypoglycemic episodes. To apply this theoretical knowledge, all patients took part in a 1-week sport camp with high-intensity activities of 4 to 6 hours' duration (mountain biking, long-distance running, mountain hiking). Blood glucose, carbohydrate intake, and hypoglycemic episodes were recorded with a portable computer logbook (Camit-S, Boehringer Mannheim, Rotkreuz, Switzerland). Protocol of exercise program and fitness evaluation Patients who participated in the exercise program were instructed by one of the investigators and a physical therapist to exercise at least three times per week for 45 min or, if baseline activity exceeded this level, to further increase the amount of physical activity as much as possible. Activities were recorded in a logbook. They included road and mountain biking, jogging, and hiking with heart rate at 50-70% of the Vo2max determined by cycle ergometry. Heart rate was monitored during training periods by heart rate monitors (Polar Target, Stamford, CT). All participants performed bicycle ergometry and a 3-min step test with measurement of heart rate (12) before and after the 3-month study period. Cardiopulmonary exercise testing was performed with an electronically braked bicycle (Bosch, Medicare, Zurich, Switzerland) and a metabolic measurement system (SensorMedics 2900, Yorba Linda, CA). Breath rate, tidal volume, minute ventilation, oxygen uptake, and carbon dioxide output were determined breath by breath. Heart rate was determined with the electrocar-
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Lehmann and Associates
diograph (ECG) (Servomed, Hellige, Freiburg im Breisgau, Germany). Averages of cardiopulmonary variables were calculated over 30-s periods. Maximal values were denned as those associated with the highest attained oxygen uptake. The latter was termed Vo2max and expressed as milliliters per minute. Evaluation of hypoglycemic episodes Hypoglycemia grade I was defined as blood glucose measured in whole blood of
