Exercise Training in Treatment of Diabetes Mellitus in Elderly Patients

Abstract

There are few data that specifically address the effects of exercise training on elderly patients with diabetes mellitus; thus, much of the information contained herein is extrapolated from studies on young and nondiabetic subjects. With acute exercise, there is a marked enhancement in glucose uptake and utilization despite a decline in plasma insulin concentration. Several hypotheses have been suggested to explain this well-described but seemingly paradoxical situation, and most recently, a muscle-contraction-induced increase in membrane-associated glucose-transporter units has been described. In diabetes, there is a breakdown in the usually precise balance between glucose delivery and utilization necessary to maintain stable blood glucose concentrations during acute exercise. In hypoinsulinemic states (untreated diabetes mellitus), glucose production by the liver can be greater than muscle uptake and utilization, resulting in hyperglycemia. Conversely, in hyperinsulinemic conditions (treatment with large doses of subcutaneous insulin), glucose production can be inordinately suppressed relative to uptake and utilization, resulting in hypoglycemia. Therefore, in diabetic patients, adequate glucose control is important before initiating an exercise program. Endurance exercise training has been suggested as an adjunct to diet therapy for noninsulin-dependent diabetes mellitus (NIDDM) patients. Although early studies showed improvement in insulin resistance (lower insulin levels) with endurance training, little or no benefit in glucose control was demonstrated. More recent studies have noted improvement in fasting plasma glucose and glycosylated hemoglobin concentrations and oral glucose tolerance with endurance training. The difference between these studies may be explained by the time at which the tests were conducted relative to the last episode of exercise, because there appears to be a rapid detraining effect on glucose tolerance after short-term endurance training. Even if the effects on plasma glucose levels are limited, there are other important potential benefits of endurance training in elderly diabetic patients. Maximal and submaximal aerobic capacity both decline with age and are at least partially reversible with endurance training. Potentially even more important are the effects of endurance training on risk factors for atherosclerosis. Endurance training may improve lipid profiles by reducing very-low-density lipoprotein triglyceride and low-density lipoprotein cholesterol while increasing high-density lipoprotein cholesterol. Small reductions in blood pressure are also frequently noted with endurance training. The fall in plasma insulin concentration associated with training may by itself also reduce cardiovascular risk. Obesity is an independent risk factor for cardiovascular disease, and endurance training can be beneficial in producing and maintaining weight loss. This is especially important in the elderly because they are often fatter than their younger counterparts. Recent data suggest that endurance training preferentially reduces central and intraabdominal adiposity in the elderly. This is significant because an increased central distribution of body fat is found in elderly and NIDDM patients. I conclude that, although there is little direct evidence, extrapolated data support a potentially important role for endurance exercise training in the treatment of elderly diabetic patients. The possible benefits are not limited to improvements in insulin and glucose levels but also extend to reduction of important risk factors for atherosclerosis. By following the suggestions contained herein, many elderly diabetic patients can safely benefit from endurance training.