Vol. 4 No. 4: Winter Solstice, 2002
Exercise and Blood Sugar Management In Type 2 Diabetes
Dr. Eric G. Norman PhD
Staff Member with the Division of Endocrinology University of British Columbia, Vancouver, B.C.
This is the continuation of an article started in the last issue discussing type 2 diabetes and how to manage blood sugars during and after exercise. A number of key ideas regarding the fundamentals of fuel metabolism in conjunction with exercise were discussed in the first article in Fall Equinox, Vol. 4, No. 2. I recommend you review the information since it is relevant to this article.
Type 2 diabetes is typically the result of the following breakdowns in glucose regulation :
- increased insulin resistance in the body tissues
- decreased insulin output by the pancreas
- excessive glucose output by the liver.
Therapies for type 2 diabetes are varied and will change over time as the disease progresses. Insulin resistance, insulin production and excessive liver glucose production all change over time and require adjustments in therapy. As discussed in the last issue the nature of the diabetes therapy will determine the degree of risk of low blood sugars and the necessary precautions to take before exercising. We will get to that later but first let's elaborate on the benefits and risks associated with exercise.
Benefits Of Exercise
There are numerous benefits of a regular exercise program and they are listed in table 1. I will highlight a few of my favorites here. One of the immediate benefits, besides having fun and feeling good, is the reduction in blood sugar. There is typically an immediate reduction in the blood glucose levels towards normal in response to exercise. The immediate reduction of blood glucose levels with exercise can actually be used to help regulate blood sugars on a daily basis and can lead to long-term improvement in diabetic control. Exercise can also produce a long-term improvement in insulin sensitivity and decreased fasting/after-meal plasma insulin levels when performed on a regular basis (3-5 times a week).
|Table 1. Benefits of exercise for patients with Type 2 Diabetes
- Lower blood glucose concentration during and after exercise
- Lower basal and postprandial insulin concentrations
- Improved insulin sensitivity
- Lower HbA1c levels
- Improved lipid profile
- Decreased triglycerides
- Slightly decreased low-density lipoprotein (LDL) (bad fat)
- Increased high-density lipoprotein (HDL) (good fat)
- Improvement in mild to moderate hypertension
- Increased energy expenditure
- Adjunct to diet for weight reduction
- Increased fat loss
- Preservation of lean body mass
- Cardiovascular conditioning
- Increased strength and flexibility
- Improved sense of well-being and enhanced quality of life
Another benefit is the potential for improved cardiovascular fitness, decreasing the risk for heart disease and increasing energy levels and stamina. In turn these can result in an enhanced sense of well-being and an improved quality of life. Exercise can also result in an improved lipid profile (cholesterol) with research showing lower levels of bad cholesterol (LDL and triglycerides) and higher levels of the good cholesterol (HDL) with a minimum of 10-12 miles per week of moderate intensity jogging. Often there is a reduction of hypertension (high blood pressure). This can occur independent of weight loss or changes in body composition, although these typically occur as well. One of the greatest benefits, however, is the potential to reverse the underlying mechanism of insulin resistance that can lead to diabetes in the first place. Exercise tends to reduce this resistance and increase insulin sensitivity enabling the body to regulate blood glucose (BG) levels more effectively with less insulin. This can be important in the prevention or the delay of onset of type 2 diabetes as well as the treatment.
It was back in the 1970's that researchers first proposed exercise as a way to treat insulin resistance associated with type 2 diabetes. What they found was that physically active people with diabetes had lower fasting levels of insulin as well as lower insulin levels following a glucose challenge when compared to untrained diabetics of the same age and weight. The exercise resulted in increased sensitivity to insulin and therefore the pancreas didn't need to produce as much insulin to achieve a similar glucose level. Exercise has been shown to increase insulin-stimulated glucose disposal by 30-35% and this correlates with increased aerobic capacity and is known to be a result of increased uptake of glucose by skeletal muscle and not as a result of reduced liver output of glucose. Glucose disposal refers to the removal of glucose from the circulating blood and into body tissues.
The beneficial effects of insulin sensitivity associated with exercise are lost when exercise is discontinued. The time frame is not entirely clear. There is some evidence indicating that much of the effect is lost after 60 hours while other studies indicate it can last as long as 5 to 7 days. It has even been shown that a single bout of exercise in untrained individuals can increase insulin sensitivity for 2-5 days. So although the effect doesn't last forever it does last for a while and this can reduce the total insulin requirements and improve overall blood sugar management. The mechanism is not entirely understood but is believed that it may be related to increased capillary density in skeletal muscle, increased oxidative capacity of skeletal muscle and increased skeletal muscle GLUT 4 glucose transporter content. In other words the muscle has more blood vessels, can burn glucose more effectively and has more shuttles to move the glucose out of the blood and into the muscle tissues.
Interestingly enough the research seems to indicate that even though there is improved insulin stimulated glucose uptake as a result of exercise there doesn't appear to be any improvement in fasting blood glucose levels. There is however, a reduction in the HbA1c indicating that overall blood glucose management is improved as a result of regular exercise. For those of you who may not be familiar with the HbA1c it stands for glycosylated hemoglobin and represents an approximation of the 3 month average of the blood glucose levels weighted more heavily on the more recent levels. It is proposed that the improved HbA1c is the result of frequent episodes of lower blood glucose levels associated with exercise and the after effect of prolonged reduced blood sugars which results in a lowering of the average blood sugar.
For those of you who enjoy weight lifting you'll be glad to know that a recent study (3) showed a significant reduction in HbA1c as a result of high-intensity resistance training.
A group of 47 type 2 diabetics, men and women, were randomized to either 1. modest weight loss or 2. modest weight loss in conjunction with high-intensity resistance training. The group was 60-80 years of age and used diet and/or medication to manage their diabetes. They were all overweight, sedentary, were not taking insulin and had a HbA1c between 7-10%. All research participants were placed on a healthy eating plan with the intention of a weight loss of 0.25 kg per week. The exercise group attended the gym 3 non-consecutive days per week. Each session included a 5 minute warm-up and cool-down with 45 minutes of high-intensity resistance working both the upper and lower body. Instructors supervised the workouts to ensure proper technique and to assess the workload.
After 6 months both groups had similar changes in terms of weight loss, reduced waist circumference, reduced energy intake, no change in blood lipids, no change in fasting insulin and glucose.
The benefits seen in the training group were a greater reduction in HbA1c, increased strength, a greater reduction in blood pressure and increased lean body mass. Keep in mind this was the result of a high-intensity workout program and perhaps would have yielded even greater improvements had the training group done some other activity on the days between workouts. This type of workout may not be for all individuals as we will discuss shortly in the Risks section and should only be pursued with the approval of your physician or diabetes specialist.
Risks of Exercise
The risks of exercise are listed in table 2. Yes it is a rather large list and for that reason it is highly recommended that you consult your physician and/or diabetes specialist before starting an exercise program. You can even present them with this list if you wish to be sure they are aware and they can tell which risks apply to you. Exercise can increase the risk of having a low blood sugar either during or after the activity. We will discuss this in much greater detail shortly. It is important to mention that individuals with proliferative retinopathy (eye damage) should be cautious with respect to certain exercises which may cause retinal or vitreous hemorrhage. Exercise with the head lower than the rest of the body (eg. sit-ups, certain yoga moves etc) should be avoided as should extremely strenuous exercise or exercise that raises the blood pressure beyond levels recommended by your doctor. Also exercise that results in rapid or jarring head movements should be avoided because of increased risk of hemorrhage or retinal detachment.
|Table 2. Risks of exercise for patients with Type 2 Diabetes
- Hypoglycemia if treated with insulin or insulin secretegogues (eg. glyburide, amaryl, gluconorm)
- Exercise-induced hypoglycemia
- Late-onset post exercise hypoglycemia
- Hyperglycemia after very strenuous exercise
- Precipitation or exacerbation of cardiovascular disease
- Angina pectoris
- Myocardial infarction
- Sudden death
- Worsening of long-term complications of diabetes
- Proliferative retinopathy
- Vitreous hemorrhage
- Retinal detachment
- Peripheral neuropathy
- Soft tissue and joint injuries
- Autonomic neuropathy
- Decreased cardiovascular response to exercise
- Decreased maximum aerobic capacity
- Impaired response to hydration
- Postural hypertension
- Altered gastrointestinal function