Vol. 4 No. 2: Summer Solstice, 2002
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Exercise and Blood Sugar Management In Type 1 Diabetes

Dr. Eric G. Norman PhD
Staff Member with the Division of Endocrinology University of British Columbia, Vancouver, B.C.

The general rules for blood sugar management in conjunction with exercise will vary depending on whether you are a type 1 diabetic or a type 2 diabetic. With that in mind this article, the first in a series of two articles, will discuss what is known about the basics of energy metabolism in our bodies, whether at rest or exercising and will consider the benefits and the risks associated with exercise for type 1 diabetics. Finally we'll consider different approaches for managing blood sugars before, during and after exercise. Ultimately the goal is to allow the type 1 diabetic to exercise safely by understanding what is going on in their body and still achieve reasonable blood sugar readings before, during and after exercise. Next issue we will discuss exercise as it pertains to type 2 diabetes.

A Brief History

Did you ever wonder how type 1 diabetes was managed prior to the discovery of insulin? It turns out that diet and exercise were the main therapies although exercise was difficult because of the associated metabolic abnormalities. Once insulin therapy became available it was easier for type 1 diabetics to exercise but still blood sugar management was challenging since 1. acute or delayed hypoglycemia was common and 2. post-exercise hyperglycemia and ketosis could also occur. Keep in mind this was all prior to the home blood glucose (BG) monitoring devices that we take for granted today. Back then healthy active individuals with type 1 diabetes were often not permitted to participate in various sports because of the concerns regarding unknown blood glucose levels in conjunction with intermittent activities of varying intensity and duration. With the advent of simple portable BG monitoring and increased understanding of neural and endocrine factors regulating metabolism during exercise it is much safer but still challenging for individuals with type 1 diabetes to exercise.

At present many people with type 1 diabetes are achieving the same level of conditioning and success as non-diabetics, many becoming world class athletes. However, in the general population, type 1 diabetics are on average less fit and have lower aerobic capacity than their non-diabetic peers. Research to date suggests that type 1 diabetics respond normally to physical training and thus the primary obstacle is likely the manner in which type 1 diabetics are educated/encouraged with respect to the benefits and the safety of exercising. There are of course risks as well which need to be considered. When the risks and benefits are weighed, and these will vary for everyone, it is essential to keep in mind the reasons for exercising. They should be for the fun and the fitness primarily. In terms of blood sugar management for the type 1 diabetic, the research to date does not show a significant benefit of exercise and it can actually make blood glucose management poorer and certainly more challenging.

Benefits Of Exercise

Regular exercise has many benefits to health and these are listed in Table 1. These benefits hold true for everyone, not just type 1 diabetics. Most of these are self-explanatory but a few points are worth adding. Since people with diabetes are at higher risk for premature cardiovascular disease, retinopathy, neuropathy and nephropathy it may be particularly worthwhile to pursue some form of physical activity as a part of day to day living. There are also the psychological benefits including a better quality of life and improved self-esteem. This is especially important for someone who is faced with the challenges and restrictions of living with a chronic disease.

Table 1. Benefits of exercise for patients with Type 1 Diabetes
  • Lower blood glucose concentration during and after exercise
  • Improved insulin sensitivity and decreased insulin requirement
  • 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.

Although exercise does lower blood sugars, at least temporarily, overall blood glucose control may not be improved. Some studies have failed to show any benefits while others have shown modest benefits. Post-exercise hyperglycemia as well as additional caloric intake during or following exercise could be two reasons why benefits may not appear. Those are the averages however and individuals who are meticulous about food intake, BG monitoring, and insulin adjustments before, during and after exercise may be able to improve their overall BG management. However for the majority of individuals Edward Horton said it very nicely:

"... an exercise program should not be prescribed for individuals with type 1 diabetes mellitus for the sole purpose and expectation of improving long-term glycemic control. Individual preferences and the desire to participate in recreational exercise or sports, as well as the more general health benefits of exercise, should be the primary considerations in initiating an exercise program for a person with type 1 DM."1

Risks of Exercise

There are several risks associated with exercise as noted in Table 2. These have to be weighed against the benefits when deciding on whether an exercise program is appropriate and if so what type of program. Especially in adults and in particular when long-term complications of diabetes have begun to appear it is essential that these are properly assessed and appropriate precautions taken when planning an exercise program. Review the list in Table 2 and determine which warnings may apply to you. Ask your own doctor or diabetes specialist if you have any uncertainties about your status with respect to these risks. Although the list is long do not let that discourage you from initiating some type of an exercise program, however modest it may be.

Table 2. Risks of exercise for patients with Type 1 Diabetes
  • Hypoglycemia
    • Exercise-induced hypoglycemia
    • Late-onset post exercise hypoglycemia
  • Hyperglycemia after very strenuous exercise
  • Hyperglycemia and ketosis in insulin deficient patients
  • Precipitation or exacerbation of cardiovascular disease
    • Angina pectoris
    • Myocardial infarction
    • Arrhythmias
    • Sudden death
  • Worsening of long-term complications of diabetes
    • Proliferative retinopathy
      • Vitreous hemorrhage
      • Retinal detachment
    • Nephropathy
      • Increased proteinuria
    • 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

Vol. 4 No. 2: Summer Solstice, 2002
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