Volume 4, Number 3: Fall Equinox, 2002

Exercise and Blood Sugar Management In Type 2 Diabetes - BC Endocrine Research Foundation

Dr. Eric G. Norman PhD

Staff Member with the Division of Endocrinology University of British Columbia, Vancouver, B.C.

This is the second in a two article series on Diabetes and Exercise. This article will discuss 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 the last issue (Fall Equinox, Vol. 4, No.2 ) and I recommend you review that 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.

Typically these breakdowns occur gradually over the course of years. It is worth noting that this is different from type 1 diabetes where the primary problem is the almost complete absence of insulin production by the pancreas with the breakdown being immediately apparent as symptoms can be life threatening. The treatment for type 1 diabetes is relatively simple and the choices few; insulin. In some way some type of insulin will be delivered into the body as treatment. It may be a pen, a syringe, a pump or eventually inhaled but the same principal applies; the provision of insulin that the body’s pancreas no longer makes. With type 2 diabetes the options are varied and will likely change over time as the disease progresses. Insulin resistance, insulin production and excessive liver glucose production will all change over time and require adjustments in therapy. I emphasize this point since, as you will read later, the nature of the diabetes therapy will determine the degree of risk of low blood sugars and the necessary precautions to take before exercising.

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. In addition there is the potential for improved cardiovascular fitness. I think 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.

 

Table 1. Benefits of exercise for patients with Type 2 Diabetes

  1. Lower blood glucose concentration during and after exercise
  2. Lower basal and postprandial insulin concentrations
  3. Improved insulin sensitivity
  4. Lower HbA1c levels
  5. Improved lipid profile
    1. Decreased triglycerides
    2. Slightly decreased low-density lipoprotein (LDL) (bad fat)
    3. Increased high-density lipoprotein (HDL) (good fat)
  6. Improvement in mild to moderate hypertension
  7. Increased energy expenditure
    1. Adjunct to diet for weight reduction
    2. Increased fat loss
    3. Preservation of lean body mass
  8. Cardiovascular conditioning
  9. Increased strength and flexibility
  10. Improved sense of well-being and enhanced quality of life

 

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 can tell which risks apply to you. The most immediate risk for the majority of individuals will be hypoglycemia (low blood sugars), either during or after exercising. To better understand this risk we need to understand the approaches to type 2 diabetes therapy.

 

Table 2. Risks of exercise for patients with Type 2 Diabetes

  1. Hypoglycemia if treated with insulin or insulin secretegogues (eg. glyburide, amaryl, gluconorm)
    1. Exercise-induced hypoglycemia
    2. Late-onset post exercise hypoglycemia
  2. Hyperglycemia after very strenuous exercise
  3. Precipitation or exacerbation of cardiovascular disease
    1. Angina pectoris
    2. Myocardial infarction
    3. Arrhythmias
    4. Sudden death
  4. Worsening of long-term complications of diabetes
    1. Proliferative retinopathy
      • Vitreous hemorrhage
      • Retinal detachment
    2. Nephropathy
      • Increased proteinuria
    3. Peripheral neuropathy
      • Soft tissue and joint injuries
    4. Autonomic neuropathy
      • Decreased cardiovascular response to exercise
      • Decreased maximum aerobic capacity
      • Impaired response to hydration
      • Postural hypertension
      • Altered gastrointestinal function

 

Type 2 Diabetes Therapy

Let’s categorize type 2 diabetes therapies since these have a bearing on the potential for low blood sugars and therefore exercise and safety considerations. I will present them in order of increasing risk of low blood sugars.

  1. This first category representing the lowest risk will include individuals taking any of the following:
    1. No Diabetes Medications
    2. Metformin
    3. Acarbose

    Generally speaking when someone is first diagnosed with type 2 diabetes their physician or diabetes specialist will recommend a period of lifestyle modification (ie. diet and exercise); a minimum 6-8 weeks to see if average blood sugars can be reduced. Historically, prior to the discovery of insulin and the development of oral diabetes medications, this was the only way to treat type 2 diabetes. If lifestyle modification fails it will be recommended that some form of medical therapy be introduced. Typically this will be a drug called metformin that acts by reducing sugar output from the liver to help reduce the average blood glucose (BG) levels, especially morning fasting sugars which are often high as a result of an overactive liver. A second drug Acarbose may also be used, either alone or in conjunction with metformin. This medication acts by reducing glucose absorption from the small intestine thereby reducing the BG rise associated with food intake. In any of the above four circumstances there is virtually no danger of ever having a serious hypoglycemic reaction. In some circumstances the BG levels may go as low as 3.5 mmole/litre but the body would certainly respond by turning up sugar production and reducing insulin production to avoid a further decline in blood sugars.

  2. The natural progression of diabetes is such that BG control may eventually deteriorate over time and another medication is often added, typically an insulin secretagogue. There is a wide range of these currently available but the underlying principal is the same, stimulation of the pancreas to produce more insulin. This second category includes the addition of a secretagogue, typically with metformin but sometimes without and poses an additional challenge in terms of BG management. The challenge is that when taking a secretagogue it is possible that the pancreas may produce too much insulin and result in a severe decline in BG for which the liver cannot compensate. In this scenario BGs may go so low that a coma and possibly death can result.
  3. Eventually there may be further deterioration of BG control and the addition of another medication called an insulin sensitizer (eg. Avandia) which makes the body more sensitive to the insulin it produces. This class of medications is proving to be an excellent therapy for many type 2 diabetics. An insulin sensitizer taken alone poses little risk for a severe hypoglycemic event but if taken in conjunction with an insulin secretagogue, as is often the case, it will increase the possibility of a low BG since the body will now be more responsive to the insulin it produces.
  4. Many people with type 2 diabetes eventually require or may even choose insulin injections to help them manage their blood sugars effectively. I say choose because some individuals would rather inject a hormone that would occur naturally in the body than introduce a variety of drugs that the body’s liver must process. Insulin may be taken with or without oral diabetes medications. When taking insulin subcutaneously the risk of having a low blood sugar is increased. Even more so if insulin is taken with an insulin sensitizer such as Avandia.

These represent four therapy categories and if you have type 2 diabetes you will fit into one of them. Review your diabetes therapy and decide which category applies to you. This is meant to provide a guide for knowing what your relative risk is for hypoglycemia, especially during and after exercising, but also for activities such as driving and day to day living. Knowing what your risk level is helps you to take the necessary precautions for safety and also lets you manage your blood sugars effectively.

In the next issue we will continue this article and discuss the specifics of what you can do to optimize safety and blood sugar control depending on your diabetes therapy.

Eric Norman is a research scientist investigating heart disease in post-menopausal women and in individuals with type 2 diabetes.

References

  1. Exercise in patients with Type 2 Diabetes Mellitus. Horton, E.S.. Chapter 77 in Diabetes Mellitus: A Fundamental and Clinical Text. Second Edition. Editors Derck LeRoith, Simeon I. Taylor, Jerrold M. Olefsky. Lippincott Williams and Wilkins. 2000.
  2. Fuel Metabolism, Exercise and Nutritional Needs in Type 1 Diabetes. Franz, M.J.. In Canadian Journal of Diabetes Care 22:4 pp 59-63.

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