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June 27, 2000

Exercise and Sports, Hypoglycemia

Question from Downingtown, Pennsylvania, USA:

I am a 55 year old male with a 12 year history of Type 2 diabetes (or maybe not). I started seeing a specialist 4 months ago who placed me in intensive insulin management using Humalog. I engage in intense exercise for 45 minutes every week day and 1-1/2 to 2-1/2 hours every weekend day year-round using an uphill assault vehicle (mountain bike). For the years that I am able to, I intend to increase my level of aggressiveness and fitness in the hope that in my decline I will be able to continue to participate in the sport at some level. I experience a lot of lows, the only downside to which, I understand, is increasingly reduced sensitivity to same. Is there anything besides not having lows that will slow or minimize reduction in sensitivity to lows? At what point does this reduction in sensitivity translate to not being able to function; i.e., work, drive, walk, etc.?


Your question brings up an excellent point that those of us with diabetes do not like to think about. But there are unfortunately many more downsides to low blood sugar than just the loss of symptoms to which you refer. To my knowledge, the only way to improve your awareness of low blood sugar is to maintain your target blood sugars slightly higher for a time, as well as avoiding the lows. Living with diabetes myself, I have to admit that I too have a tendency to become complacent about lows. However, I will also say that hypoglycemia can be dangerous — possibly resulting in seizure, progressive dementia, and even death.

Having said that, avoiding hypoglycemia should be as much a priority for people with diabetes as managing high blood sugars. And while the frequency of low blood sugar certainly increases around exercise, understanding your own personal response to exercise and making appropriate adjustments in insulin dosage, carbohydrate intake, or both will minimize the frequency and severity of lows.

Intensive insulin management should ideally result in more flexibility and control. You don’t say what time of day you generally exercise, but typically it is recommended that the Humalog dosage at the meal just prior to exercise be reduced between 40-60%. In addition, you may need to use a pre-exercise snack to avoid the lows. Talk to your healthcare team about how this can work for you. You may also need to adjust your long-acting insulin dosages downward on your exercise days as well. Glucose monitoring surrounding exercise (before, during and after) will tell you how well this approach works for you, and guide you in making adjustments. Use monitoring to determine your “typical” blood sugar decrease from exercise. It would not be uncommon, with 45 minutes of intense exercise, to experience a drop in blood sugar of 60 – 120+ points. That would require at least 30 grams of carb to balance out. A blanket recommendation is at least 15 grams of carbohydrate for every 30 minutes of exercise, and you may need more than that depending on your level of intensity, your pre-exercise blood sugar, and time of day you are exercising as it relates to your insulin peaks. Regardless, you should always carry a quick-acting source of carbohydrate with you while exercising.

Maintaining good blood sugar control surrounding exercise will assist your performance, and help you to continue enjoying that “uphill assault vehicle” for many years to come!