Often our patients with diabetes have unexplained hypoglycemia and there seems to be no rhyme or reason as to why. Sheri Colberg, Ph.D., FACSM has the latest research on what happens to cause this. Read Exercise and Hypoglycemia: Their Effect on Hormonal Responses
Exercise and Hypoglycemia: Their Effect on Hormonal Responses
By Sheri Colberg, Ph.D., FACSM
Just in the last 5 years or so some new research has finally looked at the physiology behind why low blood sugars can sneak up on you at some times more than at others. Not surprising to most athletes, exercise can have a lot to do with it. Unfortunately, if you’ve had diabetes for longer than 10 years, you likely have a blunted release of glucose-raising hormones (e.g., glucagon and adrenaline) in response to hypoglycemia, meaning that your body will release less of these hormones than it used to and your blood sugars may stay or go lower than before.
Before Hypoglycemia Increases Hypo Risk During Exercise
Having an episode of hypoglycemia may blunt your body’s hormonal response the next time you do any exercise within a day or so. For instance, in one study, volunteers with type 1 diabetes underwent two 2-hour periods of hypoglycemia (experimentally induced) with glucose levels clamped at about 50 milligrams per deciliter (mg/dl), or 2.8 millimolar (mmol/L). The next day, they did 90 minutes of cycling exercise and experienced an extremely blunted release of glucose-raising hormones, which shows that having a bad low the day before may make it harder for your body to keep your glucose levels up when you exercise the next day. What’s more, women’s hormonal responses appear to be better preserved during exercise the day after a low compared with men’s, making the fairer sex better able to respond to exercise-induced lows. Similarly, having a prior bad low blood sugar reaction makes your hormones less able to respond to the next low when it comes along.
Finally, how low you go also appears to make a difference in your ability to respond the next time. In another recent study, different levels of hypoglycemia were induced: 70 (3.9), 60 (3.3), and 50 mg/dl (2.8 mmol/L). After undergoing two 2-hour periods at one of these levels versus a more normal blood glucose level, volunteers did 90 minutes of moderate-intensity cycling exercise the next day. When their glucose levels had remained normal the previous day, they had perfect hormonal responses to exercise, but any hypoglycemia, even just down to 70 mg/dl (3.9 mmol/L), blunted their hormonal responses. In fact, the lower they had been kept the previous day, the worse their responses were during their next-day workouts. These results give you just one more reason to try to prevent lows, especially bad ones, if you want to keep from having low blood sugars during your next exercise session.
Prior Exercise Decreases Hormonal Responses to the Next Low
Along a similar vein, two 90-minute bouts of either low- or moderate-intensity cycling blunt the release of key glucose-raising hormones in response to next-day hypoglycemia, which means that you’re more likely to develop bad lows the day after you exercise. This exercise-induced effect appears to occur rapidly—within a couple of hours—and can increase your risk of getting low for the rest of the day after you worked out and the following one.
This column is excerpted from Diabetic Athlete’s Handbook (released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for type 1 and type 2 diabetic exercisers. Look for it in stores or find links to places to buy it online on www.shericolberg.com, along with additional information.