by Sheri Colberg, Ph.D., FACSM
My last article focused on why glucose was the best short-term treatment for hypoglycemia, but this time I want to switch gears and talk about why treating lows is not as straight-forward as you would think. It mainly stems from the fact that sometimes hypoglycemia can be very difficult to treat effectively and even hard to prevent in many cases, particularly related to physical activity.
Take the case of a woman with type 1 diabetes for almost 50 years who emailed me recently. She clearly feels that she is doing something wrong since she used to be able to predict and control her lows when hiking in the mountains multiple days in a row, but now she can’t manage her blood glucose when she does that level of activity.
She wrote, “Years ago you used me as an example of a person who had found the right insulin dose to hike in the eastern Sierras, by going to 50% basal for the uphill part. That’s true, but it is only half the story. I have lows after exercise that occur many hours after, and the effects are cumulative. So, for instance, if I were to hike two days in a row, on the third day, I’d be collapsed ALL DAY and unable to get off the ground, quite literally, due to severe lows. Yes, I can go on 50% basal and get up a hill. But what happens at midnight afterward and in the days after puts me into a lot of what I call ‘down time’ where I am not functional because of lows. This seems to be getting worse as I age. Hiking in the eastern Sierra is actually so dangerous for me I don’t do it anymore, except on the one trail where I know there is cell phone coverage in case someone has to haul me out.”
What is happening to make her management of exercise-related hypoglycemia change? One very likely possibility is that she is suffering from hypoglycemia-associated autonomic failure (HAAF), which can lead to a lesser release of glucose-raising hormones like glucagon and epinephrine in response to lows or exercise. HAAF—and consequently more severe lows—are more likely to occur following a prior bout of exercise in the previous day or two or a prior hypoglycemic event (with longer and lower lows having a bigger impact on responses to the next occurrence). It has even been elicited in people without diabetes who were made hypoglycemic in a lab for two hours at a time twice in 30 hours and subsequently experienced a significant blunting in counterregulatory and symptom response to subsequent hypoglycemia on day 5 (1). In people with type 1 diabetes, even a single episode of hypoglycemia can blunt the body’s normal counterregulatory defenses (neuroendocrine and autonomic nervous system responses) against subsequent hypoglycemia or exercise. Similarly, a single bout of exercise can also blunt counterregulatory responses against subsequent hypoglycemia (2). This is more common in anyone who has had type 1 diabetes for 5 years or longer and in people with type 2 diabetes who make little of their own insulin. So, this woman’s inability to prevent lows after successive days of exercise is likely not her fault at all.
Another partial explanation is that things change in our bodies as we age. It can take longer to recover from bouts of exercise (both in terms of muscle repair and carbohydrate and energy replacement), and her hiking may actually be occurring at a higher relative workload even if she’s hiking at the same pace. Relative exercise intensities increase when people do the same absolute intensity (same hiking speed, distance, etc.) just due to a decline in maximal aerobic capacity with aging. There’s also a gradual loss of muscle mass, which can affect our total storage capacity for muscular glycogen (stored glucose).
What should this woman do? Scrupulous avoidance of hypoglycemia over a period of weeks or a few months may improve hypoglycemia symptom awareness and to a certain extent counterregulatory hormone responses, but it is very hard to accomplish total avoidance of lows without hyperglycemia. Alternatively, although none of us likes to have to curtail our activities as we age, sometimes that is all we really have an option to do. It’s easier to develop overuse and other injuries as we age from doing the same activities we’ve always done, and it will take us longer to recover from doing them. My goal has always been to continue to be active however I can, but even I have found that staying active often requires modifications to exercise regimens and activities.
So, choose what you can do and challenge yourself when appropriate—only when an activity won’t cause injury or severe lows. Certainly challenge your physical and mental limits, but be willing to back off some when necessary to meet your longer term goals. Getting older is certainly not for the faint of heart, but it certainly beats the alternative.
(1) Moheet A, Kumar A, Eberly LE, Kim J, Roberts R, Seaquist ER: Hypoglycemia-associated autonomic failure in healthy humans: comparison of two vs three periods of hypoglycemia on hypoglycemia-induced counterregulatory and symptom response 5 days later. J Clin Endo Metab 2014;99:664-670.
(2) Davis SN, Tate D, Hedrington MS: Mechanisms of hypoglycemia and exercise-associated autonomic dysfunction. Transactions Am Clin Climatol Assoc 2014;125:281-291; discussion 291-282.
In addition to my educational web site, Diabetes Motion (www.diabetesmotion.com), I also recently founded an academy for fitness and other professionals seeking continuing education enabling them to effectively work with people with diabetes and exercise: Diabetes Motion Academy, accessible at www.dmacademy.com. Please visit those sites and my personal one (www.shericolberg.com) for more useful information about being active with diabetes.