When a patient with diabetes is also an athlete, there are myriad concerns, preparations, and precautions for patient and doctor alike.
Emily Westfall does her “long runs” on the weekends, 10 to 12 miles to train for a half marathon. She likes to run these miles mid-morning, so the temperature is just right, not too cold, not too hot. She wakes up at 8:00 to hit the pavement by 10:00.
But in those two hours pre-run, Westfall has to prepare for the two-hour run ahead. Westfall has type 1 diabetes (T1D), which means there’s a lot to do before, during, and after the run. “If it’s a 10-mile run,” she says, “I’d assume I’d do that in an hour and a half to two hours, so I’ll probably do a two-hour [basal] reduction at eight o’clock, two hours before my run.”
Westfall reduces her basal to 70% between 8:00 and 10:00, then resumes the basal to normal right before she starts running. She keeps her pump on during the run and carries a Camelbak hydration pack stocked with glucose tabs, granola bars, and “running goo.” She brings her test kit and some type of liquid, usually straight water or some kind of carbohydrate/electrolyte mixture.
During the run, Westfall tests her blood sugar. “I trained myself to test while running,” she says. If she needs to treat, she’ll “pull over” and do what needs to be done. “I try to pretend like it’s a race,” Westfall says, “so I try not to stop to test or do any other treatment stuff. What I would do in a race is try to jog it through. I don’t know if that’s necessarily ‘kosher,’ but that’s how I do it.”
After the run, Westfall does another temporary basal reduction for an hour, but she also has to bolus. “I normally spike right after coming back from a run,” she says. “I’ll do a small one-and-a-half unit bolus, and I’ll test my blood sugar more often over the next three or four hours.”
Westfall has an intimate knowledge of the complicated dance of exercise and diabetes beyond her own personal experience. She’s a research assistant at the Barbara Davis Center for Childhood Diabetes at the University of Colorado, Aurora, so she’s able to see the spectrum. “There are people who make it a bigger deal, there are people who make a big enough deal to be safe, and then there are people who don’t even think about it,” she says. “We have kids in the clinic who say, ‘Well, I’m on the track team,’ and they have the same thought that I had: I have diabetes and if I go low, I’ll drink juice. But you have to balance out that high aspect too, because if your blood sugar is high, you’re not going to be able to exercise at the optimal level.”
Research has also shown that it can be tricky to manage diabetes with exercise. Th at’s not to say diabetic patients shouldn’t exercise; far from it. Exercise increases insulin sensitivity and lowers blood sugar levels, which are obvious benefi ts to these patients, but things get dicey when blood glucose levels drop too much during or after exercise, as the body increases its utilization of glucose for fuel.
Paul Wadwa, MD, also of the Barbara Davis Center for Childhood Diabetes at the University of Colorado, said during his presentation at ENDO 2013 in San Francisco that the challenges are mostly in T1D patients, “when it comes to exercise and insulin adjustments.” Diabetic patients, especially those with T1D, must then know how their physical activities aff ect them and make real-time adjustments with their medications and food intake, as exercise increases the risk of hypoglycemia. A number of studies have also taken other factors into consideration, shedding new light on ways for controlling diabetes symptoms while staying fit.
“Challenges exist for patients with diabetes who are at risk for hypoglycemia when they exercise,” Wadwa says. “I am most concerned about patients on insulin. This includes all patients with T1D and a much smaller percentage of T2D patients. Patients on oral medications with the risk for hypoglycemia (such as those taking sulfonylureas) would also be at risk, but the adjustment in oral medication around exercise should be less challenging than the adjustments in insulin doses.”
Thomas P. J. Solomon, PhD, of the University of Copenhagen, Denmark, and his team wanted to understand the so-called “intersubject variability” in glycemic control following exercise as a way of individualizing treatment for diabetic athletes and published their fi ndings in the Journal of Clinical Endocrinology & Metabolism (JCEM). In this study, the researchers found that around 90% of subjects had an increase in insulin sensitivity following exercise but only around two-thirds of subjects had a reduction in blood glucose levels, as measured by either HbA1c, fasting glucose, or the two-hour glucose during an oral glucose tolerance test (OGTT). They did not find a relationship between the training-induced change in insulin sensitivity and the training-induced change in glucose levels.
However, the scientists did find that the training-induced change in the insulin secretory response to oral glucose ingestion (a marker of beta-cell function) was reflected by the traininginduced change in glucose levels.
Solomon and his team concluded that intersubject variability in restoring glycemic control following physical activity is explained by changes in insulin secretion. “Thus,” they wrote, “baseline and training-induced changes in beta-cell function may be a key determinant of training-induced improvements in glycemic control.”
Solomon also notes that future work should conduct a large-scale randomized controlled trial using more sophisticated techniques for measuring beta-cell function. “Furthermore,” he adds, “it would be prudent to stratify participants based on pre-intervention beta-cell function. In this way, solid conclusions regarding the potential role of pancreatic beta-cell function in the adaptations to exercise training could be made.”
So those are things patients can’t necessarily control, but there are factors that they can do something about. Time of day and intensity of exercise can play a role in how well glucose levels are maintained.
Researchers in Australia found that the risk of “exercise-mediated hypoglycemia” increases during exercise and for several hours after moderate-intensity physical activity and published their fi ndings in JCEM. Raymond J. Davey, PhD, of the Telethon Kids Institute, Perth, Australia, and his colleagues had already reported a biphasic increase in glucose requirements to maintain euglycemia after late-afternoon exercise, “suggesting a unique pattern of delayed risk for nocturnal hypoglycemia.” So they set out to determine whether the same pattern of glucose requirements occurred if patients exercised earlier in the day.
Th e researchers measured the amount of glucose infused to maintain stable blood glucose levels as a surrogate for hypoglycemia risk. Th ey showed that that glucose requirements are increased during and for 11 hours post-exercise in adolescents with T1D, suggesting an increased risk of hypoglycemia over this period.
“We suggest that this increase in glucose requirements is due primarily to an increase in peripheral glucose uptake,” Davey says. “Previously, we showed a diff erent pattern of glucose requirements when exercise was performed in the late afternoon rather than at 12:00 pm. Th is suggests that the time of day when exercise is performed is an important determinant of hypoglycemia risk in adolescents with T1D.”
But again, Davey warns against generalizing. “It is important to mention that we assessed the risk of hypoglycemia following moderate-intensity exercise under the conditions described,” he says. “There are many studies that show that this risk is aff ected by numerous other factors including the intensity and duration of exercise, circulating insulin levels, and the availability of both supplemental and stored carbohydrates.”
The Starting Line
Th ere’s a lot of planning that goes into tailoring an exercise plan for diabetic, athletic patients, and most experts agree that more research needs to be conducted before settling on a perfect plan. Th ere are just too many variables, so athletes usually have to go the trial-and-error route.
“Th e interesting thing is that it’s not just an individually personal thing,” Westfall says. “It’s an individual workout basis. I can say 90% of the time it works to reduce my basal rate an hour before my run, for the amount of my run.” But there are variables that throw Westfall’s planning off , like when it’s very hot out or when she’s eaten foods she doesn’t normally eat. “Every time you go to do a workout,” she says, “you have to think: ‘What’s the temperature out? What am I wearing? How much insulin do I have on board? What’s my basal rate? Am I running low? Have I had a low in the last 12 hours? Have I been running high all day? Th ere are probably 17 to 20 diff erent things you have to think about before you can go out and eff ectively exercise or train.
“Th e thing I think a lot of patients don’t want to hear [ from their endocrinologist] is ‘You’re going to have to fi gure it out for yourself,” she says. “And while that’s ultimately true, we’d like to have some suggestions, a starting point.” Davey says that current guidelines for the prevention of hypoglycemia with exercise in T1D off er generalized recommendations combined with a trial-and-error approach. “Th ese recommendations provide a starting point, but there are several limitations,” he says, “such as limited information on insulin and carbohydrate adjustments in response to diff erent types and intensities of exercise. As a result, current advice is to develop personalized plans using the guidelines as a starting point.”
Solomon agrees, but with a couple of caveats. “Individualized approaches for maximizing athletic performance have been used for decades,” he says. “However, in healthcare, the recommendations for exercise are a ‘one size fits all’ approach. Given the data from our own group and that from studies such as the HERITAGE trial, showing the large variability in the health outcomes following training, an individualized approach for using exercise as medicine seems very sensible. However, there is no current evidence that can allow us to predict what type of exercise plan will lead to the biggest health gain for a specific individual.”
Solomon recommends the American Diabetes Association’s “excellent” baseline plan for adults with diabetes: more than 150 minutes per week of moderateintensity aerobic exercise (50%-70% of maximum heart rate) combined with resistance training on at least two days a week with no more than two consecutive days without exercise.
Wadwa advises patients to over-prepare by keeping glucose and snacks on hand at all times during physical activity, and logging everything — blood sugar, food intake, what time of day the patient exercises. He also suggests that the patient train with someone who could help if he or she “runs into trouble.”
Westfall has found that the over-preparing approach works best for her. “What really helps me have successful training sessions and races is making sure I check off all that stuff on that list and have a plan,” she says. “I’d say it’s 60% preparation and 40% execution to make sure you balanced your ‘good’ blood sugars during your exercise.”
Research in this particular fi eld is ongoing, a kind of marathon itself, and the future looks bright. Solomon points to drug therapies as an interesting development. “What is particularly exciting right now are the advances being made with regards to the potential interaction between exercise and drugs commonly used to treat diabetes (e.g., metformin, rosiglitazone, statins), and the epigenetic adaptations to exercise (DNA methylation, microRNA expression).”
For now, the experts say that finding an activity that the patient enjoys is the first step toward maintaining an exercise schedule. “The health benefi ts of a physically active lifestyle are well established and particularly important for people with T1D,” Davey says. “Therefore, I’d suggest that the best approach is to find an exercise type or program that provides the greatest enjoyment to increase the likelihood of adhering to regular exercise.”
“I advise our pediatric patients to find exercise that they enjoy,” Wadwa says. “If they are miserable when they go to the gym, they are not going to want to go.”
Solomon agrees, commenting on obese patients who may lack motivation to engage in physical activity, which can often be a challenge. “Based on anecdotal observations from our own research experiences, enjoyment is key,” he says. “So to an obese individual with T2D who wanted to start exercising, I would suggest fi nding an environment in which they feel comfortable, an exercise mode which they fi nd fun, and a social group with whom to interact and exercise with.”
— Bagley is the associate editor of Endocrine News. He wrote about online review sites in the October issue.