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Exercise in type 1 diabetes must minimize complications, optimize glucose utilization
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The value of regular physical activity as a means for maintaining a healthy weight, boosting mood and controlling cardiovascular risk factors is well-known, and regular exercise is recommended for most individuals to the extent that they are able. For patients with type 1 diabetes, the motivation to exercise includes these factors and more.
“It is well-established that being regularly active can improve overall physical and mental health in people with type 1 diabetes,” Sheri R. Colberg, PhD, FACSM, professor emerita of exercise science at Old Dominion University, in Norfolk, Virginia, told Endocrine Today. “Their goals may be improved fitness, weight loss, overall well-being — the same as individuals without diabetes — but it may also be able to improve insulin sensitivity and diabetes control. With type 1 diabetes, people must balance their insulin doses with their food intake to manage their glucose levels to improve their overall control.”
Managing glucose
According to Richard Peng, MS, ACSM, a clinical exercise physiologist and certified diabetes educator at HealthCare Partners Medical Group in Los Angeles, the main difference in the goal of an exercise regimen between people with type 1 diabetes and those without diabetes is the need to manage and monitor blood glucose.
“I am a big fan of continuous glucose monitoring systems for type 1 diabetes patients, because with CGMs, they are able to check and see what their blood glucose is, even while they’re exercising,” Peng said. “With diabetes, there is dysfunction in glucagon and other functions that people without diabetes don’t have to worry about.”
In patients without diabetes, glucose equilibrium is maintained through a complex process of insulin secretion, suppression of hepatic glucose and stimulation of glucose uptake by the muscles, he said.
“For example, in patients without diabetes, when the body produces lactic acid during exercise, their body automatically converts that to glucose so the muscles can use it as energy,” he said.
Physical activity usually increases insulin sensitivity for 2 to 72 hours after exercise, Colberg said, but exercise can also cause insulin resistance.
“During exercise, circulating insulin promotes uptake of glucose from the blood into active muscles, which can result in hypoglycemia if insulin levels are too high,” she said.“Muscular contractions alone cause blood glucose uptake through a mechanism separate from insulin, and the two effects are additive.”
For this reason, Peng said, people with diabetes need substantially less insulin during exercise than during less active times.
“Usually what happens, particularly with type 1 diabetes and even with type 2 diabetes patients who are on insulin or a sulfonylurea, is the last dose of the insulin or medication prior to exercise is usually significantly reduced,” he said. “For some, it may be reduced by 75% or even more from the original dose.”
An important first step for optimizing exercise in patients with type 1 diabetes is to gain an understanding of their body’s daily fluctuations and responses to exercise, Colberg said.
“Many people with type 1 diabetes avoid exercise due to fear of the hypoglycemia that it may cause,” Colberg said. “It does increase the risk, but it can be avoided. In order to exercise safely and effectively, patients need to understand more about how their insulin works, when it peaks, and how to compensate for activity with food intake and/or insulin dose changes.”
Exercise recommendations
Although the specific exercise regimen, duration and frequency should depend to some extent on the individual patient, Peng makes certain basic recommendations to all patients with type 1 diabetes.
“I recommend that they include a [CV] exercise, a strengthening exercise and a flexibility exercise, and these are all equally important,” Peng said. “Anything specific in terms of goals would depend on their current health condition.”
When advising patients on an exercise regimen, he also considers the patient’s age and level of fitness.
“For example, if it’s a novice exerciser, say, a young female who has never exercised before, I may have her start with 30 minutes of walking every other day,” Peng said. “Whereas a middle-aged male who is in his 40s, who in the past has played basketball several times a week but has gained some weight and wants to lose it, I might start him off with some [CV] exercises, such as walking, cycling or playing basketball every other day, and include some weight training at least twice a week.”
Peng emphasized the value of weight training in a complete exercise program for people with type 1 diabetes.
“What happens is, when you have muscle, your muscles store more glucose as glycogen,” he said. “So, when you exercise regularly and are using those muscles, your bodyhas the capacity to store more glucose in the muscles, your body will utilize glucose more effectively, and the variability in glucose levels is reduced.”
Duration, time of day
Although his usual recommendation for patients with diabetes is 150 minutes of exercise per week, Peng also factors in the patient’s individual circumstances and comorbidities.
“For some patients who have challenges, such as hip pain or other physical issues, the workout would not be the same as for a healthy patient who had only diabetes and no other health problems,” he said.
According to Colberg, exercising at certain times a day, particularly in relation to meals, can help to achieve specific objectives.
“If the goal is to lower blood glucose quickly, exercising within 2 to 3 hours after meals, when insulin is taken, works best, because circulating insulin levels are higher,” she said. “The risk of developing hypoglycemia is heightened then as well, however.”
For patients wishing to prevent hypoglycemia during exercise, working out before meals or at least 3 hours after meals is preferable. Additionally, Colberg said, exercising in the early morning, before insulin, is helpful for preventing hypoglycemia.
“It may also help to do resistance exercise first if blood glucose is on the low side to start, or aerobic first if it is higher,” she said. “People should exercise at whatever time works for them, though, and make insulin and food adjustments to compensate.”
Peng agreed that although he generally does not advise patients to exercise too soon after eating, the main objective is to maintain glucose equilibrium.
“Generally, patients with diabetes should not exercise when blood glucose is low, or when they are hyperglycemic with ketones present, or when they are at the peak of their insulin,” he said, “Patients need to be aware of that information.”
Although patients with diabetes who do not have complications generally do not have restrictions on the types of exercise they can safely do, certain complications may warrant safety precautions.
“For patients with diabetes-related complications, some safety precautions may be necessary, such as avoiding breath-holding in patients with unstable proliferative retinopathy, or monitoring feet daily if they have peripheral neuropathy,” Colberg said. “Beyond this, though, diabetic patients can basically do what everyone else can do.”
Common misconceptions
It is not only patients who may have limited knowledge about how exercise affects diabetes — physicians may also lack this knowledge and, therefore, may not advise their patients to exercise.
“Some providers also overlook the importance of monitoring a patient’s blood glucose when they exercise,” Peng said. “Some physicians may even think that exercise makes it harder for patients to manage their disease. Others may understand the value of exercise, but don’t know what kind of exercise to advise their patients to do.”
These misconceptions seem to be changing, however, Peng said, due in part to increased overall patient interest in healthy lifestyles.
“There are definitely areas where patients and doctors can stand to learn more about this,” he said. “Thankfully, there is a lot more interest now in exercise, and its positive impact in general and on diabetes in particular.” – by Jennifer Byrne
For more information:
Sheri R. Colberg, PhD, FACSM, can be reached at Spong Hall, 5255 Hampton Blvd., Norfolk, VA 23529.
Richard Peng, MS, ACSM-RCEP, CDE, can be reached at 1025 Olympic Blvd., Los Angeles, CA 90404.
Disclosure: Colberg and Peng report no relevant disclosures.