If you’ve been diagnosed with type 2 diabetes, you know that exercise is key for long-term blood sugar control. But it also can affect your blood sugar levels in the short term—and not always in good ways. Exercise too enthusiastically, and you could find your blood sugar level dropping too low—or even spiking.
Here’s how people with type 2 diabetes can handle (and even better, avoid) the two most common exercise/blood sugar problems…
When you exercise, your body gets energy first by using blood sugar (glucose) and then by depleting glycogen, the storage form of glucose, from your muscles and liver. (You may also start burning fat for energy.)
The short-term effect is that blood sugar levels fall—and can stay reduced for as long as 24 hours. That’s the benefit. But if levels fall too low (hypoglycemia)—below 70 mg/dL if your meter measures whole blood, or below 80 mg/dL if it measures plasma glucose—you may feel symptoms, including shakiness, clammy skin, blurred vision and confusion. A severe drop can be scary or even dangerous.
The good news is that it’s rare—and easily prevented. Exercise-induced hypoglycemia is most common in people who take insulin—that is, everyone with type 1 diabetes and some people with type 2. It can also happen if you are taking certain medications that promote insulin secretion, including sulfonylureas and glinides. If low blood sugar during or after exercise happens to you regularly, talk to your doctor about possible solutions such as eating a small snack before (and maybe during) exercise, adjusting your medication dose—or both.
Fortunately, exercise-induced hypoglycemia is quite rare in people who manage their diabetes with lifestyle alone or with a medication such as metformin, which instead of promoting insulin secretion makes your body more sensitive to the insulin it already makes. Still, it’s possible for a mild drop in blood sugar to happen, especially if you train really hard or for more than an hour. Even a mild blood sugar drop might make you feel tired afterward.
The best advice for everyone with diabetes, especially at the beginning of a new exercise program, is to test your blood sugar three times—before, during and after your workout. Once you get a sense of how your exercise routine is affecting your blood sugar, you can cut back on the testing. Just make sure that you have access to a quick energy source such as an energy bar or fruit juice in case your blood sugar drops.
Tip: To reduce your risk for hypoglycemia, do resistance exercise before aerobic exercise.
Sometimes, blood sugar levels get too high—250 mg/dL or 300 mg/dL or even higher—which can cause you to feel symptoms such as thirst, headache, blurred vision and fatigue. It’s called hyperglycemia. It’s an indication that you need to adjust your eating pattern, your medications or both so that you can bring blood sugar to more acceptable levels, such as the mid-100s.
Is it safe to exercise if your blood sugar is already somewhat elevated? The answer is yes as long as you’re feeling good. Exercise can bring high blood sugar levels down quickly. Indeed, with exercise your muscles can burn up glucose at almost 20 times their normal rate. That’s a key reason that regular exercise is so effective in controlling diabetes. Exercising, even a nice brisk walk, is one good way to bring levels down. Make sure you’re staying well-hydrated, too, since high blood sugar can lead to frequent urination and thus dehydration.
Exception: Sometimes, if you start exercising when your blood sugar is already running high, rising adrenalin or other exercise-stimulated hormones can stimulate your body to release even more sugar into the blood—temporarily overwhelming the sugar-burning effect of exercise. If that happens, don’t sweat it. Just cool down as you would any time you exercise aerobically and then sit quietly to allow your body to rest. After 30 minutes, when you test your blood sugar again, you should find that your blood sugar has gone down to more normal levels. In some cases, it might take an hour.
The good news is that for most people with diabetes, exercise won’t cause any short-term blood sugar problems—and it’s one of the best things you can do to control your diabetes.
Check with your doctor before starting a new routine to see if you have any exercise limitations. If you’re planning exercise more intense than walking and you have certain risk factors or conditions (such as high blood pressure, high cholesterol, heart disease, kidney problems), your doctor may also recommend that you undergo exercise stress testing, which involves walking fast on a treadmill while your heart is monitored. But most people with diabetes don’t need this test.
If you have health issues such as foot problems, eyesight issues, arthritis or other limitations, your doctor can help you tailor an exercise plan that works for you or can refer you to a diabetes educator or an exercise physiologist who can help. It’s a good thing that exercise is so safe, because it’s so beneficial for people with diabetes.