Updated February 29, 2016
You can think of exercise as a great blood-sugar-lowering drug.

You can think of exercise as a great blood-sugar-lowering drug.(HEALTH/ISTOCKPHOTO)

Exercise causes blood sugar to go down—except when it doesn't. In some cases, blood sugar can temporarily increase with exercise.

Maddening? Yes. Like so many aspects of type 2 diabetes, your body's response to exercise can be highly individual.

The time of day you exercise may affect blood sugar
Blake Holden, of Brooklyn, N.Y., finds his blood sugar can vary depending on the time of day he is exercising. "When I exercise in the morning, go for a run, my blood sugar spikes big time. I'm not sure why that happens. But in the evening, it doesn't; it drops."

That's why it's crucial to monitor your glucose levels before and after your workout (after getting clearance from your doctor). Ideally, you should check your blood sugar each time you exercise, says Ann Albright, PhD, director of the Division of Diabetes Translation at the Centers for Disease Control and Prevention in Atlanta.

But, if that proves to be a huge barrier that keeps you from exercising, then it's probably OK to do it a few times when you first start or restart your exercise routine until you get a feel for how your blood sugar reacts to exercise, Albright says.

Consistency is crucial
Choose a regular exercise routine and stick to it as often as possible. This can result in consistently lower blood sugar (exercise can cause a drop in blood sugar for up to 12 to 24 hours).

"It is really important to have a consistent exercise plan that you can do five days a week," says Virginia Valentine, a certified diabetes educator at the Diabetes Network, Inc., in Albuquerque, N.M.

"If a person is a couch potato all week and tries to jump into a significant activity for a few hours on the weekend, it could cause blood glucose that is too low or even an injury."

Blood sugar is more likely to go too low and cause hypoglycemia in people who take insulin or certain diabetes medications (such as sulfonylureas).

If you are taking such drugs, you need to be extra careful about monitoring your blood sugar and carry food or glucose tablets so that you can treat hypoglycemia if it occurs. If you aren't taking medication, then hypoglycemia is less of a concern.