I have type 1 diabetes and ride a mountain bike 10 miles after work three days a week and 30 miles a day on weekends. What does riding a mountain bike year round do to the sugar levels?

Your blood sugar response to exercise will depend on a number of factors, including type and amount of circulating insulin, intensity of exercise, and time of exercise in relation to insulin peak action time. Generally, aerobic exercise such as mountain biking will decrease blood sugars when no compensating decrease in circulating insulin levels is possible. With intense exercise, insulin pump users who decrease basal rates or suspend insulin delivery may actually observe a rise in post exercise blood sugars.

The only way to know your own blood sugar response to exercise is to pattern the change by measuring sugar levels before, during, and after exercise. This will allow you and your healthcare team the ability to make appropriate decisions regarding possible insulin adjustments or carbohydrate intake. Active persons with insulin dependent diabetes who are unable to decrease circulating insulin levels generally require 15-30gms of carbohydrate for each 30 minutes of moderate intensity aerobic exercise. You would be wise to bring both your glucose meter and an adequate source of carbohydrate with you on your ride to prevent hypoglycemia.

As a further resource, you may find the book, The Diabetic Athlete by Sheri Colberg, Edward Horton to be helpful.

DMW