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From Kansas City, Missouri, USA:

I have been training for a marathon, which I plan to run in the fall, for 10 weeks now. I want to know what my ideal glucose level should be prior to starting the marathon. I will be drinking six to eight ounces of a sports drink every two to three miles during the race.


The ideal pre-exercise number for an athlete is individualized, like diabetes in general. The guidelines used by the ADA (American Diabetes Association) and ACSM (American College of Sports Medicine) are to delay exercise if your blood sugar is 250 mg/dl [13.9 mmol/L] or higher with ketones. A blood sugar below 100 mg/dl [5.6 mmol/L] warrants some carbohydrates to increase the level.

The ideal level should fall within these guidelines and experimented with leading up to the marathon. Some athletes feel sluggish with levels above 180 mg/dl [10.0 mmol/L] while others may do fine in the mid 200s mg/dl [around 13.9 mmol/L]. If drinking six to ounces of sports drink every two to three miles works best, go with it. Just remember that sports drinks are different in carbohydrates. For example, Gatorade has 14 grams of carbohydrates in every eight ounces, while PowerAde has 19 grams for every eight ounces. That may not be a big deal for one cup, but multiply it over a full marathon and it may throw off calculations significantly. It may be a good idea to check with race officials about the type of sports drinks served along the race. If PowerAde is one of the sponsors, it is a good bet that is being served at the water stops along the race route.

Remember that marathoners often find it difficult to control high blood sugars prior to the start due to the anxiety or competitive feeling they get. Try drinking some water and practicing some stress management techniques rather than using insulin. Many times, once the race has started and nerves calm down, high blood sugars will subside.


Original posting 7 Jul 2006
Posted to Exercise and Sports


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Last Updated: Tuesday April 06, 2010 15:10:08
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