Dear Running Doc:
You have got to help me, Doc. Last month I ran a marathon in 4:32. I collapsed and passed out at the finish line. I drank sports drink when I was thirsty and used Gu four times during the race. For the last 15 years I have done the same thing without a problem. I am 48 and run approximately 60 miles per week. I woke up in the hospital and they said I was dehydrated. They gave me fluids, I felt fine and went home. One interesting fact was that they found my sugar was equal to 338 and had to give me insulin to bring the sugar down. I have since gone to an endocrinologist who said I am not diabetic after running many blood and urine tests. He said he could not understand why my sugar was elevated. Do you know?
Emily P., Durham, NC
Thanks for writing, Emily. Your sugar elevation has been seen by many marathon medical directors throughout the world. Unfortunately, there is only theory why this happens. New research is being done throughout the world and I will keep everyone informed when an answer is found. Here are the theories:
The kidney filters glucose and re-absorbs it. Once the sugar is above 180 it is too much for the kidney to handle leading to elevated glucose in the blood and urine. By osmotic effect, that forces the kidney to secrete more water and produce more urine leading to dehydration.
The blood sugar value that leads to sugar in the urine is called the renal threshold for glucose.
One of the new diabetes drugs (SGLT2 inhibitors) works by lowering the renal threshold for glucose and causes glucose in the urine earlier than 180. That extra fluid loss from that drug causes blood pressure decrease and dehydration.
Endocrinologists say that the kidney does not metabolize glucose and a non-diabetic should be able to metabolize glucose no matter how much sugar you eat and drink during a marathon. I would like to point out here that 35 years ago renal doctors used to say that you could drink as much water as you want during a race and a healthy person should be able to handle it.
We later found out that running long distance changes kidney physiology and drinking too much (sports drink or water) could cause hyponatremia (loss of blood sodium). Could sugar metabolism be changed while running a long-distance race? That is what the research being done is aiming to find out.
What should all runners do in the meantime? The prudent thing to do is cut your Gu or gel down by half and don’t drink all sports drink. Indeed, it can’t hurt to cut down on sugars (which you do need some) by half as we await the results of the research study.
Other theories include alterations in hormones while you run. There are many reasons that these increased sugar levels in blood and urine could happen. The International Marathon Medical Directors Association (IMMDA) are on it and hopefully will have an answer within the year.
I hope this helps Emily. Let me know if you have any other questions.
Enjoy the ride!
Lewis G. Maharam, MD, FACSM is one of the world’s most extensively credentialed and well-known sports health experts. Better known as Running Doc™, Maharam is author of Running Doc’s Guide to Healthy Running and past medical director of the NYC Marathon and Rock ‘n’ Roll Marathon series. He is Medical Director of the Leukemia & Lymphoma Society’s Team in Training program. He is also past president of the New York Chapter of the American College of Sports Medicine. Learn more at runningdoc.com.
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