Ask the Doctors

Dear Doctor: Does insulin resistance increase as we age? I just read it has something to do with the gut. Why would that be true?

Dear Reader: To talk about insulin resistance, we should start with insulin. It’s a hormone produced by the pancreas that helps to make glucose available to the body, which uses it for energy. After you eat, as your body digests the food, glucose is released into the blood. The pancreas then releases insulin. This hormone makes it possible for muscle, fat and liver cells to absorb glucose. When your insulin metabolism is working properly, cells get the building blocks they need to produce energy, and the level of glucose in the blood remains within a healthy range.

One way things can go awry is insulin resistance. This means that even though the pancreas releases insulin into the blood, the fat, muscle and liver cells don’t respond properly to the hormone. This leaves too much glucose in the blood, which prompts the pancreas to release even more insulin. As long as the beta cells of the pancreas remain capable of producing the extra insulin that the muscle, fat and liver cells now need, blood sugar levels will remain in a healthy range. But once the pancreas can no longer keep up with the increased demand for insulin, the resulting extra blood glucose can lead to an individual developing Type 2 diabetes.

It’s estimated that up to 1 in 3 Americans, including half of people age 60 and up, experience insulin resistance. Last year, the results of a study published by scientists at the National Institute on Aging shed light on possible reasons for the link between age and insulin resistance. For answers, the researchers turned to the gut. Specifically, they became interested in the fact that despite differences in ethnicity, geographic location and the contents of their diets, people had similar changes to their gut microbiomes as they aged. One of these changes is a decrease in the healthy layer of mucus in the gut, which is needed for optimal production and absorption of nutrients. The health of this mucus layer relies, in part, on a specific beneficial bacterium known as Akkermansia muciniphila, or Akk.

While studying mice, and then rhesus monkeys, researchers found that aging was associated with a drop in levels of mucus-friendly Akk. This triggered a series of events that gave rise to certain immune cells, which were linked to insulin resistance. When levels of Akk bacteria were restored to normal, the insulin metabolism in the animals returned to normal as well.

The research is exciting because it opens up new avenues of inquiry into the problem of insulin resistance. It’s good news because Type 2 diabetes has already reached epidemic proportions around the world. Now, with a rapidly aging population, novel therapies to maintain a healthy insulin metabolism are more important than ever.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

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