Does your gut affect your risk for Alzheimer's disease?

January 1, 2024

Q. I know that your genes and lifestyle can influence your risk of getting Alzheimer's disease. Now I read that microbes in our guts also may be involved. Really?

A. Genes and lifestyle both influence our risk of getting Alzheimer's disease. And, as strange as it may seem, so may the microbes in our gut.

We've known for nearly 200 years that microbes live on and in us. We thought they were just living off the warmth and nutrients that our bodies provided to them — invisible freeloaders that had no effect on our health. Beginning about 20 years ago, we began to learn that was wrong. Like humans, microbes have genes. All of the different genes of the microbes that live on us or in us, collectively, are called our "microbiome." To our surprise, we've learned that these microbe genes can make chemicals that can affect human health.

We now know that our microbiome can affect our risk for obesity, diabetes, atherosclerosis, and other important diseases. A study reported in October 2023 in the prestigious scientific journal Brain finds that our microbiome may even influence our risk of developing Alzheimer's disease.

Previous studies had reported that in people with Alzheimer's disease, some particular species of gut bacteria are more prevalent, while other species are less so, compared to people without the disease. But that did not answer the cart-and-horse question: does the disease affect the difference in the gut bacteria, or does the difference in the gut bacteria affect the disease?

The new study provides provocative evidence that the gut bacteria may actually influence the risk of getting the disease. The research team took a group of healthy young rats and eliminated all bacteria from their guts. Then the team collected bowel movement samples from people with Alzheimer's disease and from people with normal cognition and no signs of the disease. Such samples are full of gut bacteria. Then the samples from humans were squirted into the rats' guts.

The microbiome from people with Alzheimer's disease — but not the microbiome from people without the disease — caused some Alzheimer's-like changes in the rats' brains. Those rats also developed memory impairments. Moreover, the rats that received the microbiomes from the most severely affected Alzheimer's patients developed the greatest brain abnormalities and memory problems.

It will require much more research to confirm that our gut microbiome influences our risk of Alzheimer's disease—and, if so, how it does so. The answer to that last question could someday point to treatments that can treat or even prevent Alzheimer's disease.

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