Here are some sobering facts. Around 795,000 people have a stroke each year, which equates to a stroke every 40 seconds. Stroke is the fifth-leading cause of death in the United States, and it kills 140,000 people each year, which is one death every four minutes. The South has the highest death rates from stroke in the United States.

Advancing age is a huge risk factor for stroke. About 66 percent of stroke victims are older than 65. After age 55, the number of strokes doubles with every decade of life.

There are several types of stroke, but the most common are ischemic strokes. This is where a blockage in a blood vessel prevents blood flow to areas of the brain. Those brain cells don’t receive oxygen, and they die.

Recovery from a stroke is possible, but worldwide, 65 percent of survivors have life-altering permanent issues, including loss of full mobility, speech alterations or cognitive impairment.

The financial toll on families and our medical systems is staggering: $34 billion annually. Advances in medical care make surviving a stroke more likely, but there are still significant recovery times, and many live with neurological issues.

Aging processes can alter our normal brain functions and even result in the loss of some brain cells. These changes can delay a person’s recovery from a stroke.

Other changes occur with age. We now understand that the microbes (bacteria, fungi and viruses) that live in our gut change with age. Two major groups of bacteria in our microbiome are the Bacteroidetes and Firmicutes.

Aging increases the proportion of the Firmicutes, which has been linked to diseases like heart disease, diabetes and dementia. Our small friends are turning on us.

After a stroke, immune cells move to the damaged brain site from across the body, including the gut. The gut is the second largest source of immune cells in the body. These immune cells release chemicals that create inflammation, which contributes to the brain damage observed after stroke.

In some experiments, scientists transferred the microbiome of young healthy mice into the gut of aged mice. When the mice had a stroke, fewer mice died and others recovered more quickly. Immune cells associated with inflammation were reduced and fewer were found in the brain.

This means the younger microbiome was protecting the animals from additional brain damage after stroke, and changing the way immune cells act could help even more.

Research now focuses on identifying the source of the damage: either a harmful chemical produced by aged microbiome or a protective chemical produced by young healthy microbiomes. These diverse microbes produce a vast variety of metabolic chemicals, so picking one out is hard.

Scientists have focused on molecules called short chain fatty acids, which are reduced with aging and after a stroke. Bacteria producing these short chain fatty acids also improved the recovery from a stroke. This finding could lead to new therapies.

We hopefully are moving where we can harness our single-celled microbe friends to manage this devastating disease.

Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at

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