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Originally published November 26, 2019, last updated December 2, 2019
The microbiome, the community of bacteria living in and on us, most prominently in our gut, is an increasingly popular area of study. Scientists are discovering many ways that microorganisms in our gut can influence our health. Here are three of the latest findings.
1. Gut bacteria may alter the aging process.
A research team that transplanted gut microbes from old mice (24 months old) into young, germ-free mice (six weeks old) found that after eight weeks, the young mice had increased intestinal growth and production of neurons in the brain. The team showed that this was due to an enrichment of gut microbes that produce a specific short chain fatty acid called butyrate. Butyrate is produced by microbial fermentation in the large intestine and stimulates production of a pro-longevity hormone. As we age, butyrate production is reduced. Giving butyrate on its own to the young germ-free mice produced the same adult neurogenesis effects, the researchers showed.
While further research is necessary, the new study raises the prospect that healthy aging could be promoted either through dietary products that enhance butyrate-producing microbial populations, or through direct butyrate supplementation.
2. Parkinson’s disease may start in the gut, not the brain.
A growing body of evidence links Parkinson's disease to the gastrointestinal tract, opening new possibilities for treatment.
Parkinson’s disease is a neurodegenerative disorder that affects predominately dopamine-producing neurons in a specific area of the brain called substantia nigra, the part that controls movement. The damage can cause symptoms that can include tremor, limb rigidity, slowness of movement, and gait and balance problems, as well as emotional problems such as depression, constipation, sleep disruption and emotional changes.
While an exact cause is not known, a distinguishing feature of Parkinson’s disease is the accumulation of toxic clumps of alpha-synuclein protein called Lewy bodies. Some scientists have proposed that these toxic proteins form in the peripheral nervous system (PNS) of the gut and spread to the brain, which is part of the central nervous system (CNS), via the vagus nerve. The vagus nerve is a bundle of fibers connecting major organs to the brainstem, which joins the spinal cord to the brain.
Researchers have demonstrated that alpha-synuclein fibers injected into the gastrointestinal tracts of rodents can traverse through the vagus into the brain. Most recently, investigators are testing a hypothesis about targeting the enteric nervous system — which is embedded in the lining of the gastrointestinal system — with a compound that can inhibit the intracellular aggregation of alpha-synuclein. Such targeting, they think, could restore enteric functioning in the short term, and possibly slow the progressive deterioration of the central nervous system in the long term.
3. Gut bacteria may play a role in mechanisms related to muscle strength in older adults.
Researchers have studied the connection between the gut microbiome, muscle, and physical function of mice and younger adults, but few studies had been conducted with older adults. A new study by researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging aimed at finding which bacteria are directly related to increased lean mass and physical functioning in older adults.
In mice, when bacteria were transferred from the cecum, which connects the small intestine ot the colon, of healthy mice into germ-free mice, it resulted in a reduction of lean mass. In the recent study, researchers compared bacteria from the gut microbiomes of 18 older adults with high-physical function and a favorable body composition — meaning a higher percentage of lean mass and a lower percentage of fat mass — with 11 older adults with low physical function and a less favorable body composition. The study found higher levels of Prevotellaceae, Prevotella, Barnesiella, and Barnesiella intestinihominis — all potentially good bacteria in the high-functioning older adults and in the mice that were colonized with fecal samples from the high-functioning older adults. In earlier studies, Prevotella has been seen to be higher in young athletes and in stronger older adults, and both Barnesiella and Prevotella produce short-chain fatty acids that could be instrumental in improving muscle strength.