About 900 of these people were seniors who were regularly examined in medical clinics to assess their health. Dr. Gibbons and his colleagues found that middle-aged people from around 40 years of age showed significant changes in their microbiomes. The strains that were most dominant in their guts tended to decrease while other, less common strains were more common, causing their microbiomes to diverge and become increasingly different from others in the population.
“We have found that people drift apart in the different decades of their lives – their microbiomes are becoming more and more unique,” said Dr. Gibbons.
People with the most changes in their microbial makeup tended to have better health and longer lifespans. They had higher levels of vitamin D and lower levels of LDL cholesterol and triglycerides, a type of fat in the blood. They needed less medication and had better physical health, faster walking speeds, and greater mobility.
The researchers found that these “unique” individuals also had higher levels in their blood of several metabolites produced by gut microbes, including indoles, which have been shown to reduce inflammation and maintain the integrity of the barrier that lines the gut and protects. In some studies, scientists have found that giving indoles to mice and other animals helps them stay youthful so that they are more physically active, more mobile, and more resistant to disease, injury, and other stresses in old age. Another metabolite identified in the new study was phenylacetylglutamine. It is not exactly clear what this connection does. However, some experts believe this promotes longevity, as research has shown that centenarians in northern Italy tend to have very high levels.
Dr. Wilmanski found that people whose gut microbiomes had barely changed with age were in poorer health. They had higher levels of cholesterol and triglycerides, and lower levels of vitamin D. They were less active and couldn’t run as fast. They took more medication and died almost twice as often during the study period.
The researchers speculated that some intestinal bugs, which might be harmless or even beneficial in early adulthood, might become harmful in old age. For example, the study found that healthy people who saw the most dramatic changes in their microbiome composition dropped sharply in the prevalence of bacteria called Bacteroides, which are more common in developed countries, where people eat many processed foods full of fat, sugar, and salt and less common in developing countries, where people tend to eat higher fiber diets. When fiber is not available, according to Dr. Gibbons like to “mucus,” including the protective layer of mucus that lines the intestines.
“Maybe that’s good if you’re 20 or 30 years old and you have a lot of mucus in your gut,” he said. “But as we get older, our mucus layer gets thinner, and maybe we need to suppress these mistakes.”