A specific species of gut bacterium may help explain why some older adults hold onto muscle strength longer than others, according to a study that combined data from human volunteers with follow-up experiments in mice.
Researchers from Leiden University Medical Center, working with collaborators in Groningen, Granada, Almería, Valencia and Cádiz, analyzed gut microbiome samples from 90 younger adults and 33 older adults whose muscle strength had been carefully measured through handgrip, leg press and bench press testing. Published August 21 in the journal Gut, the study found that the abundance of one microbe in particular, Roseburia inulinivorans, tracked closely with strength — but only that species, not its close relatives.
From association to mice
Among older adults, those carrying higher levels of R. inulinivorans had roughly 29 percent greater handgrip strength than those with little or none. In the younger group, higher levels of the bacterium were linked to both stronger grip and higher VO2 peak, a measure of aerobic fitness. The researchers, led by Borja Martinez-Tellez, also noted that the bacterium tends to become less abundant with age, raising the question of whether its decline contributes to age-related muscle loss, a condition known as sarcopenia.
To test whether the bacterium does more than simply correlate with strength, the team gave it to mice over an eight-week period. Treated mice developed about 30 percent greater forelimb grip strength than untreated animals, along with larger muscle fibers and a higher proportion of fast-twitch fibers, the type recruited for quick, powerful movements. According to coverage of the findings, the bacterium appeared to change how muscle cells used certain metabolic building blocks and activated energy-related pathways inside the tissue.
The authors are careful to flag the limits of what the mouse experiments show. None of the human-derived Roseburia strains permanently colonized the mice's guts, meaning the effects came from a temporary presence of the bacterium rather than lasting colonization, and the exact biological mechanism connecting gut microbes to distant muscle tissue remains only partly mapped; the team did not directly measure inflammation markers or nerve-to-muscle signaling, both plausible pathways. The researchers describe the bacterium as a promising lead for a future nutraceutical or probiotic approach to muscle wasting, and have secured a patent, but stress it is not close to ready for human use. Larger, longer-term human studies — ideally testing whether boosting the bacterium changes strength over time, rather than just observing who already has it — are still needed before any such conclusion can be drawn.
