The gut microbiome is a complex, ever-shifting collection of microbes that mediates much of the interaction between diet and health. This microbiome changes with age. The exploration of these changes is still a comparatively young field of research, even while expanding considerably in recent years. As we age, some of the beneficial species that produce useful metabolites decline in number, while some of the harmful species that can cause chronic inflammation prosper and expand. Chronic inflammation is an important aspect of degenerative aging, driving development and progression of all of the common age-related conditions.
The underlying causes of age-related changes in the gut microbiome are numerous, interacting, and complicated. It is yet to be determined which are the most important. Older people tend to eat a different diet and be more sedentary than younger people. They have age-damaged immune systems less capable of destroying unwanted microbes. Their gut lining is also less effective at keeping microbes out of tissues where they will cause an inflammatory reaction. All of these issues seem likely to contribute to a sizable degree, but much remains to be explained, such as the major shift in the gut microbiome that occurs in the mid-30s, long before most aspects of degenerative aging become significant.
What can be done about this problem of the aging gut microbiome? Setting aside any consideration of targeting the root causes, one blunt solution, which has done quite well in animal studies, is fecal microbiota transplantation from young individuals to older individuals. In aged killifish, this intervention restores a more youthful gut microbiome, improves health, and extends life span. The other blunt solution is less well explored, which is to deliver that same mix of youthful microbial populations in high volume as oral probiotics. This would require considerably more ingested material and a different mix of microbial populations than is presently marketed to consumers under the heading of probiotic supplements, but it seems quite plausible as a way forward.
Aging is recognized as a common risk factor for many chronic diseases and functional decline. The newly emerging field of geroscience is an interdisciplinary field that aims to understand the molecular and cellular mechanisms of aging. Several fundamental biological processes have been proposed as hallmarks of aging. The proposition of the geroscience hypothesis is that targeting holistically these highly integrated hallmarks could be an effective approach to preventing the pathogenesis of age-related diseases jointly, thereby improving the health span of most individuals.
There is a growing awareness concerning the benefits of the prophylactic use of probiotics in maintaining health and improving quality of life in the elderly population. In view of the rapid progress in geroscience research, a new emphasis on geroscience-based probiotics is in high demand, and such probiotics require extensive preclinical and clinical research to support their functional efficacy. Here we propose a new term, "gerobiotics", to define those probiotic strains and their derived postbiotics and para-probiotics that are able to beneficially attenuate the fundamental mechanisms of aging, reduce physiological aging processes, and thereby expand the health span of the host.
We provide a thorough discussion of why the coining of a new term is warranted instead of just referring to these probiotics as anti-aging probiotics or with other similar terms. In this review, we highlight the needs and importance of the new field of gerobiotics, past and currently on-going research and development in the field, biomarkers for potential targets, and recommended steps for the development of gerobiotic products. Use of gerobiotics could be a promising intervention strategy to improve health span and longevity of humans in the future.