The human gastrointestinal tract is an extremely complex ecosystem where microbiota, nutrients, and host cells are inhabited by an abundance of heterogeneous microorganisms, such as bacteria, viruses, protozoa, fungi, and their collective genetic material, residing as beneficial symbionts, innocuous commensal microbiota, or pathogenic microbes.1
The gut microbiome and its role in both health and disease have been the focus of extensive research, establishing its involvement in human nutrition, metabolism, physiology, and immunoneurohormonal systems. Current findings suggest potential connections between the microbiome and many health conditions including metabolic disorders, obesity, inflammation, and cancer.2 Although studies have shown that the gut microbiome has important effects on human health, its importance in human aging is still being realized.
EVOLUTIONARY DEVELOPMENT OF MICROBIOTA
Throughout the human life span, the activity of the gut microbiome has shown predictable patterns, with rapid change in early life (0-3 years), followed by a period of stability until middle age, and then accelerated change beginning in late adulthood, ending with gradual changes associated with advanced age.3,4 In populations 65 years and older, studies have revealed several associations between gut microbiome composition and measures of frailty,5 physical fitness,6 and diet,7 emphasizing the importance of proper gut microbiome function with the progression into the latter years of life. Identifying age-related patterns within the gut microbiome has the potential to monitor and modify gut microbiome health throughout the human life span.
GUT MICROBIOME IN HEALTHY AGING2
Aging is inevitable; however, the deleterious effects of aging on physical and mental function are not universal. Healthy aging is experienced by many individuals across the globe. The factors that determine healthy aging include genetic, environmental, and lifestyle considerations. Of these factors, an individual's lifestyle offers an opportunity for intervention, as well as improved health.
Studies have found gut microbiome pattern differences between older adults who are lean and physically active compared with their less fit and healthy counterparts. In addition, research has connected early development of frailty with less microbial diversity.
A recent study demonstrated that beginning in mid-to-late adulthood, gut microbes become increasingly unique to individuals. This cohort study consisted of more than 9000 individuals and found that compositional uniqueness of the microbiome is strongly related to microbe-produced amino acid derivatives located in the bloodstream.2 Healthy individuals older than 80 years show a microbial progression toward a unique composition, whereas this gradual movement toward microbial uniqueness is absent in individuals who are not as healthy. More specifically, the identified microbiome pattern of healthy aging is characterized by a depletion of the core genera found across most humans, primarily Bacteroides, Roseburia, and Faecalibacterium, which may vary across different human populations. This study indicates that retaining this high core microbial dominance into older age, or having a low gut microbiome uniqueness, is indicative of decreased survival. Therefore, increasing compositional uniqueness of the gut microbiome is a key component to healthy aging.
SUMMARY
Physical and cognitive decline with age is not experienced universally. Healthy aging is evident in many individuals throughout the world. Research has shown that aging-related health decline has been correlated with changes in different microbiome states. Those individuals with a higher level of microbiome uniqueness exhibit greater overall health.
There are many variables that determine healthy aging, such as genetics, environment, and lifestyle factors. Among these, an individual's lifestyle offers an opportunity for improving health and well-being, by making healthy dietary choices and engaging in physical activity.
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