Microbiological Foundations to Optimise Intrinsic Capacity and Promote Healthy Ageing: An Integration Into the Life Course Approach.

The World Health Organization (WHO) defines healthy ageing as the process of developing and maintaining functional ability, comprising an individual's intrinsic capacity, the environment and the interaction of the two. The framework is based on a positive approach to ageing, giving value to the resources individuals can rely upon as they age and that they can build their physical, mental and social health, and overall well-being. To promote healthy ageing, it is important to understand better the biological mechanisms underlying this phenomenon from this positive perspective. Our knowledge about cellular processes that drive human ageing has increased dramatically, with current evidence identifying 12 hallmarks of ageing. Dysbiosis is one of these and is broadly defined as a 'deranged microbiological composition in and on the human body'. It is often measured by quantitatively and qualitatively evaluating the bacterial species in the gut. A major feature of dysbiosis and other markers of ageing is that these focus on age-related impairments, contributing to the onset of adverse outcomes over time rather than highlighting features that promote healthy ageing. Scientific literature addressing the hallmarks of healthy ageing, including those potentially positively affecting intrinsic capacity, is lacking. To this end, we propose the concept of gut eubiosis, the homeostatic state of commensal gut bacteria and their metabolites, as proof of concept, serving as a hallmark of healthy ageing. Importantly, this work adopts a life course approach to explore how a person's intrinsic capacities evolve with gut microbiota modifications at different life stages.