**7. Conclusions**

Gut-brain axis is a bidirectional chemical network sending information between the intestine and the brain via soluble, chemical messages as well as nervous sympathetic and parasympathetic inputs. A third player with a determinant role in the health of both systems is the gut microbiota. Aging affects all players of the microbiota-gut-brain axis, leading to modified composition of bacterial taxa, chronic low-grade inflammation, modified intestinal metabolism, resulting in diminished availability of neurotransmitters or neurotransmitter precursors and short-chain fatty acids. Along with synaptic impairment, oxidative stress and neuroinflammation, aging leads to behavior alterations, anxiety and cognitive impairment. Interventions on gut-brain axis with nutraceuticals (food or food-derived products that have putative beneficial effects) alleviate some age-associated behavioral and cognitive alterations, as repeatedly demonstrated in animal models. Recently, clinical trials have begun to explore the beneficial effect of gut-brain axis modulation, in mood or cognition-associated disorders. Upon reports of positive results, gut-brain axis emerges as an important, easy to access target for promoting a healthy brain aging.
