Insomnia is a chronic mental health condition characterized by difficulty initiating and maintaining sleep with a prevalence of over 50% in Israeli adults ages 65 and above. It is associated with increased risks for chronic illnesses (e.g., cardiovascular disease), poor mental health (e.g., anxiety and depression), functional limitations, and cognitive decline. Available pharmacological and behavioral treatments focusing on reducing nighttime hyper-arousal offer limited success, and it appears that there is no "one size fits all" treatment for late life insomnia. Mounting evidence suggests that sleep is related to metabolic status, however, studies on the associations between sleep and dietary patterns are surprisingly scarce.

The ability of gut microbiota to communicate with the brain is emerging as an exciting concept in health and disease and provides the rationale for the present project. Findings demonstrate that gut microbiota modulates mental capacities such as brain plasticity and cognitive functions in older adults, as well as stress related mental illness. The composition of the intestinal microbiota in older people (>65 years) differs from the core microbiota and diversity levels of younger adults. With age, gut populations of beneficial microbes show a marked decline. As diet has been shown to markedly promote microbiota biodiversity, it is hypothesized that diet-induced changes in microbiota may provide a novel approach for the treatment of mental health. Although insomnia is strongly linked to mental health (e.g., depression and anxiety), as well as cognitive and motor performance, the effects of diet-induced microbiota alterations, based on individual microbiota composition, on late life insomnia is currently unknown.

The proposed project will be the first to investigate the associations between gut microbiota and sleep, and assess the potential of a six-months personalized, diet-induced microbiota alterations intervention (PDM), aimed to improve insomnia in older adults. We will also look at cognitive, motor and mental health factors as possible mediators in this relationship. Specifically, we will test the associations between microbiota composition and sleep quality, both cross-sectionally and longitudinally, i.e., following a PDM intervention; evaluate the impact of PDM on changes in cognitive, motor and mental health functions; and identify the mediating roles of changes in cognitive, motor and mental functioning on the effects of a PDM intervention on sleep quality. Findings are expected to improve the quality of life of older adults by enhancing their sleep, functional status, mental health and overall wellbeing.

Inclusion Criteria:

• Based on DSM-5 criteria of diagnosed chronic insomnia in adults, participants will be included if they report difficulties in initiating or maintaining sleep or early morning awakening at least three nights per week that lasts for a minimum of three months, and impaired daytime functioning.

Exclusion Criteria:

• Based on standard clinical history questionnaires and sleep questionnaires, participants will be excluded if they are less than 65 years, have any significant visual or hearing impairments or chronic pain, if they have or had significant and unstable medical, neurological, or psychiatric illness, if they are alcohol or drug abusers or taking psychiatric medication, or if they had sleep apnea syndrome (SAS) or periodic limb movement disorder during sleep (PLMD).