Greater loneliness is associated with lower cognitive function. Although preliminary evidence is promising, additional studies are necessary to determine the causality and biological mechanisms underlying the relationship between loneliness and cognitive function. Findings should be verified in culturally diverse populations in different ages and settings using biobehavioral approaches.

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Estrogen and testosterone may influence cognition in older adults, but the relationship between sex hormones and cognitive function is complex. The aim of this systematic review is to examine the role of sex hormones in cognitive function among older adults. A comprehensive, electronic review of literature was performed. Inclusion criteria were original quantitative research, written in English, used human subjects with a mean age of ≥60 years, and published from January 1997 through May 2012. Findings were mixed, although potential patterns were identified. Estradiol levels were potentially associated with benefits to episodic memory, semantic memory, verbal memory, and verbal learning in females only. The association between testosterone and cognitive function was mixed in both genders. Mixed findings may have been influenced by methodological differences and future studies should include research designs with ample rigor, sufficiently powered samples, consistent cognitive measurements, and clear descriptions of handling and storage of biological specimens.

Background: Companion animals may reduce depression and loneliness in socially