Metabolic Syndrome and Dementia Risk in Older Adults: A Narrative Review.

Dementia is a major global health issue in aging societies. Metabolic syndrome (MetS), a cluster of metabolic abnormalities, has been proposed as a modifiable risk factor for dementia, although existing evidence remains inconsistent. This review examined recent studies on the association between MetS and dementia risk in older adults. We searched PubMed for original studies published between January 1, 2014, and July 15, 2024, using the keywords "metabolic syndrome" and "dementia." Fourteen studies met the inclusion criteria: five retrospective cohort studies, two prospective cohort studies, four cross-sectional studies, two bioinformatics studies, and one meta-analysis. Overall, MetS was associated with adverse cognitive outcomes, with relatively more consistent evidence for vascular dementia and progression from mild cognitive impairment to dementia than for Alzheimer disease. Hypertension, abdominal obesity, and low high-density lipoprotein cholesterol were associated with adverse cognitive outcomes in some studies, although component-specific findings varied across studies. Temporal patterns of MetS also appeared to be relevant, with some studies reporting higher dementia risk in individuals with worsening or persistent metabolic burden, although findings after MetS resolution were not consistent. Several studies also reported deficits in executive, attention, and visuospatial function. Bioinformatics studies suggested possible genetic links, including overlap with apolipoprotein E-related pathways, although evidence remains limited. MetS may represent a clinically relevant risk marker for adverse cognitive outcomes in older adults, although its association varies according to MetS definition, study population, and cognitive outcome. Further large-scale studies are needed to clarify the underlying mechanisms and subtype-specific associations.