Impact of metabolic syndrome on cognitive decline in older age: protective or harmful, where is the pitfall?

Metabolic syndrome (MetS) has been found to be a risk factor for dementia, mild cognitive impairment, and its associated states. However, a definitive conclusion cannot be drawn from the available data. Discrepancies between the results are due to several factors, e.g., study design, heterogeneity of the population enrolled, reliability and sensitivity of detection tools for cognitive changes, cut-offs and criteria used to diagnose MetS, the outcome measures considered, MetS duration before the onset of cognitive decline, and also the analytical approach performed. Recently, a systematic review and meta-analysis including 19,522 subjects aged 59-85 years from 13 longitudinal population-based studies has been conducted to examine the association between MetS and longitudinal changes in cognitive functions. While a marginal significant association was found in the younger old group, this relationship was not observed in older group (>70 years). It is not yet clear how age can influence this relationship. Apart from methodological issues, other biological factors are likely involved in this direction reversal.