The aim of this study was to find out the prevalence of the different metabolic syndrome combinations and to evaluate their association with all-cause mortality in younger and older men and women. The study population was derived from the Third National Health and Nutrition Examination Survey (NHANES III) and included 2,784 men and 3,240 women with a follow-up of 14.2±0.2 years. Analyses revealed that age and sex differences were observed in metabolic syndrome phenotypes and their associations with mortality risk. Metabolic syndrome was present in 26% of younger (aged ≤65 years) and 55% of older (aged >65 years) participants. In women, waist circumference was often present in the more common combinations compared to men. The combinations were more heterogeneous in their presentation for men. All metabolic syndrome risk factors were more prevalent in the older than younger adults. However, the sex differences observed in the prevalence of the various metabolic syndrome factor combinations were largely abolished in older adults. Overall, the presence of all five metabolic syndrome factors was the most common metabolic syndrome combination in both older men and women. The associations between the different metabolic syndrome combinations and the mortality risk were different according to sex and age. Metabolic syndrome was associated with higher mortality risk in younger adults after adjustment for relevant covariates. However, no clear association between metabolic syndrome and mortality risk was observed in older men and women. These results suggest that metabolic syndrome is a heterogenous condition that must be carefully analyzed before quantifying its mortality risk.
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