The influence of age and body mass index on the metabolic syndrome and its components

The aim of this study was to evaluate the influence of ageing and body mass index (BMI) on the revised National Cholesterol Education Program (NCEP)-defined metabolic syndrome, its components, diabetes and coronary heart disease prevalence using the Third National Health and Nutrition Examination Survey.

Data from adults aged 20 and older who received morning physical examinations after a fast of at least 9 h (n = 7959), representing 196.8 million Americans were used in this analysis. The population was stratified by age deciles and BMI categories using standard definitions of overweight and obesity. Due to small sample size, those few individuals with BMI <18.5 were excluded.

Fasting glucose, diabetes and systolic blood pressure (SBP) seem to have a linear relationship with age and BMI, that is, increasing BMI seems to linearly reduce the age decile when the mean exceeds the NCEP cutpoint. Regardless of BMI, the prevalence of diabetes and hypertension increases with age. Triglyceride levels and prevalence of metabolic syndrome follow a pattern that is less linear. Fasting insulin and C-reactive protein (CRP) levels correlate better with BMI than age. Diastolic BP and HDL cholesterol for men and women (analysed separately) did not correlate with either age or BMI.

For each component of the metabolic syndrome and associated factors, there is a complex interaction between ageing and obesity. Some components are associated with obesity but not ageing (e.g. CRP), while others are associated with both obesity and ageing (e.g. glucose). Even when the association exists, the specific relationship can appear to be more (e.g. SBP) or less (e.g. triglycerides) linear.