BACKGROUND

Our primary aim was to investigate the associations that components of metabolic syndrome and physical activity have with cardiac autonomic nervous system activity as estimated by heart rate variability (HRV) in young adults free of metabolic abnormalities. We also aimed to identify predictors of 3-year changes in HRV.

METHODS

Physical activity was assessed annually in 163 healthy participants over 3 years (2008-2010). Components of metabolic syndrome measured annually were; waist circumference, systolic blood pressure, high-density lipoprotein, triglycerides, glucose, and C-reactive protein. A linear mixed regression model was used to assess associations between HRV, metabolic syndrome components and physical activity. Linear regression was used to identify predictors of changes in HRV.

RESULTS

Metabolic syndrome components were negatively associated with HRV indices and higher heart rate, while physical activity was associated with higher HRV and lower heart rate. Physical activity and inflammation were predictors of positive and negative changes in HRV indices, respectively.

CONCLUSIONS

In participants without significant metabolic abnormalities, metabolic syndrome components were still associated with less favourable HRV profiles. Physical activity and inflammation were both able to predict changes in HRV, albeit in different directions. It appears that the process of autonomic dysfunction starts at a young age and may be mediated in part by inflammation. Metabolic syndrome prevalence is increasing in younger populations; promoting the metabolic and autonomic benefits of exercise remains imperative.