Metabolic syndrome associated with lower heart rate variability in middle-aged male twins
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Higher cardiovascular mortality associated with metabolic syndrome may be related to abnormal modulation in autonomic tone. The study examined the association between metabolic syndrome and autonomic tone as measured by heart rate variability (HRV) among 288 twins participating in the Twins Heart Study. Across all frequency ranges, metabolic syndrome was associated with decreased HRV, each additional metabolic syndrome component being associated with lower HRV. After adjusting for potential confounders, very-low frequency, low frequency, and total power spectra of HRV remained significantly lower in twins with progressively higher number of metabolic syndrome components. When comparing each twin with his brother, a one-unit increment in metabolic syndrome components was associated with an 8% smaller very-low frequency and a 15% smaller low frequency spectrum among the 87 twin pairs who were discordant for the number of metabolic syndrome components. In conclusion, metabolic syndrome appears to be associated with lower HRV in middle-aged male twins even after controlling for genetic and shared environmental factors accounted for by comparisons within twin pairs. Abnormal autonomic tone as evidenced by lower HRV may be partly responsible for the higher rate of atrial fibrillation, coronary heart disease, cardiac death, and overall mortality observed in metabolic syndrome patients.
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