Impact of heart rate variability on C-reactive protein concentrations in Japanese adult nonsmokers: The Toon Health Study

Objective: Lower heart rate variability (HRV) is associated with the inflammation that is linked with the progression of atherosclerosis. We examined this association, taking insulin sensitivity into consideration, as it is related to both HRV and inflammation. Methods: Subjects were 1728 individuals ages 30-79 years who did not smoke between 2009 and 2012. C-reactive protein (CRP) concentrations and white blood cell (WBC) counts were assessed as markers of inflammation. The homeostasis model assessment index for insulin resistance (HOMA-IR) and Gutt's insulin sensitivity index (ISI) were calculated based on fasting and 2h-post-load glucose and insulin concentrations in a 75-g oral glucose tolerance test. Pulse was recorded for 5 min, and time-domain HRV indices of standard deviation of NN intervals (SDNN) and root mean square of successive differences (RMSSD) were calculated. Power spectral analysis provided frequency domain measures of HRV: high frequency (HF) power, low frequency (LF) power and LF/HF. Results: Sex and age-adjusted logistic models presented quartiles of SDNN, RMSSD, LF, and HF significantly associated with the highest quartile of CRP or WBC. After adjustment for body mass index and ISI, the associations were attenuated for WBC; however, even after further adjustment for several variables, SDNN, RMSSD, LF, and HF remained significantly associated with elevated CRP concentrations. When results were stratified by weight, the associations appeared more evident among non-overweight individuals. Conclusion: Lowered HRV, primarily due to parasympathetic dysfunction, was associated with elevated inflammation, independent of weight, insulin sensitivity, and other related factors.