Heart rate variability is not associated with multiple chemical sensitivity in a cross-sectional population-based study - The Danish study of functional disorders.

Objective: Multiple chemical sensitivity (MCS), a functional somatic disorder (FSD), is a multisystem, polysymptomatic disease, characterized by various individual symptoms attributed to low level of volatile chemical exposures. Symptoms relate to the autonomic nerve system (ANS) among others which is mandatory in the MCS delimitations. An accepted measure of ANS is heart rate variability (HRV). The aim was to explore associations between HRV and MCS in the general Danish population.

Methods: In the Danish Study of Functional Disorders, 7493 adults filled in questionnaires and participated in a physical health examination (2012-2015). The "E motion" heart rate monitor device assessed time and frequency measures of HRV. For this study, 143 were categorized with MCS of which, 84 were subcategorized as MCS without comorbid FSD. The remaining population (n = 5525) was used as comparison group. Logistic regression models to assess odds ratio (OR) with 95 % confidence intervals (95 % CI) of MCS, and MCS without comorbid FSD for each HRV exposure adjusted for age, sex, and chronic stress.

Results: Compared to the general population, median resting heart rate was higher (64.7 vs 63.1 bpm, p = 0.007) and median normal-to-normal intervals was lower (930 vs 952 ms, p = 0.007) in MCS individuals. Resting heart rate was associated with MCS (OR: 1.019, 95 %CI: 1.003; 1.037); but not after adjustment for chronic stress. No other associations with other HRV measures nor in MCS without comorbid FSD were found.

Conclusion: HRV was not associated with MCS. The magnitude of the differences between groups was small and of uncertain clinical significance.