Markers of stress as predictors of wellbeing and workability

In order to prevent sickness absence and to maintain a safe and sound work climate, interventions may be needed in the workplace. Occupational Health Services (OHS) are special advisers, with the opportunity to suggest/perform interventions at individual and group level. The use of methods for evaluating changes in health is a precondition when assessing that such interventions are meaningful and successful. The aim of this thesis is to study markers of general stress as indicators of changes in the risk of negative health effects, which are feasible when evaluating interventions at group as well as at individual level. Sleep disorders are common in conjunction with stress, and are also associated with negative health effects. Sleep has been investigated in this thesis using: (1) a questionnaire assessing global sleep (during the last six months) (studies I and II); (2) self-reported sleep during one or several specific nights of interest (in a sleep diary) (studies III and IV); (3) objectively measured sleep with an actigraph (study IV). Heart rate variability during sleep is another potential marker, and is examined in study III. Study I and study II are five-year prospective studies investigating sleep as a predictor of: (I) sickness absence in three groups with different pain conditions, and (II) change in number of pain sites between baseline and follow-up. Study III is a cross-sectional twin study investigating self-reported stress during the day and changes in heart rate variability, heart rate and self-reported sleep quality the subsequent night. Further, study III investigated whether individual factors related to genes and/or familial environment had an effect on the associations between stress and heart rate variability/heart rate and stress and self-reported sleep quality. In study IV, repeated objective and subjective sleep measurements during seven consecutive nights were performed. The measurements took place in a workplace, i.e., under conditions translatable to an OHS setting. The number of consecutive measurements that are needed for a reliable sleep measure, and the correlation between subjective and objective sleep measures, are investigated in this study.

Sleep disturbances were found to be an indicator of increased risk of sickness absence during five-year follow-up within all the three pain groups that presumably represent three different levels of wellbeing at baseline (study I). Further, sleep was an indicator of change in number of self-reported pain sites between baseline and the five-year follow-up. Associations between perceived daytime stress and changes in heart rate variability, heart rate, and self-reported sleep quality the subsequent night were seen in study III. The results of study III further indicate that these associations are influenced by individual factors related to genes and/or the familial environment. In study IV, it was shown that subjective (sleep quality) and objective (sleep efficiency) measures correlate poorly on a day-by-day basis, which indicates that objective and subjective sleep may capture different dimensions of sleep. If only week nights are included in repeated sleep measurements, fewer measurements are needed to obtain a reliable measure of sleep as compared with when weekend nights are included. In all, measurements of sleep are easier to use than measurements of heart rate variability, which makes sleep a more realistic marker, especially when considering larger groups.

List of scientific papers

I. Aili K, Nyman T, Hillert L, Svartengren M. Sleep disturbances predict future sickness absence among individuals with lower back or neck-shoulder pain: A 5-year prospective study. Scand J Public Health, 2015, 43: 315-323.
https://doi.org/10.1177/1403494814567755

II. Aili K, Nyman T, Svartengren M, Hillert L. Sleep as a predictive factor for the onset and resolution of multi-site pain: A 5-year prospective study. Eur J Pain, 2015, 19: 341-349.
https://doi.org/10.1002/ejp.552

III. Aili K, Hillert L, Balliu N, Anderson M, Bogo R, Skjönsberg Å, Svartengren M. Genetic and early environmental factors influence markers of stress. [Submitted]

IV. Aili K, Åström-Paulsson S, Stoetzer U, Svartengren M, Hillert L. Reliability of objective and subjective sleep measurements in adults: the design of sleep assessments. [Submitted]