An Epidemiological Study of Exhaustion in the Context of Chronic stress. Concept, Cortisol, Causes and Consequences

Sammanfattning: The interest in exhaustion has increased rapidly during the last few decades in many developed countries. In Sweden, prevalence of exhaustion increased by 50 percent on average between 1989 and 2005, and recent data reveals that exhaustion still remains at this higher level. Scientifically, exhaustion is not clearly defined. Chronic stress is acknowledged to give rise to exhaustion, but specific mechanisms involved have generally been overlooked in stress research. The relatively new concept of “hypocortisolism” in this context, referring to low levels of circulating cortisol, and observed in disorders featuring exhaustion, should be of interest. Hypocortisolism has also been suggested to comprise a mechanism for development of stress-related disease that challenges the previous general view of stress pathophysiology. The main objective of this thesis was to evaluate whether exhaustion as concept may be helpful in elucidating stress mechanisms. The four included Papers explored the discriminant validity of exhaustion in relation to depression and anxiety; HPA activity in exhaustion; associations with psychosocial work stressors; and significance for onset of a “stress-related disease”, i.e. cardiac disease. Two study populations were used. For Papers I, III, and IV, analyses were performed on data from the Malmö Shoulder and Neck Study (N = 12,607); prospective data on coronary heart disease for Paper IV was obtained through data linkage. For Paper II, a working population sample (N = 78) was analysed. Exhaustion was assessed by means of the (inverted) SF-36 vitality measure. In Paper I, exhaustion emerged separately from depression and anxiety in factor analysis, supporting the conceptual integrity of exhaustion. In Paper II, HPA dysregulation in terms of a flattened diurnal cortisol rhythm (due to lower morning cortisol) was found in exhaustion. In Paper III, relationships with work-related stressors were demonstrated. Finally, in Paper IV, the contribution of exhaustion, independent from depression and anxiety, in development of coronary heart disease was indicated in men. The findings point to a unique and potentially important role of exhaustion in stress theory. It may, however, be important to focus gender in search of relevant concepts and mechanisms for development of stress-related disease. The search for preventive measures should be essential in future research.