Previously stress has been described as a rather uniform entity in all individuals, with more or less consistent symptoms, but this study shows that dominant stress symptoms in middle age may vary between persons. The study involved more than 5,000 persons who were followed up for almost thirty years from working age to old age.

"We were able to identify four different stress profiles among occupationally active persons aged from 44 to 58 years: negative reactions to work and depressiveness; perceived decrease in cognition; sleep disturbances; and somatic symptoms. Some people suffered from occasional symptoms, but in some cases these symptoms were observed in several time points and thus were considered as continuous," says Dr. Jenni Kulmala.

All kinds of stress symptoms in midlife correlated with disability 28 years later. Persons who had reported long-term stress symptoms in midlife had more difficulties in the basic activities of daily living, such as bathing and dressing, and also in more demanding instrumental daily activities, such as shopping, coping with light housework, handling financial matters, taking medication and using the telephone at the mean age of 78 years. Additionally, the risk for inability to walk two kilometres was 2-3 times higher for those with constant stress symptoms in midlife. Occasional stress symptoms in midlife also increased the severity of disability, but less than constant symptoms.

"Stress symptoms are associated with chronic conditions and a maladaptive lifestyle, which may partly explain the found association. However, in our study, the association was not completely explained by such mediators. Therefore, it is also possible that the chronic activation of stress responses may result in the "wear and tear" of the human body and thus increase the risk of old age disability," says Dr. Kulmala.

The results obtained in this study offer targets for interventions aimed at preventing the decline of physical functioning, and promoting healthy aging.