Researchers have found new links between stress at work and risk of rheumatoid arthritis. It seems that low levels of job-related control may increase the risk, but high demands may actually be protective.
A team led by Dr. Camilla Bengtsson at the Karolinska Institute in Sweden used figures on 1,221 rheumatoid arthritis patients aged 18 to 65 years, and 1,454 similar healthy people.
Psychological job demands and job “decision latitude,” or personal control, were measured by questionnaire. Participants facing high demands with low control were defined as experiencing “job strain” as opposed to relaxed working conditions.
Earlier work has linked job strain with an increased risk of several diseases, including heart disease, because of a possible association with inflammation. But it has not previously been studied in relation to rheumatoid arthritis.
The team explains, “Data on environmental factors that may cause rheumatoid arthritis is scarce.” Results of their new study appear in the journal Psychotherapy and Psychosomatics.
Low decision latitude was linked to a 60 percent increase in risk of rheumatoid arthritis, but surprisingly, high psychological job demands were linked to a 20 percent lower risk. Job strain, a combination of the two, was linked with a 30 percent higher risk, compared with relaxed working conditions.
The team concludes, “The main new finding of this study was that low decision latitude was associated with an increased risk of developing rheumatoid arthritis. Furthermore, some evidence that those with high psychological job demands had a decreased risk of rheumatoid arthritis was found.”
Dr. Maurizio Cutolo of the University of Genoa, Italy, has looked into this link. He writes, “Stress is now recognized as an important risk factor in the pathogenesis of rheumatoid arthritis.”
He believes the mechanism can be explained by brain activity. “Activation of the stress response system influences the relationships between the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system and the immune system,” he writes.
“The stress response results in the release of neurotransmitters (norepinephrine), hormones (cortisol) and immune cells. Major life events lead to an intense release of stress mediators, whereas in minor life events, only short-lived surges of neurotransmitters and hormones are expected.”
Long-lasting stress may lead to proinflammatory effects, because no adequate long-term anti-inflammatory responses are available, he states.
The Swedish team also investigated the possible influence of formal education and occupational class on risk of rheumatoid arthritis. Using figures on 930 rheumatoid arthritis patients and 1,126 similar healthy people, they calculated the risk of developing rheumatoid arthritis for different levels of formal education and occupational classes.
Those without a university degree had a 40 percent increased risk, compared with those with a university degree. Manual employees, and assistant and intermediate non-manual employees had a 20 percent higher risk than higher-ranking non-manual employees.
The researchers say that these increased risks were mainly confined to women, who constitute three times as many sufferers as men. They suggest that “as yet unexplained environmental or lifestyle factors, or both, influence the risk of rheumatoid arthritis, even in the relatively egalitarian Swedish society.”
In contrast to osteoarthritis, the more common form of arthritis caused by trauma or infection of a joint, rheumatoid arthritis is an autoimmune disease in which the body attacks itself.
Dr. Bengtsson believes that environmental factors are important, as the shared risk among identical twins is low, at only 12 to 15 percent. Evidence of the role of social class is crucial for understanding its causes, she writes. A limited formal education has been found to raise the risk of rheumatoid arthritis, but results are “somewhat inconsistent.” She thinks this inconsistency may be due to low participant numbers or the inclusion of other types of arthritis.
Because Sweden provides universal access to medical care, Dr. Bengtsson says it is unlikely that the links she found can be due to variation in treatment.
“Taking these considerations into account, the results from our study add to the likelihood that socioeconomic status indeed influences the risk of developing this disease even today, and even in Western Europe, including the highly egalitarian societies in Scandinavia,” she says.
“The lower risk in individuals with high education and less manual work may reflect fundamental factors that may have changed the overall pattern of rheumatoid arthritis in many Western societies toward a lower overall rate and a higher age of diagnosis,” she suggests.
Bengtsson, C. et al. Psychosocial Stress at Work and the Risk of Developing Rheumatoid Arthritis: Results from the Swedish EIRA Study. Psychotherapy and Psychosomatics, Vol. 78, April 2009, pp. 193-94.
Bengtsson, C. et al. Socioeconomic status and the risk of developing rheumatoid arthritis: results from the Swedish EIRA study. Annals of the Rheumatic Diseases, Vol. 64, November 2005, pp. 1588-94.
Cutolo, M. and Straub, R. H. Stress as a risk factor in the pathogenesis of rheumatoid arthritis. Neuroimmunomodulation, Vol. 13, 2006, pp. 277-82.