Stressful life experiences among women are not associated with a greater likelihood of developing multiple sclerosis, researchers found.
In two large U.S. studies of female nurses, neither childhood physical and sexual trauma nor adult stress were related to the chances of developing the disease, Trond Riise, PhD, of the University of Bergen in Norway, and colleagues reported in the May 31 issue of Neurology.
But, they wrote, although the findings do not support a relationship between stress and the development of multiple sclerosis, "future studies with more focused and frequently measured stress assessments are needed to preclude a firm exclusion of stress as a potential risk factor for MS."Action Points
- Note that researchers compared results from two large, long term observational studies and found no link between stress and multiple sclerosis.
Several previous studies have identified a link between stressful life events and exacerbations of multiple sclerosis, with proposed mechanisms involving the glucocorticoid and beta-adrenergic pathways. But it had remained unclear whether stress was related to the chances of developing the disease in the first place.
Riise and his colleagues used two large cohorts of female nurses -- the Nurses' Health Study and the Nurses' Health Study II -- to explore the issue.
The first study was established in 1976 and enrolled 121,700 women ages 30 to 55. The second was established in 1989 and enrolled 116,671 women ages 25 to 42.
In the Nurses' Health Study, information on general stress at home and at work was collected via questionnaires administered in 1982.
In the Nurses' Health Study II, information on physical and sexual abuse in childhood and adolescence was collected in 2001.
"Such traumas can fundamentally alter systems that mediate the effect of stress (e.g., sensitization of neuroendocrine response), reduce neuroendocrine regulation of inflammation (e.g., glucocorticoid resistance), and increase inflammatory activity," the authors wrote. "These effects can extend into adulthood, suggesting that these systems are permanently altered by childhood trauma."
In both studies, women self-reported multiple sclerosis, which was then verified by their neurologists.
Overall, there were 77 women in the Nurses' Health Study who developed multiple sclerosis after the start of the study and had information available on stress.
There were 292 women in the Nurses' Health Study II who had information on childhood trauma and stress and who reported having multiple sclerosis. The number was higher in the second study because it included all prevalent cases and the women were younger at baseline.
After adjusting for age, ethnicity, latitude of birth, body mass index at age 18, and smoking, the risk of developing multiple sclerosis was not associated with any level of stress in the home or at work. For example, the hazard ratio for multiple sclerosis associated with severe home stress was 0.85 (95% CI 0.32 to 2.26).
Similarly, there was no increased risk of multiple sclerosis associated with either physical or sexual abuse during childhood or adolescence.
"It could be that few traumatized individuals who had substantial negative health consequences from childhood abuse were in the study population, given the demanding nature of the nursing profession," the authors speculated.
Riise and colleagues noted that a major challenge in assessing the relationship between stress and the development of multiple sclerosis -- if, in fact, one exists -- is getting an unbiased measurement of stress.
"A prospective design can overcome biases related to the effects of MS symptoms on self-reported stress," they wrote. "However, because the disease is infrequent, initiating a prospective study specifically with this aim is not feasible."
The study was funded by the National Institite of Neurological Disorders and Stroke.
Riise reported receiving funding for a one-year research visit at the Harvard School of Public Health from the Norwegian Research Council. His co-authors reported relationships with the the National Institutes of Health, the U.S. Department of Veterans Affairs/Health Services Research & Development, the Consortium of MS Centers, the National Multiple Sclerosis Society, the Society for Epidemiologic Research Developmental Origins of Health and Disease, Social Science & Medicine, the American Journal of Epidemiology, the Michael J. Fox Foundation, Neurology, Annals of Neurology, Merck Serono, and the U.S. Department of Defense.
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