Having a stressful home or work environment doesn't make a person more likely to develop multiple sclerosis, hints a large new study.
Previous research has suggested that in people who already have the chronic disease — which affects the brain and spinal cord — stressful events make flare-ups more likely. In the new study, the authors looked at whether stress raised a woman's risk of getting the disease, and couldn't find a link.
Despite studying more than 150,000 women, though, the researchers said they couldn't rule out a connection either because they couldn't account for all stressful life events and their impact on the body's disease-fighting systems.
"These results do not support a major role of stress in the development of the disease, but repeated and more focused measures of stress are needed to firmly exclude stress as a potential risk factor for MS," they report today in the journal Neurology.
The National Multiple Sclerosis Society estimates that about 400,000 people in the U.S. have MS. There is no cure for the disease, which occurs when the protective coating around nerve fibers begins to break down -- slowing the brain's communication to the rest of the body.
Symptoms include fatigue and problems with balance and muscle coordination, as well as memory loss and trouble with logical thinking in some people.
To determine if stress is linked to the onset of MS, researchers including Harvard Medical School's Dr. Alberto Ascherio analyzed data from two large nationwide studies of female nurses.
Starting in 1976 for one study and 1989 for the other, women were regularly asked about any new diseases they were diagnosed with, including MS, and diagnoses were confirmed by their doctors.
The first group of about 93,000 nurses was also given a questionnaire about their levels of stress at home and at work, six years after the study began. The second group of about 68,500 nurses filled out questionnaires about physical and sexual abuse during childhood and adolescence —another possible cause of stress.
As of 2004 to 2005, 77 women in the first group and 292 in the second had been diagnosed with MS and responded to questionnaires about stress. The number in the second study was higher because researchers included women who had been diagnosed with MS before the study was initiated, and that group was younger.
MS is typically diagnosed between the ages of 20 and 40.
How much stress women reported both at home and work was not linked with their chance of having MS. For example, 44 percent of all women said in their questionnaire that they experienced moderate stress at work, compared to 39 percent of women with MS. Those numbers were similar for moderate stress at home.
Severe stress at work was reported by 11 percent of all women and 5 percent of the MS group in particular.
Nor did a history of physical abuse make women any more likely to get MS.
The researchers found a slight increase in MS in women who said they were touched multiple times in a sexual way as a child — but they note that result is hard to interpret, especially because women who said they were touched once seemed to have a lowest risk of MS.
One limitation of the study was that it only included female nurses, so the findings may not apply to men, the authors say.
Another limitation was that the study only asked about stress at a single time point.
Dr. Thomas Mack, who studies MS at the University of Southern California, said that one question when considering stress is whether to ask people how they feel or to measure the body's stress response.
"The main difficulty in studying stress specifically is, what does the word mean?" said Mack, who was not involved in the current study.
"Does it have a specific physiologic meaning, or is it a very general term? Some people feel more stressed than others — whether there's any physiologic meaning to that is very difficult to know," he told Reuters Health.
Researchers sometimes measure stress by looking at the presence of certain hormones in the blood.
Mack said this issue of stress as a possible cause of MS hasn't been studied much — mostly because doctors who treat MS are more interested in what causes exacerbations in their patients than why they developed the disease in the first place.