Exercise Not Protective Against MS Development in Women

Deborah Brauser

October 04, 2016

Although exercise has been shown to improve symptoms after the onset of multiple sclerosis (MS), new research suggests that it does not protect against the development of the disease.

After reviewing records for more than 193,000 participants in the Nurses' Health Study (NHS) and NHS II, investigators found a trend toward a reduced rate of MS in the women with the highest levels of physical activity at baseline compared with those with the lowest levels of activity, but the association was not significant.

Interestingly, this trend may have been caused in part by the women later diagnosed with MS reducing their level of exercise in response to already having subclinical MS, report the investigators, led by Kirsten S. Dorans, ScD, Harvard T.H. Chan School of Public Health and Beth Israel Deaconess Medical Center, Boston, Massachusetts.

"Prior to onset of MS, women were already changing their physical activity behavior in response to something going on in their lives and in their bodies," principal investigator Kassandra L. Munger, ScD, research scientist at the Harvard T.H. Chan School of Public Health, told Medscape Medical News.

"There also weren't consistent associations between physical activity in early life and future MS risk. Again, this suggested that what we were picking up was probably not a biological association but more likely explained by women changing their activity early in the disease process," said Dr Munger.

The findings were published online September 28 in Neurology.

27% Reduced MS Rate

The investigators assessed records for 81,723 women who took part in the first NHS study between 1986 and 2004 and 111,804 who took part in the NHS II between 1989 and 2009.

Using information on physical activity reported at baseline and in follow-up questionnaires, "we calculated total metabolic equivalent hours of physical activity per week, a measure of energy expenditure," report the researchers.

The participants also disclosed information on early-life activity. Those who received a new diagnosis of MS reported on their diagnosis and on related symptoms in every-other-year questionnaires. Once a patient with MS granted permission, the medical records were reviewed by a study neurologist.

Women in the NHS were followed for an average of 16.7 years and women in the NHS II were followed for an average of 18.2 years. After baseline, there were 341 total cases of MS during follow-up.

The participants in the highest quartile of baseline physical activity quartile had a 27% reduced rate of MS vs those in the lowest quartile, a trend that was not statistically significant (relative rate [RR], 0.73; 95% confidence interval [CI], 0.55 - 0.98; P for trend = .08).

Six-year "lagged analyses" showed that there was no longer a trend for this association, "suggesting lower physical activity could have been an early sign, rather than the cause, of MS," write the investigators.

There was no association at all between MS and moderate physical activity at baseline.

The authors noted a significant trend for decreased MS development "with increasing number of months of strenuous activity" that occurred when the participants of both cohorts together were between the ages of 18 and 22 years (P for trend = .01).

However, when just the NHS II was examined for strenuous activity between the ages of 12 and 22 years, there were no associations between MS reduction and activity during any of the age subgroups, including between 18 and 22 years.

Finally, women with MS decreased their physical activity over time compared with those without MS, and this decrease occurred up to 6 years before they experienced first MS symptoms.

"In this large prospective study with validated measures of physical activity, we found weak and nonconvincing evidence that higher physical activity reduces the risk of incident MS," summarize the researchers.

"This means we need to keep exploring and looking into other areas for modifiable risk factors," added Dr Munger. "And of course, physical activity should still be promoted for overall health."

Exercise Still "Extremely Important"

Invited to comment, Lauren Krupp, MD, director of NYU Langone's Multiple Sclerosis Comprehensive Care Center, said in a statement sent to Medscape Medical News that although exercise has been shown to play an important part in preventing certain cardiac and vascular disorders, its role is a little different when it comes to MS.

Still, "exercise is extremely important in managing MS symptoms," said Dr Krupp.

She noted that past research has suggested an association between increased risk for MS and low vitamin D levels, low sun exposure in childhood and adolescence, a history of mumps, or childhood obesity. So, it was "very logical" for the investigators to assess whether a history of low physical activity was also a risk factor for the disease.

"What we know…is that it's very important for people with MS to exercise, since it reduces symptoms like fatigue, improves strength and endurance, and has positive effects on outlook," said Dr Krupp, adding that an important question has been whether lack of exercise could be a trigger for the disease.

The current study's results answer that question. "But once the diagnosis of MS was made, over time the nurses seemed to exercise less than those individuals who didn't have MS."

Although lack of exercise is not a trigger for MS, Dr Krupp added that staff at her MS center will continue to promote exercise, as well as mindfulness and yoga, "as part of the multidisciplinary treatment approach we advocate."

The study was supported by grants from the National Institutes of Health. Dr Munger reports having received a research grant from the National MS Society. Disclosures for the coauthors are in the paper.

Neurology. Published online September 28, 2016. Abstract

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