If you’re among the estimated one-third of people with multiple sclerosis who take omega-3 fatty-acid supplements (such as fish oil) to slow the disease’s progress, you may be disappointed in the findings of a study published Monday afternoon.

Reporting in the journal Archives of Neurology, researchers in Norway ran a randomized controlled trial involving just under 100 MS patients. For the first six months, one group (46 people) received omega-3 supplements; the other 46 people received placebo. After six months, all participants also were given interferon beta-1a — the disease-modifying drug available in the United States as Avonex — for an additional 18 months.

MS is an unpredictable, chronic autoimmune condition affecting the central nervous system; in people with MS, immune-system cells attack the protective sheath lining nerves in the brain and spinal cord. That damage shows up on MRI scans as lesions.

There is no known cure for MS, but a growing number of medications are available to slow its progression and help prevent lesions from forming. But those medications don’t work equally well for all patients, and some people experience bothersome side effects. Many people with MS seek complementary and alternative treatments, including the use of omega-3 supplements; those could potentially ease the inflammation that’s characteristic of the disease.

But this study found no statistically significant difference in the number of lesions the two groups developed, either during the initial six-month period nor during the following 18 months, when both groups were taking interferon beta-1a. Both groups did show reduced disease activity once the interferon beta-1a was introduced.

Two earlier studies had found some evidence that omega-3 supplementation might indeed do some good in keeping MS damage in check. But as this new study notes, those studies, unlike the new research, did not use MRI imaging to document disease progression. The authors note that MRI can detect tissue damage long before that damage causes any noticeable clinical symptoms.

The authors add that omega-3 fatty acids did not appear to cause any harm to the MS patients who took them; nor did those supplements appear to interfere with the interferon beta-1a treatment.