By Steven Reinberg
HealthDay Reporter Tue Sep 13, 7:02 PM ET

TUESDAY, Sept. 13 (HealthDayNews) -- Women who take oral contraceptives or are pregnant have a lower risk of developing multiple sclerosis, a new study finds.

Earlier research with animals had shown that the female hormone estrogen delayed the onset and eased the course of MS. This suggested that oral contraceptives, which contain estrogen, and conditions associated with hormonal changes, such as pregnancy and the postpartum period afterward, may affect the risk of developing the disease, the researchers said.

"MS is more frequent in women than men," said study author Dr. Alvaro Alonso, a research fellow at the Harvard School of Public Health. "Some people have thought that perhaps estrogen can be modifying the risk of MS."

To explore the possible link between estrogen and multiple sclerosis, Alonso's team compared oral contraceptive use among 106 women who had been diagnosed with MS between Jan. 1, 1993, and Dec. 31, 2000, with 1,001 women without the disease.

The researchers found the incidence of multiple sclerosis among women using oral contraceptives was 40 percent lower. In addition, women had a higher risk of developing MS during the six months following a pregnancy and a slightly lower risk during pregnancy, the researchers noted.

Estrogen has an effect on the immune system, and MS is caused by an alteration in the immune system, Alonso explained. "We have seen that oral contraceptives can reduce the risk of MS in the short term," he said. "If you are taking oral contraceptives and you are [destined] to have MS, the onset of MS can be delayed one to two years."

In addition, when women are pregnant they have a lower risk of developing MS, Alonso said. "But this risk increases in the postpartum period, in just the six months after the delivery," he said.

The findings appear in the September issue of the Archives of Neurology.

Multiple sclerosis is believed to be an autoimmune disease that affects the central nervous system, which includes the brain, spinal cord, and optic nerves. Nerve fibers of the central nervous system are protected by a fatty tissue called myelin, which helps fibers conduct electrical impulses.

In MS, myelin is lost, leaving scar tissue called sclerosis. This disrupts the nerves' ability to conduct electrical impulses, resulting in symptoms that can include vision problems, loss of balance, lack of muscle coordination, slurred speech, and tremors, according to the National Multiple Sclerosis Society.

Alonso doesn't see the findings having any immediate implications for treating or preventing MS. "The decision to take oral contraceptives or the decision to become pregnant must not be influenced by the idea that this can increase or decrease the risk of MS," he said.

One expert noted that the findings may add to the understanding of why MS is more prevalent among women.

"There is a strong relationship between gender and immune-mediated disorders, such as MS, lupus, rheumatoid arthritis and others," said Nicholas LaRocca, director of health-care delivery and policy research at the National Multiple Sclerosis Society.

Moreover, several studies have found a relationship between pregnancy and reduced risk of MS attacks, he said. "So, this study adds one more bit of evidence to suggest that there may be significant hormone-mediated factors at work in MS."

Exactly what these factors are, how they work, and what their implications may be for future treatments remain to be determined, LaRocca added. "The society has for several years mounted an ambitious program of research directed at understanding the significance of gender in the pathogenesis of MS. As we continue to learn more about this aspect of MS, it will add to our understanding of the disease and, it is hoped, how best to treat it," he said.

Another study published in the same issue of the journal uncovers some new facts about a common MS treatment.

While treatment with the protein interferon seems to reduce new areas of damage in the brains of MS patients, it doesn't appear to affect the duration of these damaged regions, researchers reported.

Dr. Francesca Bagnato, of the National Institute of Neurological Disorders and Stroke, and colleagues analyzed MRIs for both the formation and duration of these damaged areas, called black holes, in six patients with relapsing-remitting type MS.

Bagnato's team found that the creation of new black holes increased during both interferon treatment and no treatment. But fewer were created during treatment.

"One can postulate that although interferon may reduce the frequency of black holes, after the lesion occurs, the drug is not changing the pathological process," Bagnato's group concluded.

More information

To learn more about the disease, visit the National Multiple Sclerosis Society.

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