An international research team reports that a common gut microbe might curb the risk in women of developing multiple sclerosis. The scientists, from Australia and the Netherlands, published their study (“Helicobacter pylori infection as a protective factor against multiple sclerosis risk in females”) online in the Journal of Neurology Neurosurgery & Psychiatry.

“Our results could reflect a protective role of H. pylori in the disease development. However, it may be that H. pylori infection is a surrogate marker for the ‘hygiene hypothesis,’ a theory which postulates that early life infections are essential to prime the immune system and thus prevent allergic and autoimmune conditions later in life,” wrote the investigators. “The fact that the association between H. pylori seropositivity and MS risk was seen almost exclusively in females requires further investigation.”

The prevalence of multiple sclerosis (MS) has increased worldwide, in tandem with other autoimmune diseases, but the reasons behind this rise are unclear. Some studies have suggested a link between early childhood infection and reduced MS risk, but they have all been small.

The researchers tested 550 people with confirmed MS and a comparison group of 299 healthy people, matched for age and sex, for the presence of antibodies to Helicobacter pylori. The tests were done between 2007 and 2011.

H. pylori is usually acquired before the age of 2, and lasts for life in the stomach, unless treated. Around half the world's population is infected with it, most of whom live in the developing world, where hygiene standards and antibiotic prescribing rates tend to be lower than they are in developed countries.

The results showed that the prevalence of the infection was significantly lower in those with MS than in the comparison group, but only among women, in whom it was around 30% lower. Furthermore, after taking account of influential factors, such as age at diagnosis, year of birth, and duration of symptoms, those women with MS who tested positive for H. pylori seemed to be less disabled by their condition than those who tested negative for the infection.

The reverse was true in men, among whom a positive test result was linked to higher rates of disability.

There was no evidence of any link between the presence of the infection and relapse rate. There's no obvious explanation for the gender disparity. Rates of MS are higher in women than they are in men, with most of the increased prevalence of MS in recent years, occurring in women.

In an editorial in the journal, Jun-ichi Kira, M.D., Ph.D., of the Neurological Institute at Kyushu University in Japan, points out that the lower disability scores reported by the women with MS who tested positive for H. pylori suggests that the infection might be protective.

“Collectively, such an inverse correlation of H. pylori infection with MS in developing countries where MS and allergic disorders have increased, may support the 'hygiene hypothesis,'” he points out. “Although why the protective effects of H. pylori against MS were observed only in women remains to be elucidated, but might explain the recent increase in female to male ratio of MS in developed countries.”