Women who breastfed for 15 months were less at risk of developing MS. iStock

Mothers who breastfeed for longer may have a lower risk of developing multiple sclerosis afterwards, scientists have shown. These benefits are seen when they breastfeed for 15 months or more.

Multiple sclerosis (MS) is a chronic autoimmune disease. This means that the immune system turns against the body, in this case attacking the myelin sheath that surrounds the brain and the spinal cord.

It is thought that reproductive factors can play a role in the way the disease evolves over time. A number of recent studies have shown that the levels of sex hormones and the use of oral contraceptives can influence women's risk of developing the disease.

MS has been shown to affect mostly women during their childbearing years - it is rare that it develops before puberty or after menopause. Furthermore, women with MS are less likely to relapse during pregnancy or while they breastfeed.

"Many experts have suggested that the levels of sex hormones are responsible for these findings, but we hypothesised that the lack of ovulation may play a role, so we wanted to see if having a longer time of breastfeeding or fewer total years when a woman is ovulating could be associated with the risk of MS," said Annette Langer-Gould, member of the American Academy of Neurology, in a statement.

Research into the effects of breastfeeding has been particularly interesting to scientists because it is an easily modifiable factor, with other reported maternal health benefits.

In a study now published in the journal Neurology, Langer-Gould and colleagues have investigated whether breastfeeding could not only prevent MS relapse, but also reduce mothers' risk of developing MS for those women who have never been diagnosed with the disease.

The scientists recruited 397 women with an average age of 37 for their study. They had been newly diagnosed with MS or its precursor, clinically isolated syndrome. They were compared to 433 women matched for race and age. All the participants filled in questionnaires regarding pregnancies, breastfeeding, hormonal contraceptive use and other reproductive factors (including the age they first got their periods or any absence of menstruation at some point in their lives).

The researchers analyse the collected data and discovered that women who had breastfed for a cumulative amount with one or more children for 15 months or more were 53% less likely to develop MS compared with women breastfed for four months or less in total.

"This study provides more evidence that women who are able to breastfeed their infants should be supported in doing so," Langer-Gould said. "Among the many other benefits to the mother and the baby, breastfeeding may reduce the mother's future risk of developing MS."

They also identified a connection between age at menstruation and risk of developing MS. Indeed, they found that women who were age 15 or older at the time of their first menstrual cycle were 44% less likely to develop MS later than women who were 11 years old or younger at the time of their first menstruation.

The study only shows an association, it does not prove that breastfeeding prevents MS. Other limitations include the fact that women were asked to remember information from many years before so they may not have remembered everything correctly and the fact the scientists did not investigate women's reasons for not breastfeeding or breastfeeding only for a short period of time.

"The majority of the 100,000 people living with MS in the UK are women. Many are diagnosed in their twenties and thirties, at a time when they may be thinking about starting a family," Dr David Schley, Research Communications Manager at the MS Society, told IBTimes UK.

"We know that pregnancy can have a positive effect for women with MS and that there are recognised benefits of breastfeeding. But after looking at this study, we don't think there's enough evidence to encourage women to breastfeed just because they're concerned about developing MS."