Multiple sclerosis (MS) is a disease in which the insulating covers of nerve cells in the brain and spinal cord are damaged by the body's immune system.
"This is another example of a benefit to the mother from breastfeeding," said Annette Langer-Gould from health care company Kaiser Permanente Southern California in the US.
"Other health benefits include a reduced risk of breast cancer, ovarian cancer, type 2 diabetes and heart attack," said Langer-Gould.
Women with MS have significantly fewer relapses, or attacks, during pregnancy or while they are breastfeeding exclusively, meaning that the child receives only breast milk.
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The study involved 397 women with an average age of 37 who were newly diagnosed with MS or its precursor, clinically isolated syndrome. They were compared to 433 women matched for race and age.
The women were given in-person questionnaires about pregnancies, breastfeeding, hormonal contraceptive use and other factors.
A total of 85 of the healthy women had breastfed for 15 months or more, compared to 44 of the women with MS. For the healthy women, 110 breastfed for zero to four months, compared to 118 of the women with MS.
Women who were age 15 or older at the time of their first menstrual cycle were 44 per cent less likely to develop MS later than women who were 11 years old or younger at the time of their first menstruation. A total of 44 of the healthy women were 15 or older at first menstruation, compared to 27 of the women with MS. Additionally, 120 of the healthy women were 11 years old or younger at first menstruation, compared to 131 of the women with MS.
"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," she said.
The study was published in the journal Neurology.