"The women were interviewed about their MS symptoms during each trimester of their pregnancies and then about their breastfeeding and menstruation history every few months in the 12 months after they gave birth.
The women with MS were more likely not to breastfeed and to begin supplemental formula feeding during their baby's first two months of life compared to the healthy women, the researchers found.
Of the 52 per cent of women with MS who did not breastfeed or who began regular supplemental feedings, 87 per cent had a relapse within a year of their babies' births. That compared to just 36 per cent of the women with MS who breastfed exclusively for at least two months.
The researchers note that the mothers who breastfed exclusively had significantly prolonged "lactational amenorrhea" (absence of a period), which seemed to be linked to a decreased risk of relapse in MS.
When the researchers asked the mothers with MS why some chose not to breastfeed exclusively, the women reported that their primary reason was so that they could begin taking their MS medications again. The medications, including interferon beta and natalizumab, work by modifying the immune system and are not recommended for use during pregnancy or breastfeeding.
The results of this study suggest that women with MS should be encouraged to breastfeed exclusively for at least the first two months instead of resuming medications, the authors conclude.
"Our findings call into question the benefit of foregoing breastfeeding to start MS therapies," they write, adding that larger studies are needed to confirm the findings.
The researchers say they aren't sure why breastfeeding might be beneficial to women with autoimmune diseases such as MS.
"Studies of immunity and breastfeeding, while plentiful, are predominantly focused on breast milk content and health benefits to the infant. Little is known about maternal immunity during breastfeeding."