Women with multiple sclerosis often find that their symptoms ease during pregnancy. And the evidence is growing that breastfeeding might have a similar benefit.
A new review of 16 studies found that overall, women with MS who breastfed were 37% less likely to have a relapse within a year of giving birth, versus those who bottle-fed.
The findings do not prove breastfeeding is protective, experts said.
But the evidence of that possibility is getting stronger, said Dr. Kristen Krysko, lead researcher on the review and a neurology fellow at the University of California, San Francisco.
Recent studies on the question, she said, have been better designed than some earlier ones - accounting for several alternative explanations for the link between breastfeeding and lower relapse risk.
And overall, they point to a protective effect, Krysko said.
In the United States alone, nearly 1 million people are living with MS, according to the National MS Society. It's two to three times more common among women than men, and usually arises during the childbearing years.
MS is a neurological disorder caused by a misguided immune system attack on the body's own myelin - the protective sheath around nerve fibers in the spine and brain. Depending on where the damage occurs, symptoms include vision problems, muscle weakness, numbness and difficulty with balance and coordination.
Most people with MS have the relapsing-remitting form, meaning their symptoms come in waves, with symptom-free periods in between. Research over the years has shown that many women see fewer symptom relapses during pregnancy - possibly because the immune system dials down to protect the fetus.
After giving birth, some women see their symptoms flare. But whether breastfeeding can help limit that risk remains unclear.
For the new analysis, Krysko's team pooled the results of 16 studies that compared women with MS who breastfed with those who did not - following them for anywhere from three to 12 months after giving birth.
On average, women who breastfed were 37% less likely to have a relapse. When the researchers zeroed in on four recent, higher-quality studies, the risk reduction was a little bigger - 43%.
Still, questions remain, Krysko said.
One issue is that women with MS who choose to breastfeed may be quite different from those who did not: A woman whose disease was very active before pregnancy might decide not to breastfeed so that she can restart her MS medication. (None of the so-called disease-modifying drugs for MS are approved for use in pregnancy, and it's not known if they can be safely used during breastfeeding, according to the National MS Society.)
The better-quality studies in the review accounted for women's prior disease activity, Krysko said. But that's still not definitive proof that breastfeeding is directly protective.
It's also unclear, Krysko said, how a woman's experience during pregnancy fits in: If she has a relapse while she's pregnant, does that affect the odds of getting any benefit from breastfeeding?
The findings were published Dec. 9 in the journal JAMA Neurology.
Kathleen Costello is associate vice president for healthcare access at the National MS Society. She called the findings "important," but also stressed they do not prove breastfeeding prevents relapses.
"It's important to have this information, but what's driving this association?" said Costello, who wasn't involved with the study.
According to Krysko and colleagues, breastfeeding might be protective because of the hormonal changes that come with it. But that's just a theory.
"The benefits of breastfeeding for mother and baby - outside of MS - are well-established," Costello said. And the evidence, at least, suggests that breastfeeding does not increase the risk of relapse soon after pregnancy, she noted.
That said, MS is "very individual and heterogeneous," Costello pointed out. So she recommended that women planning a pregnancy talk with their doctors about how they will manage their MS during and after.
Krysko agreed. "There's still a high risk of postpartum relapses even if breastfeeding, so it's important [for women] to discuss with their neurologist the best postpartum management strategy for them, which may depend on their prior MS disease activity."
Sources: Kristen Krysko, M.D., clinical fellow, neurology, University of California, San Francisco; Kathleen Costello, M.S., C.R.N.P., M.S.C.N., associate vice president, healthcare access, National MS Society, New York City; Dec. 9, 2019, JAMA Neurology, online.