It’s long been known that breastfeeding prevents SIDS, though in what way and to what degree remains disputed. Now, a new study has quantified how long to breastfeed in order to reap these specific protective benefits for infants: Breastfeeding for at least two months has been associated with cutting babies’ risk of Sudden Infant Death Syndrome in half.

Additionally, researchers found that mothers do not need to breastfeed exclusively for their baby to get the benefits; partial breastfeeding for two months yielded the same protection against SIDS — potentially good news for moms who can’t or choose not to rely solely on breastfeeding.

SIDS is the leading cause of death of babies between 1 month and one year of age; its cause is unknown, but certain practices including breastfeeding and putting babies to sleep on their back have been associated with huge advances in prevention. Yet breastfeeding’s protective qualities aren’t fully understood; some theorize its SIDS-preventative benefits come from breast milk’s effect on babies’ immune systems and sleep patterns, while others suggest it’s the bonding and physical closeness of the act that keep parents attentive and babies safe. Still others suggest the practice of breastfeeding correlates with generally healthier and more educated home environments, which all works together to protect against SIDS.

To determine the relationship between duration of breastfeeding and SIDS risk, the researchers analyzed eight major international studies that examined 2,259 cases of SIDS and 6,894 control infants where death did not occur. This large collective sample demonstrated the consistency of findings despite differing cultural behaviors across countries, and provides convincing evidence of the reliability of the findings.

“These results are very powerful,” said researcher Kawai Tanabe, of the University of Virginia School of Medicine, and one of the study’s authors. “Breastfeeding is beneficial for so many reasons, and this is really an important one.”

Based on their results, the researchers are calling for “ongoing concerted efforts” to increase rates of breastfeeding around the world. (The World Health Organization has established a goal of having more than half of infants worldwide being breastfed exclusively for at least six months by 2025.)

It remains unclear why breastfeeding partially prevents SIDS, though the researchers cite factors such immune benefits and effects on infant sleeping patterns as possible mechanisms.

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