New mothers who successfully breastfeed their babies are less likely to get postnatal depression, new research suggests.
Expectant mothers who plan to breastfeed after they have given birth but are unable to are at the highest risk of developing the condition, experts found.
Around 13pc of new mothers experience postpartum depression within 14 weeks of giving birth.
As well as posing serious mental health problems for the mother, it can have significant effects on the newborn's cognitive, social and physical development.
Researchers said the effect that breastfeeding has on postnatal depression is not well understood, and they set out to investigate whether there is a link between the two.
The authors, from the UK and Spain, surveyed women who had 14,000 babies in the Bristol area during the 1990s when their children were two, eight, 21 and 32 months old.
They also examined whether the women suffered depression during their pregnancy so they could take into account previous mental health conditions.
Their study, in the journal Maternal and Child Health, found mothers who planned to breastfeed and who went on to do so were around 50pc less likely to become depressed than mothers who had not planned to - and did not - breastfeed.
Those who planned to breastfeed but did not go on to do so were more than twice as likely to become depressed as mothers who had not planned to and did not.
"The lowest risk of postpartum depression was found among women who had planned to breastfeed and who had actually breastfed," the authors wrote.