Women who breastfeed have a reduced risk of developing diabetes, a new study reports. In mouse models, lactation improved glucose tolerance and increased beta-cell mass three weeks post-delivery. Prolactin produced as a result of lactation induced serotonin production of beta cells. Findings suggest serotonin mediates the long-term beneficial effects of lactation of female metabolic health by increasing beta-cell proliferation and reducing oxidative stress in beta-cells.