Mothers who work outside the home are less depressed and in better general health than their unemployed peers, a new study finds.

Researchers interviewed over 1,300 mothers throughout their child’s infancy, preschool years and into elementary school. Working mothers reported fewer symptoms of depression and were more likely to rate their health as “excellent,” compared to the unemployed moms – at least until the child entered preschool.

Stay-at-home moms may be more socially isolated than working moms, researchers noted, increasing their risk of being depressed. Also, being at home with young children may be more stressful than being at work, they theorized, which may explain why the association disappears when kids enter preschool.

The findings were published in the Journal of Family Psychology and were based on women who enrolled in the U.S. National Institute of Child Health and Human Development Study of Early Child Care and Youth Development.