Mothers who give birth through a cesarean section could pass on stress to babies through hormones in breast milk, according to a New Zealand study out Wednesday. Researchers at the University of Auckland's Liggins Institute analyzed breast milk samples from 650 mothers when their babies were three to four months old.

The findings revealed levels of the stress hormone, cortisol, were higher in the milk of mothers who delivered their babies by C-section or who had no partner at home.

As well as a major regulator of the body's stress response, cortisol was an important influencer of mood and growth, researcher Shikha Pundir said in a statement.