Family size makes no difference - looking after one child is enough to push stressed mothers to the edge.
Researchers from Duke University in North Carolina found that mothers had a higher risk of heart attack and other health problems than working women without children.
The team, whose findings appear in the journal Psychosomatic Medicine, studied 109 women working in clerical and service jobs and measured the stress-related hormones in their urine over two days. Hormone levels were correlated with factors such as whether the women were single or married and how many children they had.
The study, funded by the National Heart, Lung and Blood Institute, found that stress hormones, such as cortisol which is thought to suppress the immune system if it remains high, rose each morning and stayed high all day. While job strain was about the same in all women, working mothers suffered significantly more strain at home.
Dr Redford Williams, chief of behavioural medicine at Duke, said: "The good news would be that working mothers' stress levels don't go up with the number of children in the home. The bad news is it only takes one to boost that stress level."Reuse content