The research published in the open access journal BMC Cancer suggests that while staying positive has a protective role, adverse life events such as the loss of a parent or close relative, divorce or the loss of a spouse can increase a woman's risk of developing the disease.
Ronit Peled from the Faculty of Health Sciences at Ben-Gurion University of the Negev, Israel, led a team of researchers who questioned 255 women with breast cancer and 367 healthy controls about their life experiences and evaluated their levels of happiness, optimism, anxiety and depression prior to diagnosis.
Peled said, "Young women who have been exposed to a number of negative life events should be considered an 'at-risk' group for breast cancer and should be treated accordingly".
The researchers do point out that women were interviewed after their diagnosis, which may colour their recall of their past emotional state somewhat negatively.
However, according to Peled, "We can carefully say that experiencing more than one severe and/or mild to moderate life event is a risk factor for breast cancer among young women.
On the other hand, a general feeling of happiness and optimism can play a protective role".
The researchers point out that, "The mechanism in which the central nervous, hormonal and immune systems interact and how behaviour and external events modulate these three systems is not fully understood".
As such, they suggest that "The relationship between happiness and health should be examined in future studies and relevant preventative initiatives should be developed."