Women who are underweight as teenagers are more than four times more likely to develop breast cancer before the menopause than those who are obese, a study has found.
Those with a body mass index (BMI) of less than 18.5 between the ages of 18-24 are the most likely to be diagnosed with the disease while they are young.
The more obese a woman is, the lower her risk of breast cancer before going through the menopause, researchers found. However, after the menopause fatter women are more likely to develop breast cancer.
Experts believe lower levels of the hormones oestrogen, progesterone and testosterone and lower breast tissue density are likely to have a protective effect for obese women prior to the menopause.
Baroness Morgan, chief executive at Breast Cancer Now which helped fund the research, said: ‘This is the strongest evidence yet that having a higher BMI when you are younger lowers your risk of breast cancer before the menopause. But we must be really clear that weight gain should not be considered an approach to prevent breast cancer.
‘We need to understand the biological reasons behind this phenomenon at a molecular level
‘If we could find a way to mimic the chemical changes in the body in response to body fat that are causing this protective effect, without weight gain being required, it could ultimately lead to a new way to prevent this devastating disease.’