Skinny teens face greater breast cancer risk before menopause

‘Chemical changes’

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.’

Breast cancer is still the most common cancer in the UK, affecting one in eight women, yet has one of the lowest breast cancer survival rates in Western Europe.

Nearly a fifth of cases develop in women under the age of 50, so British researchers wanted to test who was most at risk.

In the biggest study of its kind, scientists followed 758,592 women, 13,082 of whom developed breast cancer. These included women from the US, where obesity rates are higher, and Japan, where women tend to be leaner, plus the UK and 12 other countries.

Led by the Institute of Cancer Research, London, the scientists wanted to test how BMI – which compares someone’s weight with their height – affected rates of the disease before the menopause. They collected information on women’s BMI at four age ranges. Those with a BMI of 18.5 or below are considered underweight, 18.5 to 25 is normal, above 25 is overweight and more than 30 is obese.

They found that those with the highest rates – of over 30 – when they were 18, were 4.2 times less likely to develop breast cancer than women in the lowest category. Being obese during all four age ranges, which were 18-24, 2534, 35-44 and 45-54 was associated with a lower risk.

Compared with those at the low end of a healthy BMI, between 18.5 and 22.9, every additional 1st 8lb extra reduced the risk by between 12 and 23 per cent, depending on age.

The research was published in the journal JAMA Oncology.