Weight loss lowers breast cancer risk in susceptible women

An international team has found that women with a mutation in the gene BRCA1, which predisposes them to breast cancer, are 65 per cent less likely to develop the disease if they lose at least 10 pounds (4.5g) between 18 and 30 years old.

The study, published in Breast Cancer Research​ (2005, 7:R833-R843), is further evidence of the link between obesity and higher risk of cancer. It will lend support to increasingly urgent calls to tackle the growing weight problem among young people.

Steven Narod from the University of Toronto, Canada, and colleagues from universities in Canada, the USA and Poland studied more than 2000 women from five countries who all had a mutation in one of the breast cancer susceptibility genes BRCA1 and BRCA2.

Around one in 200 women has a mutation in at least one of these genes and about 80 per cent of these women will get breast cancer, compared to 8-10 percent of women without the mutation.

The researchers split the women into two groups; the first had been diagnosed with breast cancer while the second group had not.

Each member of the first group was matched with a woman from the second group who was the same age, carried a mutation in the same gene and lived in the same country.

After comparing the two groups, the researchers reported that for women with a mutation in BRCA1, weight loss of at least 10 pounds between the ages of 18 and 30 was associated with a 65 per cent reduction in cancer risk when aged 30-40 years old.

But the women in this group who gained 10 pounds or more during the same time of their lives were 44 per cent more at risk of developing breast cancer if they had two children or more.

Obesity rates among European women are increasing, with one in five women in at least seven European countries now classified as obese, according to the International Obesity Task Force.

However no association between weight loss and breast cancer risk was shown in BRCA2 mutation carriers, and the study findings cannot be applied to the many more women without these two genetic mutations.

Yet other research has shown that weight gain raises the risk of breast cancer, possibly as a result of hormones that interact with gene mutations when a woman puts on weight.