Study links overeating to breast cancer risk

Overeating may increase a woman's chances of getting breast cancer, researchers suggest today. Going hungry and hard physical labour may be among the most effective defences against the disease.

Overeating may increase a woman's chances of getting breast cancer, researchers suggest today. Going hungry and hard physical labour may be among the most effective defences against the disease.

Breast cancer is much more common among women in industrialised countries than in those with more traditional lifestyles in the developing world. Scientists believe the explanation lies in the balance between energy intake and energy expenditure.

The number of calories consumed and expended in exercise affects hormone levels in the body, which in turn influence breast cancer risk. Women who eat less and exercise more may therefore cut their risk of breast cancer.

Saliva taken from women in Bolivia, the Democratic Republic of Congo, Nepal, Poland and the United States showed that those with the highest hormone levels (oestrogen and progesterone) had the highest risk of breast cancer. Hormone levels were in turn linked with the calories consumed.

The rate of breast cancer in America is almost twice that in the Congo and the progesterone concentration in the women's saliva was almost 10 per cent higher. The higher hormone levels in the US were linked with the higher calorie intake, twice that in the Congo.

Hormone levels and breast cancer risk fell between these extremes in the other countries but were also closely linked.

Professor Grazyna Jasienska, of the Institute of Public Health at Jagiellonian University, Cracow, Poland, writing in the British Medical Journal, says there is an important link between the risk of breast cancer and nutritional status. "The strength of the relation strongly suggests that it is an important biological phenomenon."

The influence of diet on the reproductive cycle is well known. Starvation can suppress ovulation and menstruation while access to unlimited food, as in America, encourages frequent monthly cycles and a high hormone concentration. No link has been found between low hormone doses in contraceptive pills and breast cancer.

Professor Jasienska said: "The risk of breast cancer may be modified if changes are made in a woman's lifestyle. An increase in physical activity and decrease in caloric intake may thus lead to lower concentrations of progesterone and oestrogen, resulting in a reduction in breast cancer risk."

Asked if dieting could reduce the risk of breast cancer, she said: "It is a logical conclusion. They [dieters] would be reducing their levels of oestrogen and progesterone. Post-menopausal women who have gained in weight by several pounds since their twenties have an increased risk of breast cancer. In pre-menopausal women, some people think it is calories that are important while others think it is exercise [that affects the risk]."

Exercise was better than dieting. "Dieting increases the risk of osteoporosis whereas exercise strengthens the bones. We know that exercise lowers hormone levels - but we don't know how much exercise or what kind. That is what we need to find out."