Milk may be culprit in breast cancer

By JEREMY LAURANCE

Tall, thin teenage girls who put on a growth spurt at puberty are at highest risk of breast cancer - and milk may be the culprit.

Their shorter, chubbier sisters are at lower risk and remain so throughout their adult lives until they reach the menopause.

The findings from a Danish study of more than 117,000 women confirm that height is a risk factor for breast cancer and show that it is growth in childhood that has the greatest influence.

The study, published in the New England Journal of Medicine, could help explain one of the greatest puzzles of breast cancer - why the disease has seen a global increase over the last 50 years.

The answer may be that it is linked to the increase in average heights, driven by changing diets. And the journal calls for more research into one possible dietary factor behind both trends: the consumption of milk.

An increase in milk drinking has been suggested as a factor behind the large increase in average heights in Japan. As the Japanese adopted a more Western diet in the two decades after World War II, 12-year-old girls gained 15cm in height on average.

That gain has been paralleled 30 years later by an increase in breast cancer in the same generation of women which has doubled from 40 to 80 cases per 100,000 population.

Writing in the Journal, Karin Michels and Walter Willett of Harvard Medical School, Boston, say that milk may play an important role because it contains animal protein and a high level of anabolic hormones.

"Recent findings have confirmed that milk consumption does increase the circulating levels of insulin-like growth factor 1 and is associated with higher stature. Understanding how these and other factors are related to childhood growth and to the risk of breast cancer will not be an easy task but it is one that deserves serious attention," they say.

The Danish study, by researchers from the Epidemiology Science Centre in Copenhagen, shows that the speed of growth between the ages of 8 and 14 has the greatest influence on the risk of breast cancer in adult life. The researchers used school records to establish the girls' measurements and linked these with the later development of the disease.

The findings show that those whose peak year of growth occurred between the ages of 13 and 14 had a 16 per cent lower risk of breast cancer than those whose peak growth occurred earlier, between 10 and 11. Girls who were tallest by the age of 14 had the highest risk.

The researchers also found that girls who were overweight at puberty had a lower risk of breast cancer. Overweight girls tend to start menstruating earlier which is known to increase the risk. But the new findings suggest that that effect is outweighed by the oestrogen hormones produced by the extra fatty tissue which alter the growth of the breast.

After the menopause, overweight women are at higher risk of breast cancer.

- INDEPENDENT