Fat linked to cancer risk in new study

By ROSALEEN MacBRAYNE AND AGENCIES

Fat New Zealanders are living with an increased risk of developing cancer.

A study has found that the more overweight a person is, the higher the chance of developing almost all types of cancer.

The American Cancer Society study, which tracked 900,000 people over 16 years, found excess weight to be a likely factor in 20 per cent of all cancer deaths in women and 14 per cent in men.

The study, published this week in the New England Journal of Medicine, is the largest made, and the first to quantify the risk for all forms of cancer.

A range of cancers, including stomach, prostate and cervix cancers, have been found to have some link to weight.



The New Zealand Ministry of Health is developing a national strategy to curb the rising numbers of New Zealanders dying prematurely from obesity-related illness.

Nearly four in 10 adults in New Zealand are overweight, and by 2011 it is predicted that three in 10 will be medically obese.

The Herald has examined the problems of obesity in children in a three-part series this week.



Doctors had known of a connection between fat and some cancers for some time, but the US study found the link "really was the rule more than the exception", said lead researcher Eugenia Calle.

"The more weight you have, the higher the risk," she said. "Losing any kind of weight would help."

Donna Ryan, head of clinical research at the Pennington Biomedical Research Centre in Baton Rouge, Louisiana, said: "The study is absolutely convincing. And therefore it's frightening. Because of the magnitude and strength of the study, it's irrefutable."

The study, which began in 1982 when all the participants were cancer-free, found a variety of reasons for the link between weight and cancer.

Fat raises the amount of oestrogen in the blood, increasing the risk of cancers in the female reproductive system.

It increases the risk of acid reflux, which can cause cancer of the oesophagus.

It raises levels of insulin, prompting the body to create a hormone which causes cells to multiply, just like cancer.

Obesity also makes cancer harder to diagnose and treat. Lumps and bumps are harder to see or feel and some patients do not fit into CAT scanners, says Dr Robert Mayer of Harvard Medical School.

Fat people might avoid regular visits to doctors, "possibly because of their appearance or because they just shy away from physicians".

The study has confirmed earlier research findings that fat contributes to cancers of the breast and uterus, colon and rectum, kidney, oesophagus and gall bladder.

And it adds eight more cancers to the list - cancers of the cervix and ovary, multiple myeloma, non-Hodgkins lymphoma, pancreas, liver and, in men, the stomach and prostate. Researchers found no connection between fat and brain, skin and bladder cancers.

Obesity is on the rise in the industrialised world - including New Zealand - and the study suggests that the incidence of cancer, and the cost of treating it, will also continue to increase.





One-quarter of all deaths in New Zealand are from cancers.

The most common are lung, colorectal and prostate for men, and breast for women.

The study found that the heaviest men had a 52 per cent higher cancer death rate than those of normal weight, and the heaviest women had a 62 per cent higher death rate.

Obese men were more than four times more likely to die from liver cancer than thin men, said the research.

Obese women were six times more at risk of cancer of the uterus.

"This is going to have an impact on cancer rates in New Zealand," said the Cancer Society's health promotion manager, Carolyn Watts.



Fat was becoming as big a risk factor for cancer as smoking, and was a cause for concern in New Zealand, where the rate of obesity was quite high and increasing.



Most people knew of the link between diet, physical activity and weight and heart disease. The relationship to cancer was less well known.



Ms Watts said an emphasis should be placed on preventing childhood obesity because the study - covering people over 16 years of age - showed the cancers developed in adulthood.