Weight gain increases risk of cancers

Obesity, an invitation to many diseasesUncontrolled body weight poses a serious danger to health. Also the probability of dying from certain diseases especially cancer, is higher in obese people, reports Sade Oguntola.

BEING obese or even overweight may increase a person’s risk of developing up to a dozen different types of cancers, according to a major new study further attesting to the link between obesity and cancers stall parts of the body.

Doctors have long suspected a link between weight gain and other health problems such as diabetes, heart disease, stroke, early death and certain cancers, including colon and breast cancers. But a study, published in the journal, Lancet, suggested it could also increase chances for cancer of the osophagus, thyroid, kidney, uterus and gall bladder, among others.

Obesity is a major issue worldwide and also raises the risk of diseases such as Type 2 diabetes and heart problems. The World Health Organisation said about 400 million people are obese worldwide.

The researchers came to this conclusion after they compiled data from 141 studies and considered more types of cancers and more diverse populations than had been done previously. The research covered more than 280,000 cases from North America to Europe, Australia and Asia.

The subjects, both overweight and normal-weight people, were followed for about 9 to 15 years, with researchers tracking their body mass index, or BMI — a calculation based on weight and height — and correlating it with incidents of cancer.

In men, an average weight gain of 33 pounds increased the risk of osophageal cancer by 52 percent, thyroid cancer by 33 percent, and colon and kidney cancers each by 24 percent, the research found.

In women, a weight gain of 29 pounds increased the risk of cancer in the uterus and gall bladder by nearly 60 per cent, osophagus by 51 per cent and kidney by 34 per cent, the study said.

However, despite the study suggesting that obesity increases a person’s risk of developing up to a dozen different types of cancers, the researchers pointed out that there is no definitive proof that being fat in itself causes cancer.

Scientists are not sure how being overweight could make people more susceptible to cancer. One of the hypotheses by Dr. David Robbins, a gastroenterologist at Beth Israel Medical Center in New York, is that the presence of excess fat cells could affect the levels of hormones in the body and that may favour the development of tumours in humans.

Before now, the American Cancer Society had said there was an association between body-mass index (BMI) and death from most forms of cancer, concluding that no less than 90,000 cancer deaths a year are related to weight as far back as year 2003.

It was in reaction to a study, published in the April 24, 2003 issue of the New England Journal of Medicine, that identified several forms of cancer not previously linked widely to unhealthy body weight, including stomach (in men), liver, pancreas, prostate, non-Hodgkin lymphoma, multiple myeloma, cervix, and ovary.

However, many people have not acknowledged the contribution of obesity to chronic diseases in general and to cancer in particular. For example, women are very concerned about breast cancer, but few understand that obesity doubles their risk of getting and dying from the disease.

Also, many are not aware that cancers have a worse outcome in obese patients. According to Professor O. O. Mbonu while delivering a lecture, entitled”Prostate Cancer: Burden and Risk Factors”, at a workshop to commemorate the birthday of Professor Jide Ajayi, a renowned cancer expert at the Olabisi Onabanjo University Teaching Hospital, Sagamu, the fact that obesity increases a person’s chances of having cancer has been controversial in some quarters. However, he said, the chance of dying from cancer is higher than in those that are obese because the cancer tends to be more aggressive.

The fact that obesity also predisposes women to breast cancer was also confirmed by Prof. Funmilayo Olapade, Department of Medicine & Human Genetics, University of Chicago, at the same event in honour of Prof. Jide Ajayi, who attributed this to inflammatory processes that occur in cells that are undergoing mutation.

Another explanation given for cases of breast cancer in women that had attained menopause, according to Joanne Dorgan of Fox Chase Cancer Center in Philadelphia, is that after a woman’s ovaries shut down, fat cells become the main source of ostrogen production. Consequently, heavier women are exposed to more circulating ostrogen, which can fuel the growth of abnormal breast cells. But in women of reproductive age, obesity often causes disruption of the ovulatory cycle; so the breast cells of heavier women get less estrogen exposure.

Another explanation given by an expert in the British Medical Journal was that obesity was more closely linked to colon cancer in men than in women probably because it is fat around the middle, rather than body mass index or fat in general, that causes colon cancer. In men, BMI correlates with abdominal fat better than in women.

Meanwhile, researchers are warning that fat is becoming the new tobacco. Conceivably, as cigarette smoking (which is the largest cause of cancers in developed countries) decreases, excess body weight could become the dominant lifestyle factor that contributes to cancer occurrence in such countries. And, unlike smoking, it is not known whether it is too late to lower cancer risks once the weight is already on.

Because many studies have found that fatter people are more likely to get cancer, experts often recommend losing weight to reduce cancer risk. “The simple message is that, if you manage to keep a healthy body weight, you will have a lower risk of developing cancer,” said Ed Yong, of Cancer Research, United Kingdom.