Obesity-related cancers on the rise

Eveline Gan

SINGAPORE — It is well known that excess weight increases a person’s risk of developing chronic illnesses such as heart disease, stroke and diabetes. Recent research has also suggested that its bad reputation extends to cancer risk.

A new study has found that obesity, defined as a high body mass index (BMI) of 25 or greater, is responsible for an estimated 500,000 cancers a year worldwide. It was published online last November in The Lancet Oncology.

The study said obesity-related cancers pose a greater problem to women than men due to oestrogen-driven cancers such as endometrial (womb) and breast cancer.

Singapore’s obesity rate has climbed 1 per cent each year, from 2004 to 2010, showed the 2010 National Health Survey. About 11 per cent of Singapore adults now grapple with obesity.

RISE IN COLORECTAL CANCER IN MEN AND BREAST CANCER IN WOMEN

The local population is seeing a rise in cancers that are commonly linked to obesity such as colorectal and breast cancers.

Other obesity-related cancers include cancer of the womb, pancreas, ovaries, kidney and gallbladder, to name a few, said Dr Wong Seng Weng, medical director and consultant at The Cancer Centre, a Singapore Medical Group clinic.

This is even when the incidence of certain cancers, such as those commonly associated with infections such as cervical cancer and liver cancer, has fallen in the past years, said Dr Raymond Ng, senior consultant at the Division of Medical Oncology at National Cancer Centre Singapore.

Colorectal cancer is currently the most common cancer among Singapore men. For local women, it is breast cancer.

Dr Wong estimated that one-third to half of the patients under his care have been overweight for many years before their cancer diagnosis.

One such patient is Mdm Helen Tan, a 51-year-old teacher who asked that her real name not be used as her friends and colleagues do not know about her condition.

When she was diagnosed with cancer a year ago, she weighed 90kg — her heaviest. That put Mdm Tan, who stands at 165cm, at a BMI of 33, which is in the high-risk category for chronic diseases.

HOW EXCESS WEIGHT MAY INCREASE CANCER RISK

While obesity on its own may not be the main culprit for cancer as other factors such as family history and diet play a part too, excess body weight has been associated with an increase in oestrogen (female hormones), said Dr Wong.

He explained: “Fat tissue has an enzyme known as aromatase that converts substances in the body into oestrogen. We know that several cancers in women such as breast and endometrial cancer are related to the stimulation by oestrogen.”

Too much body weight also increases the body’s resistance to the hormone insulin, which controls blood sugar levels.

“The excess production of insulin and related substances known as insulin-like growth factors promotes cell growth, including cancer cells,” said Dr Wong.

If obesity continues on its upward trend, Dr Wong warned that it is likely to overtake smoking as the top reversible factor causing cancer worldwide in the next few decades.

DIFFERENT BMI GUIDELINES FOR ASIANS

The study in The Lancet Oncology suggested that a quarter of obesity-related cancers could possibly be avoided if people kept their BMI within an acceptable range. The study defined a high BMI as 25 or greater.

However, this is not the case for Asians. Dr Ng said a BMI of 23 and above is generally considered unhealthy in the Asian population.

“One should not just try to avoid obesity alone, but to aim for a BMI of under 25, and if possible, stay within the ideal range of 18.5 to 22.9. Eat healthy and exercise regularly,” he advised.

Having recently completed her treatment for advanced breast cancer, Mdm Tan is eager to bid obesity goodbye to lower her risk of the cancer recurring.

For breast cancer in post-menopause cases, factors such as obesity, high-fat and low-fibre diets, and a lack of exercise are associated with a higher risk of relapse following treatment, said Dr Wong.

As such, overweight cancer survivors are often encouraged to go on a weight management programme after they have completed their treatment.

With a dietitian’s help, Mdm Tan has learnt to cut down on her food portions. She also exercises every morning for 30 to 40 minutes. In six months, she has shaved off 8kg and aims to lose another 20kg.

“If you ask me to choose between going through cancer treatment again and losing weight, I’ll choose the latter. It’s easier to diet and exercise,” she said.