The prevalence of excess body weight and obesity is rapidly increasing worldwide. Apart from several conditions like diabetes, heart disease, liver and gall bladder disorders, cancers have also been associated with obesity. There is sufficient evidence to link certain forms of cancers to obesity.
Definition of obesity
The World Health Organisation (WHO) defines obesity as “an abnormal or excessive fat accumulation in adipose tissue, to the extent that health is impaired”.
The currently accepted criteria for overweight is defined as body mass index (BMI) levels greater than 25 kg/m2 and obesity as BMI of 30 kg/m2.
Apart from BMI, obesity is also associated with several lifestyle changes including increased high fat/energy-rich food intake and reduced physical activity.
Worldwide 1.1 billion people are currently estimated to be overweight, at least 300 million of them obese.
Worldwide, cancer affects roughly 22 million persons who are living with the condition. This makes it a major public health problem.
Association between cancers and obesity
The International Agency for Research on Cancer has assessed the association between cancers and obesity. Their focus was on certain cancers like cancers of the colon, female breast (especially in women who have achieved menopause), endometrial or womb cancers, kidney and adenocarcinoma of the esophagus. Other cancers linked to obesity include pancreatic, ovarian, cervical and blood cancers.
Preventable causes of cancer
At present some of the most important preventable causes of cancer include cigarette consumption followed by obesity.
Studies have shown that in the European Union excess body weight accounts for 5% of all incident cancers, 3.5% in men and 6.5% in women. This means that additional 27 000 male and 45 000 female cancer cases each year are associated with obesity.
Apart from causing cancers, obesity is also linked to increased risk of short term or reduced survival with cancers. Excess body weight in a study accounted for 14% of all deaths from cancer in men and 20% of those in women.
Breast cancer and obesity
Adult weight gain has been linked to obesity. The risk rises after menopause. Being overweight increases breast cancer risk after menopause. This is especially so among those who have never used of hormone replacement therapy.
Being overweight and obese also raises risk of the breast cancer coming back after therapy and poorer overall survival in both, pre- and postmenopausal women.
Endometrial or womb cancer and obesity
There is an estimated 2- and 5-fold risk increase of endometrial cancer among obese and overweight women. Contrary to breast cancer, the effect of obesity on endometrial cancer risk seems to remain constant throughout adult life and is not affected by achievement of menopause.
Colon and rectum cancer and obesity
There are studies that link bowel cancer with obesity. Relative risk estimates ranged from 1.2 to 2.0. Obesity may lead to development of colorectal cancer at an early stage and also cause recurrence of adenomatous polyps that are considered hallmark precursors of bowel cancer.
Kidney cancer and obesity
There is an increase in risk of renal cell carcinoma and obesity especially women, with high BMI irrespective of other risk factors such as hypertension and diabetes.
Esophagus cancer and obesity
In Western countries the incidence of oesophageal adenocarcinoma has risen along with rise of obesity rates. Studies show that there is an estimated 2–3-fold increased risk of adenocarcinoma of the esophagus with increasing BMI.
There is a possible increase in gastro-oesophageal reflux with obesity and this could be a causal link between esophagus cancers and obesity.
Prostate cancer and obesity
The International Agency for Research on Cancer has found no direct association between incidence of prostate cancer and obesity. However there is a connection between obesity and cancer progression.
Gallbladder cancer and obesity
Gallbladder cancer risk rises two-fold in overweight subjects. Excess weight has also been related to risk of deaths with gallbladder cancers in both men and women.