Effect of obesity on risk of cancer twice as large as previously thought

The effect of being overweight and obesity on risk of cancer is at least twice as large as previously thought, according to new findings by an international research team which included University of Bristol academics.

The study published in the International Journal of Epidemiology was led by the International Agency for Research on Cancer (IARC) and involved researchers from Bristol Medical School.

The team conducted genetic analyses on eight common obesity-related cancer types. They compared the genetic Mendelian randomization estimates of the association between body mass index (BMI) and cancer risk with the estimates from classical cohort studies.

Excess body fatness is already recognized as an important cause of cancer and has been estimated to account for six per cent of all cancers in high-income countries. According to the results of this new analysis, the proportion of cancers attributable to overweight and obesity is, in fact, substantially higher.

Professor Richard Martin, Professor of Clinical Epidemiology at the University of Bristol Medical School, said: “The importance of these analyses is that they suggest that the effect of being overweight on cancer risk has been underestimated in the past and that obesity plays an even more important role in cancer than previously suggested.”

Professor Andrew Goddard, president of the Royal College of Physicians said: “This analysis offers yet further evidence of the potentially devastating impact of obesity.

“Obesity is a chronic progressive disease with a wide range of damaging effects on the body. It not only increases the risk of cancer, but often leads to other health complications such as type 2 diabetes, dyslipidaemia, infertility, cardiovascular disease, liver disease and osteoarthritis.

“With effective treatment these complications can be improved or reversed. But if we’re to succeed in reducing the soaring rates of obesity in this country, we must recognise that it is not a lifestyle choice caused by individual greed but a disease caused by health inequalities, genetic influences and social factors.

“It is governments, not individuals, that can have an impact on the food environment through regulation and taxation, and by controlling availability and affordability. Governments can also promote physical activity by ensuring that facilities are available to local communities, and through legislation and public health initiatives.”