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.

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."

Paper

'What can Mendelian randomization tell us about causes of cancer?' by Mariosa D, Carreras-Torres R, Martin RM, Johansson M, Brennan P in International Journal of Epidemiology