Cancers attributable to overweight and obesity in the UK in 2010

The estimates of risk associated with overweight (BMI 25<30 kg m ) and obesity (BMI 30+ kg m ), relative to a BMI ⩽ 25 kg m , for the seven cancers, are shown in Table 1 . The estimates of relative risk for an increase of 5 kg m from the meta-analyses by WCRF (2007) have been used for the category ‘overweight’. Assuming a constant rate of increase in risk with BMI, the square of this value was taken for the category ‘obese’. For postmenopausal breast cancer, WCRF reported that the increase in risk was 8% per BMI increase of 5 kg m for cohort studies (17 considered) and 13% per BMI increase of 5 kg m for case–control studies (48 considered). The estimates from the meta-analyses of Bergstrom et al (2001) and Renehan et al (2008) were almost identical (12% per BMI increase of 5 kg m ), and thus this value has been selected. The latent period, or interval between ‘exposure’ to overweight/obesity and the appropriate increase in risk of these cancers, is not known. Renehan et al (2008) calculated the geometric mean duration of follow-up in the cohort studies available for a meta-analysis of relative risks due to overweight and obesity. The periods ranged from 8.4 years (for breast cancer) to 12.7 years (for gall bladder cancer). We therefore chose to assume that the latency between ‘exposure’ and outcome would be, on average, 10 years, and thus examine the effects on cancers occurring in 2010 from suboptimal levels of body mass in 2000. The proportion of adults in the age group of 19–64 who were overweight or obese in Great Britain in 2000–2001 is available from the National Diet and Nutrition Survey (FSA, 2004 ; Table 4.1). For older adults (aged ⩾ 65), we used the values for 2000 from the Health Survey for England ( Health and Social Care Information Centre, 2010 ). The results are shown in Table 2 . The number of oesophageal cancers diagnosed in 2010 was partitioned by histological subtype, according to the age- and sex-specific distribution observed in the UK Cancer registries reporting to Cancer Incidence in Five Continents, Volume VIII ( Parkin et al, 2002 ). These age-specific proportions were scaled to correspond to the crude proportions observed in the UK registries in 2000–2002 ( Curado et al, 2007 ), when adenocarcinomas comprised 69.9% of oesophageal cancers in men and 39.9% in women. The population-attributable fraction (PAF) was calculated for each sex–age group, corresponding to the level of overweight/obesity 10 years previously, according to the usual formula: where p 1 is the proportion of population overweight, p 2 the proportion of population obese, ERR 1 the excess relative risk (RR−1) for overweight and ERR 2 the excess relative risk (RR−1) for obesity. Table 3 shows the calculation of attributable fractions, and corresponding numbers of attributable cases, by age group and sex, for seven cancer types accepted to be causally related to excess body weight, assuming a 10-year latency between the presence of excess body mass and cancer risk. Table 4 summarises these results. An estimated 17 294 excess in cancer cases occurring in 2010 were due to overweight and obesity (5.5% of all cancers). The sites contributing most to this excess are large bowel (5172) and breast (4194).