Cancers attributable to dietary factors in the UK in 2010

The risks associated with consumption of 1 g per day of fruit or of vegetables are shown in Table 1 . As we are concerned with quantifying the effect of a deficit in consumption, they are presented as the risk associated with a decreased intake of 1 g per day. These risks derive from the simple means of the values from three meta-analyses: those of Riboli and Norat (2003) , WCRF (2007) and, except for laryngeal cancer, Soerjomataram et al (2010) . (The value for the protective effect of vegetables on cancers of the oral cavity and pharynx in the meta-analysis of Soerjomataram et al (2010) was quite implausible, implying a reduction in risk of 1.4% per gram per day. We substituted the value for upper aero-digestive tract cancers from the multi-centre European prospective study (EPIC) of 0.29% per gram per day ( Boeing et al, 2006 )). The values from the latter were reported as relative risk per gram increase in daily consumption of fruit and vegetables. For the others, the excess relative risk for a decrease of 1 g of vegetables or fruit consumed was estimated by assuming a log-linear relationship between exposure and risk, so that: where x is the exposure level (in grams per day) and RR x the relative risk for x grams per day. The latent period (or interval between ‘exposure’ to fruit and vegetables and the appropriate decrease in risk of these cancers) is not known. Prospective studies of diet and cancer (from which the estimates of relative risk are mostly drawn) involve follow-up periods (between estimated dietary intake and cancer onset) of several years. For the cohort studies contributing to the meta-analyses of WCRF, 10 studies of lung cancer and 6 of stomach cancer reported the mean duration of follow-up; the simple means were 15.2 and 10.3 years, respectively. There are a few cohort studies on upper GI cancers: the follow-up periods in the EPIC study ( González et al, 2006 ) and Japanese JPHC studies ( Yamaji et al, 2008 ) were 6.5 and 7.7 years, respectively. For the purposes of estimating attributable fraction, we assume a mean latency of 10 years, and thus examine the effects on cancers occurring in 2010 of sub-optimal levels of fruit and vegetable consumption in 2000. Consumption of fruit and vegetables, in grams per week, by age group and sex, is available for 2000–2001 from the National Diet & Nutrition Survey ( FSA, 2004 ; Table 2.1). The mean consumption, by age group, is shown in Table 2 . The target consumption of 400 g per day was not achieved at any age, and the young, in particular, had a low consumption of such items. The National Diet & Nutrition Survey also provides the distribution of intake of fruit and vegetables in the British population, in terms of the cumulative percentage of individuals (by sex and age group) consuming 0, <1, <2, …, >5 portions of fruit and vegetables daily ( FSA, 2004 ; Table 2.3). The populations of each sex were dichotomised into two age groups (<50 and 50–64), and ‘portions’ were converted into grams (of fruit and vegetables), such that the mean daily intake corresponded to the values in Table 2 . Table 3 shows the results in terms of the proportions of the population at seven different levels of consumption of fruit and vegetables. To calculate the deficit in consumption of fruit and vegetables relative to a target of 400 g per day for both, the deficit in each sex and age group (19–49, 50–64) was calculated from Table 2 . For example, the deficit in older men (50–64) was, on average, 216 g per day (400−(162+122)). The total deficit is partitioned into deficits of fruit and vegetables, so that the same ratio of vegetables to fruit that was being eaten in 2000–1 is maintained. Thus, the 400 g per day target for consumption in men in the age group of 50–64 years is partitioned in the ratio of 162:122 ( Table 2 ); i.e., 228 g per day vegetables and 172 g per day fruit ( Table 3 ). The deficit of each in the different consumption categories in men and women aged <50 years and in the age group of 50–64 is shown in Table 3 . For each cancer, the relative risk in 2010 in the four age–sex strata is calculated from the deficit in consumption 10 years earlier (2000–2001), with the risk for fruit and vegetables calculated separately according to the following formula: where R g is the relative risk for a deficit of 1 g per day of fruit or vegetables ( Table 1 ) and G x is the deficit in consumption (as shown in Table 3 ) in consumption category x. The benefits of fruit and vegetables are considered to be multiplicative in their effect, so that Population-attributable fractions were calculated for each of the four sex–age groups in Table 3 according to the following formula: where p x is the proportion of population in consumption category x and ERR x the excess relative risk (RR( f and v )−1) in consumption category x . Table 4 shows the PAFs and the estimated number of cases ‘caused’ in 2010 by these deficits in consumption of fruit and vegetables 10 years earlier. The cancers for which the greatest proportion of cases may be related to low intake of fruit and vegetables are the oral cavity and pharynx (56%), oesophagus (46%) and larynx (45%). Although only 9% of lung cancer cases may be related to low intake of fruit (there is no excess risk of lung cancer from low intake of vegetables), the actual number of cases (3567) represents almost one-quarter of the total number of cancers attributable to low intake of fruit and vegetables (14 902: Table 5 ). Table 5 sums the excess numbers of cases at the five sites, caused by low consumption of fruit and vegetables, and expresses these numbers as a fraction of the total burden of (incident) cancer. The estimate is 6.1% cancers in men and 3.4% in women, or 4.7% of cancers overall.