Benefits of lifestyle interventions: precise input estimates needed – Authors' reply

Abstract

We agree with E de Vries and colleagues that it is preferable to restrict estimates of the potential benefits of physical exercise to colonic cancer because of the inconsistent relation with rectal cancer; however, this restriction would have minimal effect on our main results and we believe we are unlikely to have overestimated total expenditure averted from colorectal cancer. Expenditure averted from reductions in colorectal cancer was less than 1% of the total expenditure averted over a 20-year period. This is partly because we assumed a conservative 17 years from implementation of increased active travel to the achievement of 50% of the beneficial effect. However even at full effect, reductions in incident cases of colorectal cancer were estimated to be 5%. We did take into account differences in relative risk reduction by sex by use of average effects from Woodcock and colleagues1Woodcock J Edwards P Tonne C et al.Public health benefits of strategies to reduce greenhouse-gas emissions: urban land transport.Lancet. 2009; 374: 1930-1943Summary Full Text Full Text PDF PubMed Scopus (751) Google Scholar across both sexes. We applied slightly lower risk reductions than those proposed by de Vries and colleagues for colonic cancer2de Vries E Soerjomataram I Lemmens VE et al.Lifestyle changes and reduction of colon cancer incidence in Europe: a scenario study of physical activity promotion and weight reduction.Eur J Cancer. 2010; 46: 2605-2616Summary Full Text Full Text PDF PubMed Scopus (48) Google Scholar for at least 30 min of moderate to intense physical activity, 5 days per week. This is because we used the results from Woodcock and colleagues1Woodcock J Edwards P Tonne C et al.Public health benefits of strategies to reduce greenhouse-gas emissions: urban land transport.Lancet. 2009; 374: 1930-1943Summary Full Text Full Text PDF PubMed Scopus (751) Google Scholar based on the systematic review by Harriss and colleagues.3Harriss DJ Atkinson G Batterham A et al.Lifestyle factors and colorectal cancer risk (2): a systematic review and meta-analysis of associations with leisure-time physical activity.Colorectal Dis. 2009; 11: 689-701Crossref PubMed Scopus (158) Google Scholar Conservatively we have also assumed no benefit from reducing cancers other than colorectal and breast cancer that might be related to physical inactivity.4Friedenreich CM Neilson HK Lynch BM State of the epidemiological evidence on physical activity and cancer prevention.Eur J Cancer. 2010; 46: 2593-2604Summary Full Text Full Text PDF PubMed Scopus (337) Google Scholar Our sensitivity analyses using a range of assumptions showed that the results were invariably positive but particularly sensitive to assumptions about lag times between the increase in active travel and changes in health outcomes. We encourage researchers on the relation between physical activity and health outcomes to consider improving estimates of the variables that our paper and the paper by Woodcock and colleagues2de Vries E Soerjomataram I Lemmens VE et al.Lifestyle changes and reduction of colon cancer incidence in Europe: a scenario study of physical activity promotion and weight reduction.Eur J Cancer. 2010; 46: 2605-2616Summary Full Text Full Text PDF PubMed Scopus (48) Google Scholar identified as most important for health and economic effects, particularly by reducing uncertainties about the shapes of the dose response curves and the time lag between behaviour change and change in risk of the various health outcomes. We declare that we have no conflicts of interest. Benefits of lifestyle interventions: precise input estimates neededJames Jarrett and colleagues (June 9, p 2198)1 developed an excellent scenario regarding the health and economic effects of increasing active travel in urban England and Wales. Although they state that there is an established link between physical activity and colon cancer, Jarrett and colleagues modelled effects for colorectal cancer. This will overestimate any preventive effects because no convincing effects of increased physical activity have been shown for rectal cancer, which represented 38% of all colorectal cancer cases in the UK in 2009. Full-Text PDF