A reply to Lars Bo Andersen and Bengt Saltin

Lars Bo Andersen and Bengt Saltin are concerned about the simulation study and state that `̀ there are great problems with all the key parameters’ ’ . They make some comments on the importance of careful selection of risk factor prevalence data and relative risk (RR) estimates relating risk factors to IHD mortality. The Prevent model used for the study was developed within a European collaborative project on Public Health Models involving the Dutch model makers and with participants from Sweden, England, and Denmark. Great efforts were taken to choose all input data carefully. Obviously Lars Bo Andersen and Bengt Saltin are dissatis ed with the choices made by the project group, who discussed the available epidemiological data and selected RRs after a thorough literature search taking into account the choices of risk factor exposure levels (1). Prevalence of hypertension and hypercholesterolaemia were derived from the third Danish MONICA survey carried out in 1991 ± 92, because these risk factors are known to be important for IHD and because no such data exist from a national health examination survey (involving blood measurements). National prevalence data of physical activity were available from the Danish Health Interview Survey, 1994. Because of the long-term effect of smoking on mortality from IHD and the other smoking-related diseases included in the model, it was of great importance that past trends of smoking prevalence were taken into account in the simulations. Therefore, nationwide personal interview data on smoking habits during the period 1973 ± 92 were included in the model. The main concern of Lars Bo Andersen and Bengt Saltin is that prevalence of physical inactivity and RRs for IHD are low. They are frustrated that the national data on prevalence of sedentary people (below age 65) is substantially lower than in the MONICA study and they are dissatis ed with my choice of RR from the meta-analysis of Berlin and Colditz (2), because their own RR estimates from the Danish MONICA study were higher according to a new paper (3, in press). Results based on the metaanalysis of Berlin and Colditz better guarantee reliable RR estimates than estimates from a single study from a local region. An important point here is that a large sample is needed to ensure that enough IHD deaths occur within a reasonable time of follow-up among people reporting no illness when questions on physical activity were asked in order to get valid RR estimates. RR might be overestimated due to confounding problems introduced if data on physical inactivity among ill persons were included. Lars Bo Andersen and Bengt Saltin state that `̀ For unknown reasons Brù nnum-Hansen chose a scenario in which all sedentary people should increase their physical activity level to light activity’ ’ , although this scenario is described explicitly in the paper and especially emphasized as one of the goals in the Danish Government programme on public health and health promotion, 1999 ± 2008 (4). It seems necessary to stress that the purpose of the study was to compare the health bene ts of selected preventive interventions and not to calculate simple aetiological fractions and discuss which risk factor causes most IHD deaths. The Prevent model simulation of the future reduction in the number of deaths depends on risk factor prevalence, RRs, time dimensions, and demography. Some epidemiological data are less valid for the older part of the population compared with younger people and in the discussion section of the article it was explained why results were given for ages below 65 years only. Exposure to some risk factors such as physical inactivity is strongly related to age. It is evident that the prevented number of IHD deaths would increase dramatically if the ``nobody sedentary’ ’ scenario were simulated for the entire population because of the high prevalence of sedentary elderly people. Lars Bo Andersen and Bengt Saltin argue that