We combined global dose-response risk curves with country-year-age-sex-specific continuous exposure distributions so we could capture differences in risk across countries that result from heterogeneous smoking patterns. Because the risk reduction curves for former smokers must account for two dimensions-years since cessation and intensity of smoking before cessation-we scaled the risk reduction curves for former smokers to match their starting relative risk (when years since cessation equals zero) to the exposure-weighted relative risk among current smokers in that population. The PAF equation is specified in appendix 1 (p 28). For smoking tobacco use, the theoretical minimum risk exposure level is never smoking. Inputs to estimation of PAFs included prevalence of current and former smoking tobacco use, continuous exposure distributions, relative risks, and the theoretical minimum risk exposure level. We used the Disease Modelling Ordinary Differential Equation (DisMod ODE) solver to fit non-linear Bayesian meta-regressions for each health outcome. For cardiovascular and circulatory diseases and all other health outcomes, we used cigarette-equivalents per smoker per day as the exposure among current smokers, because dose is generally thought to be more important than duration of exposure for these health outcomes. For cancers and chronic obstructive pulmonary disease, we used pack-years as the exposure, allowing risk to reflect both duration and dose (cigarette-equivalents per day) of exposure. This process involved an extensive systematic review, covering 71 996 total search string hits, from which 902 prospective cohort and case-control studies were found to be eligible and from which data were extracted (Preferred Reporting Items for Systematic reviews and Meta-Analyses diagrams for each outcome are in appendix 1 ). To address this limitation, we estimated dose-response risk curves for both current and former smokers for 36 health outcomes using meta-regression ( appendix 1 p 26). Previous estimates of smoking-attributable burden in GBD relied on dichotomous exposures, despite well documented dose-response associations. Details on the modelling process for the supply-side data and approach to integrating the two sources of information are in appendix 1 (pp 22–23). Estimates of cigarette-equivalents consumed per smoker per day combine two sources of information: self-reported smoking patterns from household surveys and supply-side data on country-level consumption available from the Food and Agriculture Organization of the UN (1961–2013), the US Department of Agriculture (1960–2005), and Euromonitor (2002–17). We converted non-cigarette tobacco products to cigarette-equivalents on the basis of amount of tobacco (in g), assuming 1 g of tobacco per cigarette. To account for heterogeneity in smoked tobacco products, we use a standard unit of cigarette-equivalents of tobacco. Among former smokers, we estimated the distribution of the number of years since cessation. Among current smokers, we estimated two distributions: cross-sectional cigarette-equivalents of tobacco per smoker per day and cumulative pack-years across their lifetime. To incorporate these differences in risk in our estimation framework, we modelled continuous exposure distributions among both current and former smokers. These changes improve the reliability of estimates, particularly in low-income and middle-income countries, allow for disaggregation of disease burden by intensity of exposure, and also generate a multitude of new inputs that can be used by researchers and decision makers to inform and improve modelling studies.Įstimates of prevalence of current and former smoking tobacco use define the full population at risk, but risk of disease varies within these groups on the basis of intensity of smoking and length of time since cessation. We estimated new continuous exposure distributions, including distributions of age of initiation, cigarette-equivalents of tobacco smoked per day, pack-years, and years since cessation, and new cause-specific dose-response relative risk curves among both current and former smokers. In terms of methods, we developed and implemented a new unified approach to estimating the disease burden attributable to smoking tobacco use that addresses limitations of previous methods with direct estimation for all 36 causally linked health outcomes and reflecting dose-response associations among both current and former smokers. Compared with the GBD 2015 smoking prevalence and disease burden study, we have included more than 800 additional data sources on prevalence of smoking. This study, which is based on results from GBD 2019, updates and improves on previous estimates of the prevalence of smoking tobacco use and attributable disease burden. The Lancet Regional Health – Western Pacific.The Lancet Regional Health – Southeast Asia.The Lancet Gastroenterology & Hepatology.
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