The UK Treasury's Soft Drinks Industry Levy (SDIL) is being put through a comprehensive health check, with researchers tracking its effects on everything from supermarket prices and product recipes to children's weight and hospital visits for rotten teeth. This matters because the levy—a tax on sugary drinks—was designed to tackle rising obesity and dental decay, but its real-world impact remains unclear. Previous studies have looked at isolated outcomes, but this evaluation connects the dots between industry reformulation, consumer purchasing, and actual health changes across the population. If successful, this research will reveal whether the tax is working as intended and for whom. It could show that reformulation reduced sugar intake without pushing people toward other unhealthy products, or that the benefits are concentrated in wealthier households while lower-income groups see less improvement. The findings will inform future tax policy, helping the Treasury and public health officials decide whether to adjust the levy or extend it to other products. The economic modelling will also show whether the tax saves the NHS money by preventing diabetes, heart disease, and cancers, or whether unintended consequences—like job losses or increased household spending on other goods—offset those gains.
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We will conduct a natural experimental evaluation of proximal, intermediate & distal outcomes (work package (WP) 1), micro & macro-economic evaluation (WP3), & qualitative process evaluation (WP4) over 3 2-year time periods (2014-20). Simulation modelling of health & economic outcomes will focus on longer time horizons (WP2). In WP5, findings from WP1-4 will be synthesised and interpreted to refine intervention theory, and stakeholders engaged in dissemination. WP1 – will use interrupted time series & regression analyses to evaluate impacts of the SDIL on: 1. Soft drink product diversification, formulation & price by brand, category & product size (volume) using data from 6 leading supermarket chains 2. Purchases of SSBs, all other drinks, confectionary & toiletries overall & by age, sex & socio-economic position (SEP), using household purchasing data from Kantar World Panel 3. Consumption of SSBs & confectionary overall & by age, sex & SEP using data from the National Diet & Nutrition Survey 4. Prevalence of childhood obesity using data from the National Child Measurement Programme & hospital admissions for severe dental caries using data from Hospital Episode Statistics (HES) overall & by age, sex & SEP. WP2 – will adapt an existing life table model (PRIMEtime) for proportional multistate life table analyses. Data from WP1 will be used to estimate the effect sizes for SSB consumption & free sugars from drinks. We will estimate the impact of these changes on health outcomes over the short (5 years), medium (5-10 years) & long term (>10 years). Disease outcomes of interest will include dental caries, T2DM, cardiovascular & kidney disease, & obesity-related cancers (e.g. colon, kidney, liver, breast & pancreas). WP3 – will involve: (i) a micro-economic evaluation, modelling (using PRIMEtime) the health & social care cost impacts & health outcomes (QALYs gained); & (ii) a macro-economic evaluation, to assess the wider impacts of SDIL on industry, households, Treasury and UK economy. In (i) NHS costs will be estimated using programme-budgeting & HES data. Social care & wider societal costs will be assessed overall & by age, sex, utility score & ICD10 codes. Data on dental caries & associated health care costs will be incorporated & we will extend the cost estimates to cover children & adolescents. In (ii) we will use a Computable General Equilibrium (CGE) model of the whole economy that includes the cost minimising & profit maximising behaviour of producers, consumption & saving behaviour of households & government, taxation mechanisms & the use of labour, capital & other factors in order to produce goods & services for investment or consumption, & includes trade across international borders. WP4 – will use qualitative methods to determine the perceived acceptability & impacts of the SDIL. We will conduct thematic Framework analysis of interviews with professionals & focus groups with the public, thematic content analysis of newspapers articles & social media (twitter) output & analysis of survey questions on consumer attitudes to SSBs collected by Kantar in their household purchasing panel. WP5 – will involve synthesis of the findings from WPs1-4 using our systems map & refinement of intervention theory. Triangulation of evidence generated using different methods from WPs1-4 will facilitate corroboration of findings, supported by techniques such as pattern matching. We will engage stakeholders in dissemination.
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