Changes in household purchasing of soft drinks following the UK Soft Drinks Industry Levy by household income and composition: controlled interrupted time series analysis, March 2014 to November 2019
Authors: Rogers Nina T. , Cummins Steven , Pell David , Rutter Harry , Sharp Stephen J. , Smith Richard , White Martin , Adams Jean 
Published: November 2023

Objectives

To examine changes in volume of and amount of sugar in purchases of soft drinks according to household income and composition, at 19 months following the implementation of the UK Soft drinks industry levy (SDIL).

Design

Controlled interrupted time series analysis

Setting

Representative households (mean weekly number of households =21,908) across Great Britain

Participants

Members of the Kantar Fast Moving Consumer Goods panel, a market research panel which collects data on weekly household purchases (eg: drinks, confectionery etc) between March 2014 to November 2019.

Interventions

The SDIL, is a two-tiered tax (announced in March 2016 and implemented in April 2018) on manufacturers of soft drinks. Drinks containing ≥8g sugar /100mls and ≥5 to <8g sugar/ 100mls are taxed at £0.24/litre and £0.18/litre, respectively. Soft drinks containing < 5g sugar/100ml are not subject to the levy. Levy exempt drinks, irrespective of sugar content, include milk and milk-based drinks, no-added-sugar fruit juice and powder used to make drinks.

Main Outcome measures

Absolute and relative differences in the volume of and amount of sugar in non-alcoholic soft drinks, confectionery and alcohol purchased weekly by household income (<£20,000, £20-50,000 or >£50,000) and composition (presence of children [<16years] in the household (yes or no), 19 months after SDIL-implementation, compared to the counterfactual scenario based on pre-announcement trends and using a control group (toiletries).

Results

By November 2019, overall purchased weekly sugar in soft drinks fell by 7.46g (95%CI: 12.05, 2.87) per household but volumes of drinks purchased remained unchanged, compared to the counterfactual based on pre-announcement trends. In low-income households, weekly sugar purchased in soft drinks decreased by 14.0% (95%CI: 12.1,15.9) compared to the counterfactual but in high income households increased by 3.4% (1.07,5.75). Similarly, among households with children, sugar purchased decreased by 13.7% (12.1, 15.3) compared to the counterfactual but increased in households without children by 5.0% (3.0,7.0). Low-income households and those with children also reduced their weekly volume of soft drinks purchased by 5.7% (3.7, 7.7) and 8.5% (6.8, 10.2) respectively. There was no evidence of substitution to confectionary or alcohol.

Conclusion

In the second year following implementation of the SDIL, there were sustained reductions in sugar derived from soft drink purchases, but no change in volume of soft drinks purchased. Effects on sugar purchased were greatest in those with the highest pre-SDIL purchasing levels (low-income households and those with children). The SDIL may contribute to reducing dietary inequalities.

Trial registration:ISRCTN18042742.

Summary box

What is already known on this topic

The World Health Organization recommends taxes on sugar sweetened beverages (SSBs) to improve population health; systematic reviews indicate these can successfully reduce population purchasing and consumption; differential impacts across demographic groups have been less studied.

In the UK, SSB intake is highest in lower socioeconomic groups and children.

The UK soft drinks industry levy (SDIL) successfully reduced household purchasing of sugary from soft drinks by a mean of 8.0g per household per week at one year; longer term and differential effects of across different demographic groups have not been studied.

What this study adds

19 months following implementation of the SDIL, there were sustained reductions in sugar from purchased soft drinks of 7.5g per household per week, but no change in the volume of purchases suggesting the SDIL may lead to long-term health gains without harming industry.

Households with the lowest incomes (<£20,000/year) had the largest reductions in purchases of sugar from soft drinks which (compared to pre-announcement trends), dropped by an average of 70g of sugar per household per week, equivalent to just over two 250ml servings of a drink containing 5g sugar per 100 ml per person per week; households with children living in them reduced their purchasing of sugar from soft drinks by 56g per household per week.

The SDIL may contribute to reducing existing inequalities in dietary intake.