Sweetened beverage taxes and changes in beverage price, imports and manufacturing: interrupted time series analysis in a middle-income country

BACKGROUND: The Pacific Island nation of Tonga (a middle-income country) introduced a sweetened beverage tax of T$0.50/L in 2013, with this increasing further in 2016 (to T$1.00/L), and in 2017 (T$1.50/L; US$0.02/oz). Given the potential importance of such types of fiscal intervention for preventing chronic disease, we aimed to evaluate the impact of these tax changes in Tonga. METHODS: Interrupted time series analysis was used to examine monthly import volumes and quarterly price and manufacturing 1 year after each tax change, compared with a counterfactual based on existing trends. Autocorrelation was adjusted for when present, and adjustments were made for changes in GDP per capita, visitor numbers, season and T$/US$ exchange rate. RESULTS: In the year after the 2013, 2016 and 2017 tax increases, the price of an indicator soft drink increased by 16.8% (95%CI: 6.3 to 29.6), 3.7% (− 0.6 to 8.3) and 17.6% (6.0 to 32.0) respectively. Imports of sweetened beverages decreased with changes of − 10.4% (− 23.6 to 9.0), − 30.3% (− 38.8 to − 20.5) and − 62.5% (− 73.1 to − 43.4) respectively. Juice imports changed by − 54.2% (− 93.2 to − 1.1), and sachet drinks by − 15.5% (− 67.8 to 88.3) after the 2017 tax increase. Tonga water bottling (T$) increased in value by 143% (69 to 334) after the 2016 tax increase and soft drink manufacturing increased by 20% (2 to 46, albeit 5% market share). CONCLUSIONS: Consistent with international evaluations of sugar-sweetened beverage taxes, the taxes in Tonga were associated with increased prices, decreased taxed beverages imports, and increased locally bottled water.