Public health researchers, advocates and policy makers have increasingly proposed taxes on sugar sweetened drinks as a way to reverse the rising consumption of such drinks – a trend believed to be a major contributor to the global obesity epidemic. In a recent research paper in the BMJ (doi:10.1136/bmj.f6189), Briggs and colleagues from Oxford have modelled the expected impact of such a tax on energy intake and the prevalence of obesity and overweight.

According to recent national data from the US, 12-19-year-olds consumed an average of 1,260kJ per day (301 calories) in sugar sweetened drinks. Adults over 20 years consumed 850kJ per day. Consumption is lower in the UK – 448kJ per day for 4-18-year-olds and 682kJ per day for 19-64-year-olds in one survey – but still substantial. In response, several European countries, including Hungary, Finland and France, have recently levied or increased existing taxes on these drinks. In the US, 34 states and the District of Columbia have food taxes that affect sugar sweetened drinks; 23 of these have taxes specifically targeting these drinks.

The question remains: do these taxes have positive effects on public health? Even without an effect on consumption, a tax could raise much-needed public funds for a variety of health needs. Nevertheless, the success of such a tax should be defined by its effect on the consumption of sugary drinks, energy intake and, most importantly, rates of obesity and overweight. Briggs and colleagues’ article makes an important contribution to this topic. 

Using data from four nationally representative UK surveys of dietary purchases, the price of drinks, and body weight, they estimated that a 20% tax would lead to an average per capita reduction of 16.7kJ per day (95% credible interval, 11.3 to 21.7). This change is small but, were it to be applied across the entire UK population, the authors predict a 1.3% reduction in the prevalence of obesity, just over 180,000 people, with an additional reduction of 104,000 overweight people.

Not surprisingly, the reduction in energy intake from a tax would be greatest in those who consume the greatest number of sugar sweetened drinks: 16-29-year-olds (56.3kJ). People over the age of 50 years, who consume very few of these drinks, would have no significant change in energy intake. People on lower incomes would have slightly smaller reductions than those with higher incomes, partly because of their substitution of high-fat milk for sugar sweetened drinks.

This study provides evidence that a 20% tax on sugary drinks can work. The more pressing question is whether policy makers can implement a tax this high. Existing taxes in the US and Europe are low, typically far less than 10%. These low rates, although generating important revenue, have never been shown to alter obesity rates. Denmark, the one European country with a high tax, recently repealed it, citing concerns about citizens shopping for goods in neighbouring countries without a tax.

As is the usual conclusion to major public health question, more studies are needed and more countries to implement high taxes and measure the results, with careful evaluation of the impact on consumer behaviour.