Adam Briggs: “Sin taxes”—the language is wrong, but the evidence is clear

Boris Johnson has pledged to review the sugar levy on fizzy drinks if he becomes PM, but all that would prove is that the policy is right

Last week Boris Johnson suggested that a good way to revamp politics after Brexit would be to base “tax policy on clear evidence.”

He was referring to what he describes as “stealth sin taxes”—taxes on unhealthy food and drink currently exemplified by the soft drink industry levy—and pledged a review into their effectiveness. Aside from any of the potential politics or conflicts of interest underlying these claims, sugary drink taxes are an important piece of any evidence based public health policy.

We all know about the obesity crisis: over a third of 10-11 year olds and two thirds of adults in England are overweight or obese, at an estimated cost to the NHS of £6bn (€6.67bn; $7.47bn) in 2014. Reversing this crisis is hugely challenging. Crudely speaking, weight gain is caused by eating too much and moving too little, but our diet and activity levels are heavily influenced by social, environmental, and economic conditions, as well as the interplay between these and our genetics and our physical and mental health. Hence, my colleagues at the Health Foundation have called for cross government action and investment on the wider determinants that influence our health. This all amounts to a complex problem with no single, over-riding cause. And it needs a complex solution—a key part of which should be a soft drink tax, the evidence suggests.

So, why target just soft drinks? For a start, nearly all of us eat too much sugar, and drinks play a key role, particularly in children. Teenagers consume nearly three times their recommended amount of “free” sugar—any added sugar, including in juice or syrup—over a fifth of which comes from soft drinks.

These drinks are also associated with a range of poor health outcomes, having no nutritional benefit beyond their calories. Randomised controlled trials have shown how they can lead to weight gain in adults and children, and increasing numbers of studies associate them with diabetes, tooth decay, heart disease, and hypertension. On top of this, it makes sense to focus on soft drinks because the Treasury can easily define them, and the drinks that people would switch to are generally healthier.

Societal costs

Taxes are often used to correct “negative externalities”: the costly consequences of some products not borne in the original price but that are then “internalised” by a tax. For example, taxes on tobacco don’t just change behaviour—they internalise the health and societal costs of the resulting heart disease and cancers. The same is true of alcohol taxes and liver disease, and it also applies to soft drink taxes and obesity.

Over 30 countries have implemented some sort of soft drink tax, and “real world” data increasingly show their effects on consumers. Mexico has been particularly well studied with its peso-per-litre tax—a price increase of around 10%, resulting in an 8% reduction in purchases over the first two years. More recently, data from Philadelphia’s tax of 1.5 cents per ounce showed a 40% reduction in sales, and a meta-analysis of soft drink tax evaluations published just last month found that purchases fall by around 10% with a 10% price rise.

One of Johnson’s main concerns was whether these taxes “unduly hit those on lower incomes.” Here, he has a point: soft drink taxes—like National Insurance, VAT, or tobacco taxes—are regressive. People with less money pay a higher proportion of their income.

But evidence from a 2016 systematic review and the more recent Mexican data suggest greater levels of behaviour change, and therefore greater health benefits, among lower socioeconomic groups. Furthermore, population level interventions requiring lower levels of agency, such as taxes, are more effective and more equitable than interventions targeting the individual, such as gym or cookery classes. But, irrespective of these arguments, rather than scrapping a regressive tax aimed at improving population health, why not simply make the remaining tax system proportionately more progressive?

Public support

Taxes on sugary drinks are a key part of tackling obesity. They’ve been reviewed and supported by Public Health England, the Health Select Committee, the British Medical Association, and numerous medical royal colleges.

Johnson’s pledge is likely to have as much to do with ideology as a desire for more evidence (of which plenty is forthcoming, from the UK’s formal soft drink tax evaluation). The pledge has been cheered by some in his party and abhorred by others, but perhaps we needn’t be concerned. Soft drink taxes have public support: only last week a YouGov poll reported an approval rating of 55% for taxes on unhealthy food or drink, including 54% among Conservative voters.

Note that the poll referred to taxes on unhealthy food and drink, not to “sin taxes”: there’s nothing immoral about consuming soft drinks or chips. What may be immoral is stigmatising and labelling people who are overweight as sinners, while not supporting us all to stay healthy against a tide of environmental triggers for overconsumption.

So, in a week when the news is led by stories that obesity is now causing more cancers than smoking in four subtypes, I think that we can all get behind basing tax policy on clear evidence.


Adam Briggs is a public health specialty registrar based at the Health Foundation and an academic visitor at the Nuffield Department of Population, University of Oxford.

Competing interests: I have read and understood BMJ policy on declaration of interests and declare the following interests: I am a member of the UK Faculty of Public Health and past member of the UK Health Forum, both of which have position statements supporting a soft drink tax. I am a co-applicant on the NIHR funded five year evaluation of the UK Soft Drink Industry Levy. I have written various research and commissioned articles on soft drink taxes.