When our Minister of Health and Prime Minister say they're waiting for definitive evidence on the health benefits of a sugary drinks tax before deciding whether to follow the United Kingdom's lead, they know they are on safe ground.

That's because 'definitive evidence' on the health benefits of national taxes is unobtainable.

Actually definitive evidence on almost any health intervention is unobtainable. Moreover, politicians don't usually wait for definitive evidence before making decisions. None of the 22 strategies in their new childhood obesity plan are based on evidence that is as good as the evidence for a sugary drinks tax. So why wait now, when the best available evidence indicates that the benefits are likely to be substantial and when failure to address the obesity and diabetes epidemics are likely to be disastrous?

Internationally, those opposed to cigarette taxes - the tobacco companies, some addicted smokers, and politicians in the pocket of the tobacco industry - still argue that there is no definitive evidence on the benefits of tobacco taxes, despite every public health agency in every developed country supporting tobacco taxes.

Millions of lives were lost unnecessarily because politicians used this excuse to sit on their hands for years before introducing tobacco taxes. We don't want to make the same mistake with sugar, given that over 300,000 New Zealanders have diabetes, over one million are obese and almost half of kiwi kids have tooth decay.


To definitively demonstrate the benefits of a sugary drinks tax one would need to randomly assign multiple countries to either introducing a tax or not while making sure all other factors that could increase or decrease obesity and diabetes in all countries studied remained identical. Then one would need to measure changes in the prevalence of obesity on large numbers of representative samples from each population over a period of years. This could definitively prove that the introduction of a tax was linked to favourable trends in obesity. But even if this were possible, it's never difficult to find some flaw in the evidence as no study is perfect.

So then the defence against introducing a tax would be that 'the experts don't agree.'

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When George Osborne, the UK Chancellor of the Exchequer, introduced his new sugary drinks tax last week he cited the fact that 'five-year-old children are consuming their bodyweight in sugar every year, and experts predict that within a generation more than half of all boys and 70 per cent of girls could be overweight or obese. He said: "I am not prepared to look back at my time here in this Parliament, doing this job and say to my children's generation 'I'm sorry. We knew there was a problem with sugary drinks. We knew it caused disease. But we ducked the difficult decisions and we did nothing'."

Osborne knew that definitive evidence of health benefits was unobtainable. Instead he weighed up the likely benefits, based on the best evidence available, against the likely harms. Of course the only definitive harms would be to the pockets of companies wanting to sell more and more sugar-laden products and to the sensibilities of those whose ideological views on taxes or regulations outweigh their concerns for the millions of British people with obesity and diabetes.

Mr Osborne would have asked his health advisors the key question: 'could a sugar tax do more harm than good to the huge numbers of people with obesity and diabetes?' The answer of course is a definitive no.

There is a famous and obscene quote from a tobacco executive in the 1960s that goes: 'We don't smoke this shit, we just sell it. We reserve the right to smoke, for the young, the poor, the black and the stupid.' I don't for an instance believe that people who consume too much sugar are stupid, but they tend to be young, they tend to be poor (because high sugar foods and drinks are the cheapest calories available) and Māori and Pacific peoples have higher levels of obesity and diabetes than almost anyone else in the world.

A sugary drinks tax alone won't reverse New Zealand's 'diabesity' epidemic or cure tooth decay but the best available evidence suggests it will be one of the most effective strategies.


Those of us committed to improving the health of current and future generations of kiwis need all the help we can get. So please Mr Key and Dr Coleman, don't wait for the unobtainable definitive evidence. Act on the best available evidence, like Mr Osborne just did in Britain.

Rod Jackson is Professor of Epidemiology at the School of Population Health, University of Auckland.
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