Do sugary drinks cause type 2 diabetes?
Research might prompt new public health measures
Soft drinks, sodas, and fizzy pop are big business. In 2014, across the United Kingdom we downed 14.8 billion litres of sweetened beverages, growing the industry’s value to a sparkling £15.7bn (€22.4bn; $24.5bn). Yet despite their popularity, the health impact of sugar sweetened soft drinks has come under increasing scrutiny. Concern has focused chiefly on three potential adverse effects—obesity, type 2 diabetes, and tooth decay—with thousands of studies now reporting on associations with soft drink consumption. The potential link to type 2 diabetes was highlighted in July 2015 after publication of the most comprehensive meta-analysis of the subject to date.  Around 3.9 million people in the United Kingdom have diabetes and this figure is predicted to rise to 5 million by 2025, so there is immense public interest in establishing to what extent soft drinks might be contributing to this epidemic. Diabetes costs the NHS £10bn a year, or 10% of its budget, largely because of complications such as amputations, blindness, and kidney failure. 
What does the evidence say?
Published in The BMJ, this systematic review and meta-analysis pooled data from 17 cohorts of patients, comprising 38 253 people with type 2 diabetes and spanning 10 126 756 million person years. Soft drink consumption was assessed mainly by questionnaire or interview, with results analysed separately for sugar sweetened drinks, artificially sweetened drinks, and unsweetened fruit juices.
The researchers concluded that the relative risk of developing diabetes rose by 18% for each additional 250 mL of sugary drink a person consumed a day. This association remained even after adjustment for people with normal body weight, where the risk of developing diabetes rose by 13% for every extra sugary drink consumed daily compared with those who did not consume sugary drinks. Increased risks of diabetes were also found for artificially sweetened drinks—for example, diet, sugar-free or light versions, and fruit juices—but these findings were less robust because of variation and methodological flaws in the studies. Focusing on sugar sweetened drinks, the researchers calculated that current consumption could have caused around two million excess cases of diabetes in the United States and 80 000 in the UK over the past decade, with costs of nearly £12bn and £206m respectively.
The results are in line with several previous studies reporting that sugary drinks contribute to the development of diabetes. The state of the evidence was recently summed up in the Carbohydrates and Health report by the Scientific Advisory Committee on Nutrition (SACN), an independent expert group which advises the British government. This report, published five days before The BMJ study, stated among its conclusions: “Prospective cohort studies indicate that greater consumption of sugar-sweetened beverages is associated with increased risk of type 2 diabetes mellitus.” The SACN recommended that consumption of sugar sweetened beverages “should be minimised in children and adults” and that a person’s average “free sugars” intake should not exceed 5% of total dietary energy—half the previously recommended amount. Free sugars are those added to a drink or food by either the manufacturer or the consumer, including cane sugar, brown sugar, honey, fruit juice concentrate, corn syrup, fructose, glucose, sucrose, and others.
Reactions: who said what?
Both the SACN report and the meta-analysis have attracted a wide range of responses, which have increased pressure on the government, retailers, and soft drinks industry to take action on unhealthy drinks and food.
Fumiaki Imamura, lead author of the meta-analysis, told Student BMJ the best advice for the public was to reduce consumption of sugar sweetened beverages as much as possible. When pressed on what constituted a sensible number of sugary drinks to consume on a daily or weekly basis, he said: “Zero. Based on the best available evidence, we do not need to consume any.” Water, unsweetened coffee, and unsweetened tea seem the best alternatives for reducing the risk of type 2 diabetes, said Imamura, a senior investigator scientist at the University of Cambridge’s MRC Epidemiology Unit. Switching to diet drinks or fruit juice would not directly reduce diabetes risk but could still be beneficial for losing weight owing to their lower calorie content, he said.
Ian Macdonald, chairman of the SACN carbohydrates and health working group, said: ‘The evidence is stark—too much sugar is harmful to health and we all need to cut back. The clear and consistent link between a high sugar diet and conditions like obesity and type 2 diabetes is the wake-up call we need to rethink our diet.”
Others are pushing strongly for specific policy interventions to curb the nation’s sweet tooth. Simon Stevens, chief executive of NHS England, wants supermarkets to increase the price of junk food and unhealthy drinks and use the proceeds to increase the salaries of low paid workers. “There’s absolutely no reason why kids should have sugary, fizzy drinks. They are of no nutritional value, they are damaging to health and an entirely discretionary purchase,” he said. The BMA is meanwhile calling on the government to introduce a 20% tax on sugary drinks and use the extra revenue to subsidise fresh fruit and vegetables.
The soft drinks industry responded quickly to the SACN report. The British Soft Drinks Association said the committee had set “unrealistic targets” which “make little sense and will confuse people.” The association is also highlighting existing progress in the area, saying manufacturers have reduced sugar content by more than 8% since 2012. The Food and Drink Federation meanwhile says it is unhelpful to “demonise” one particular dietary ingredient and emphasises that “sugars can be enjoyed safely as part of a varied and balanced diet.” The federation’s director of regulation, Barbara Gallani, has also strongly criticised Imamura’s study, saying it contained “sweeping assumptions” about cause and effect which cannot be proved by observational studies. “Unfortunately, this strong caveat did not prevent the inclusion of a headline grabbing and highly speculative estimate on the number of diabetes cases that sugar sweetened soft drinks may give rise (and yet may not give rise!) to,” she wrote in a rapid response on thebmj.com.
All eyes will now be on the government for its response to the SACN report, whose recommendations have, if anything, been strengthened even further by Imamura and colleagues’ meta-analysis. Public Health England was also due to report to the Department of Health on measures to reduce the population’s sugar intake in the spring this year, but the report has not yet been released. Thus far, the government has steered clear of increased regulation or taxes for the sector, instead focusing its efforts on public education campaigns, promoting clearer labelling, and encouraging the food and drinks industry to reduce sugar and calorie contents voluntarily.
In terms of further research, it seems the association between sugar sweetened drinks and diabetes is as well established as it is ever likely to be. Imamura acknowledges that causality has not yet been comprehensively proved but says it is “biologically plausible” on the basis of what we know about the body’s response to high sugar loads. The studies required to definitively prove causality would be complex and extremely long, and their absence should not hold back the debate, he adds. With regard to artificially sweetened beverages and fruit juice, the jury remains out on whether they definitively cause diabetes and at what levels of consumption.
More research is certainly needed on which policy interventions will be most effective for reducing the UK’s sugary drinks consumption. Similar moves overseas have had mixed results: New York city attempted to introduce a portion size limit on sugary drinks in 2012 but saw this defeated in court after strong opposition from industry. Taxes have been introduced in some countries and are being debated in 22 US states, but so far only Washington State has passed such a law and even that was repealed the next year. Many other countries, including France, Japan, and Australia, have restricted sales of sugary drinks in schools, while France has also increased advertising restrictions for processed foods and drinks.
Moreover, soft drinks are just one contributor to the diabetes epidemic. Imamura’s population projections suggest they were responsible for at most 20% of diabetes cases in the UK over the past decade, suggesting many other preventive measures will be required.
A national debate on policy change looks imminent. It is likely that some public health intervention is required to reduce the population’s sugar consumption, but we don’t know how far this could go. It could be in the form of a sugar tax, which would increase the prices of sugary products and make them less attractive to the public. Or, it is more likely that we will see more incremental changes in product labelling or moves such as Tesco’s announcement to stop selling Ribena and Capri-Sun in their children’s juice category as part of their 10 point plan against obesity.
What to tell patients
In the meantime, medical students can follow the advice of the SACN and Public Health England and encourage patients to cut down on sugary drinks as much as possible, especially those at risk of developing diabetes. Diet drinks and unsweetened fruit juice typically contain fewer calories, which is good for losing weight, but it is unclear whether they increase the risk of diabetes. Students can get involved by writing to ministers, starting petitions, or even encouraging their hospitals and medical schools to stop selling sugary soft drinks, particularly in areas where patients who are at risk of developing type 2 diabetes might buy them.
What we know so far
- Drinking sugar sweetened soft drinks on a daily basis increases the risk of type 2 diabetes, regardless of body weight
- Artificially sweetened drinks and fruit juice might also increase the risk of developing diabetes, although there is uncertainty surrounding this
- Government agencies are looking at ways to reduce the UK’s consumption of sugary drinks, meaning changes in the law could be on the way
- Overseas attempts to regulate sugary drinks sales have been problematic. The UK government is likely to face fierce opposition from industry if it makes similar changes
1St George’s, University of London
Correspondence to: firstname.lastname@example.org
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.
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Cite this as: Student BMJ 2015;23:h4217