"Swapping orange squash for a cup of tea cuts diabetes risk," The Daily Telegraph reports.
This widely-reported news is based on a major UK study, involving around 25,000 adults, which looked at the association between drink choices and the risk of type 2 diabetes. It found that those who consumed more of their calories through sugary drinks, and those who drank more soft drinks or sweetened milk drinks, were more likely to develop type 2 diabetes.
The study has a number of strengths, including its large size and use of multiple approaches to identify people who developed diabetes. But its main limitation is that other factors may be contributing to the effect seen, even though the researchers did try to reduce this as much as possible.
Based on their data, the researchers estimated that swapping water or unsweetened tea or coffee for soft drinks or sweetened milks could potentially reduce the number of new diabetes cases by up to 25%.
Some sugary drinks contain a surprisingly high amount of calories – for example, a 330ml can of coke contains 139 calories, which would take around an hour of dog walking to burn off.
Reducing your calorie intake by swapping sugar-sweetened drinks for unsweetened drinks, such as tap water, could be one way to help achieve this goal.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge, and was funded by The Medical Research Council UK and Cancer Research UK.
It was published in the peer-reviewed medical journal Diabetologia.
The UK media's coverage of the study was accurate.
What kind of research was this?
This was an ongoing prospective cohort study called the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk study.
The current analysis looked at whether the amount of sugar-sweetened beverages (SSBs), artificially sweetened beverages (ASBs) and fruit juice a person drank was linked to their risk of developing type 2 diabetes. The researchers also wanted to estimate what impact swapping non-sweetened beverages for these sweet beverages would have.
A previous statistical pooling of prospective studies found that higher SSB consumption was associated with greater diabetes risk, while studies have had varying findings for ASBs and fruit juice.
However, the researchers note that these studies have largely relied on food frequency questionnaires, which do not collect very detailed information on drinks. They wanted to use food diaries (where people are asked to record their food consumption on a daily basis) in their study to better assess drinks intake.
This is the best way to assess this question, given that it would be unethical to randomly assign people to drink a lot of sugary drinks over a long period of time.
The main limitation of this type of study is that healthy (and unhealthy) behaviours and environments tend to cluster together, so picking apart their effects is difficult.
What did the research involve?
The researchers recruited adults in the UK who did not have diabetes and had them record their food and drink consumption over a week.
They then followed them up over almost 11 years to see who developed type 2 diabetes, and analysed whether people who drank more sweet beverages were at increased risk.
Using their results, they then calculated what impact it would have if people swapped non-sweetened drinks, such as water, for these sweet beverages.
The 25,639 participants in the study were recruited in the 1990s, when they were aged 40 to 79 years old. They filled out a food diary for a week, and the researchers used these to determine how much of the following they drank:
- soft drinks – squashes and juice-based drinks sweetened with sugar
- sweetened tea or coffee
- sweetened milk beverages – such as milkshakes, flavoured milks, and hot chocolate
- artificially sweetened drinks (ASBs) – such as diet sodas
- fruit juice
The first three categories were classed as SSBs. The participants also provided other information on their lifestyles. During the study, they had health checks and filled in follow-up health and lifestyle questionnaires.
The researchers followed participants up until 2006, and identified anyone who developed type 2 diabetes through the health checks, questionnaires, and medical records. If a person reported they had diabetes but this could not be confirmed with medical records, they were not counted as having the condition.
The analyses included the 24,653 participants who did not have diabetes or a family history of diabetes and had reported all the information the researchers needed. The researchers looked at whether the number of servings of the individual drinks consumed was linked to the risk of developing type 2 diabetes during the study.
These analyses took into account a range of factors that could influence the results (potential confounders), such as:
- socioeconomic status
- physical activity
- intake of other sweet beverages
- total calorie intake
- body mass index (BMI)
- waist circumference
The researchers used standard methods to estimate what impact it would have if people stopped consuming SSBs, based on their findings. They also calculated the potential impact of swapping water or ASBs for SSBs.
What were the basic results?
During the study, 847 participants (3.4%) developed type 2 diabetes.
After adjustment for all of the potential confounders, including total energy intake and BMI:
- each additional serving of soft drinks was associated with a 14% increase in the risk of developing diabetes (hazard ratio [HR] 1.14, 95% confidence interval [CI] 1.01 to 1.32)
- each additional serving of sweetened milk drinks was associated with a 27% increase in the risk of developing diabetes (HR 1.27, 95% CI 1.09 to 1.48)
- sugar-sweetened tea and coffee, ASBs, fruit juice and water were not associated with type 2 diabetes risk
Overall, consuming more sweet drinks (measured as what percentage of a person's calorie intake came from these drinks) was associated with increased type 2 diabetes risk.
Substituting one serving a day of water or unsweetened tea or coffee for soft drinks or sweetened milk drinks was estimated to have the potential to reduce the number of new cases of type 2 diabetes by 14-25%. Substituting ASBs for SSBs was not estimated to have a significant effect.
If people who drank sweet beverages reduced their intake of these drinks so they accounted for less than 2% of their total calorie intake, this was estimated to have the potential to prevent 15% of new diabetes cases.
How did the researchers interpret the results?
The researchers concluded that, "The consumption of soft drinks, sweetened milk beverages and energy from total sweet beverages was associated with higher type 2 diabetes risk independently of adiposity [BMI and waist circumference]".
They suggest that, "Water or unsweetened tea/coffee appear to be suitable alternatives to SSBs for diabetes prevention", and feel their findings are of public health importance.
This cohort study has found an association between sugar-sweetened drink consumption and the risk of type 2 diabetes. It estimated that swapping water or unsweetened tea or coffee for these beverages could have the potential to reduce the number of new diabetes cases by up to 25%.
The study has a number of strengths, including its large size and prospective collection of data. It also used multiple approaches to identify people who developed diabetes, which should help to make sure that most, if not all, cases were identified.
People also used a food diary to record food and drink intake, which is reported to provide more detailed information than the questionnaire-based methods used in many previous studies.
As with all studies of this type, the main limitation is that it is difficult to single out the impact of one factor and be sure that no others are contributing to the link seen.
For example, people who drank more sweetened tea or coffee and sweetened milk beverages tended to have less healthy diets overall.
The researchers did take into account a range of factors, such as diet and physical activity in their analyses, to reduce this as much as they could, but it could still be having some effect.
Another limitation is that the researchers only assessed drink intake once, at the start of the study, and this may have changed over time.
The figures for the percentage of cases of type 2 diabetes that could be prevented are estimates. They are based on the assumption that the risk factor (sugar-sweetened drinks in this case) is directly causing the entire link seen, which may not be the case.
This method can overestimate the impact of individual factors. However, these types of estimates are used to help public health policy makers decide which disease risk factors are most important for them to target.
Overall, we know that being overweight or obese is a major risk factor for type 2 diabetes. Maintaining a healthy weight will help to reduce this risk.
Reducing your calorie intake by swapping sugar-sweetened drinks for unsweetened drinks could work towards this goal. And given that UK tap water is cheap, calorie-free and safe to drink, it would seem the obvious choice for a sugar swap.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Guardian, 30 April 2015
The Daily Telegraph, 30 April 2015
Mail Online, 1 May 2015
Daily Express, 1 May 2015
Links to the science
Diabetologia. Published online April 30 2015