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Sugary soft drinks linked to raised risk of diabetes

‘One soft drink a day increases Type 2 diabetes risk by a fifth,’ The Independent warns, reporting on a European study that has examined the relationship between type 2 diabetes and sugary drinks.

The study – one of the largest of its kind – found strong links between sugary drink consumption and an increase in a person’s risk of developing type 2 diabetes. It attempted to assess the potential effects of various soft drinks on diabetes risk, including:

  • sugar-sweetened drinks, such as cola
  • artificially sweetened drinks, such as diet cola
  • fruit juices and nectars (diluted fruit juices that may contain sugar or sweeteners)

The researchers found that people who drank sugar-sweetened drinks were at a higher risk of developing type 2 diabetes. For every additional regular can-sized, sugar-sweetened drink per day, there was an 18% risk of developing the disease. However, drinking artificially sweetened drinks, juices and nectars was not associated with any increased risk.

While this type of research cannot prove a definite cause and effect between sugary drink consumption and diabetes, it does suggest a strong association. As most popular soft drinks now come in a sugar-free alternative, they would certainly seem to be the healthier choice. But a glass of tap water is both healthier and a lot cheaper.

Where did the story come from?

The study was carried out by researchers from Imperial College London and colleagues from eight European countries, and was funded by the European Union.

It was published in the peer-reviewed Diabetologia, the journal of the European Association for the Study of Diabetes, and is freely available to download on an open access basis.

The study was generally covered well by the papers that reported on it. However, many papers reported the increased risk of developing diabetes from drinking sugary drinks as being 22%, which to be fair was included in the press release about the study. The actual risk increase after adjusting for factors such as BMI was 18%.

The Daily Mail also included comments from a spokeswoman for the British Soft Drinks Federation, who sensibly advised that, like most things, soft drinks should be consumed in moderation.

What kind of research was this?

This was a case-cohort study in which researchers used data from a large study looking at how lifestyle and genetic factors interact to increase the risk of developing diabetes. Participants in the study were drawn from the UK, Germany, Denmark, Italy, Spain, Sweden, France and the Netherlands.

The study aimed to evaluate the association between the consumption of sweet drinks (juices and nectars, sugar-sweetened soft drinks and artificially sweetened soft drinks) and type 2 diabetes in European adults.

The authors point out that the consumption of sugar-sweetened drinks has been associated with an increase in the incidence of type 2 diabetes, but previous research has largely been in US populations. This means that the same association may not necessarily apply to Europe.

Consumption of sugar-sweetened drinks, they point out, may lead to type 2 diabetes because of its effect on weight gain. These drinks also have a ‘glycaemic effect’ that can lead to rapid spikes in blood glucose, as well as disturbances to the hormone insulin, which normally regulates blood sugar.

The association between diabetes and other types of soft drinks, such as fruit juice and artificially sweetened drinks, is less clear.

What did the research involve?

From the larger study (of 330,234 people), researchers selected 12,403 people who developed type 2 diabetes during the approximately 16 years of the study. Anyone who had existing diabetes at the start of the study was excluded from this group.

A diagnosis of type 2 diabetes was ascertained at each study centre in several ways, including through patients self-reporting and linking to GP and hospital registers, hospital admissions and mortality data. For most countries, researchers sought further evidence for the development of diabetes from a minimum of two independent sources, including independent medical record reviews.

The researchers randomly selected a subgroup of 16,154 individuals from the same study (including 778 who developed diabetes during follow-up) to act as a comparison group. The final sample size was 11,684 type 2 diabetes cases and a subgroup of 15,734 (including 730 diabetes cases).

Both groups had completed dietary questionnaires at baseline assessment, including information about their consumption of soft drinks. For most countries, these were divided into:

  • sugar-sweetened soft drinks
  • artificially sweetened drinks and juices (100% fruit or vegetables, or concentrates)
  • nectars (fruit juices with up to 20% added sugar)

Researchers say there was little standardised information from the different European centres on the distinction between fresh and concentrated fruit juices, or between fruit juices and nectars. These categories were therefore studied in combination. They also excluded Italy, Spain and Sweden from their analyses because data from these countries did not distinguish between the different types of soft drinks.

Sweet drinks were divided into the following categories of average consumption:

  • less than one glass a month
  • between one and four glasses a month
  • more than one to six glasses a week
  • one glass a day or more

One glass was equivalent to 250g, the standard serving used in the dietary questionnaire.

Participants also completed questionnaires on other factors that could influence results (confounders), including smoking, alcohol, physical activity and educational level. Body weight and height were measured to calculate body mass index (BMI) and participants were categorised into normal weight, overweight and obese.

Most centres also collected information on any history of chronic conditions, such as high blood pressure, high cholesterol, previous cardiovascular disease, and family history of diabetes.

The researchers used standard statistical methods to analyse the association between soft drink consumption and diabetes. They then adjusted their results for confounders such as lifestyle factors and BMI.

What were the basic results?

They found that one 336g (12oz) daily increment in sugar-sweetened and artificially sweetened soft drink consumption was associated with a 22% increase in risk of type 2 diabetes (hazard ratio (HR) 1.22, 95% confidence interval (CI) 1.09 to 1.38) and 1.52 (95% CI 1.26 to 1.83), respectively. An incremental risk applies to someone who had one drink (compared with someone who had none), or someone who had two drinks (compared with someone who had one), and so on.

After adjusting for energy intake and BMI, there was still an association between sugar-sweetened soft drinks and type 2 diabetes (HR 1.18, 95% CI 1.06 to 1.32), but the association with artificially sweetened soft drinks was not statistically significant (HR 1.11, 95% CI 0.95 to 1.31).

The participants’ juice and nectar consumption was not associated with type 2 diabetes incidence.

How did the researchers interpret the results?

The researchers say the study corroborates previous research on the association between increased incidence of type 2 diabetes and the high consumption of sugar-sweetened soft drinks in European adults, independent of their BMI.

Conclusion

This is a large, well-designed European study that appears to confirm the health risks of regularly consuming soft drinks. However, this study did have some limitations:

  • Dietary assessments were carried out only once, at the start of the study, so it did not take account of any changes in people’s consumption of soft drinks over the years.
  • Consumption of soft drinks was self-reported, which introduces the possibility of error.
  • The definition of juices and nectars included drinks both with and without added sugar. As the authors point out, the lack of any association between this category and diabetes should be interpreted with caution.
  • The study cannot establish whether the consumption of sugary drinks causes diabetes. Its results may have been affected by various other factors (called confounders), although researchers tried to take account of these.

It’s important to stay well hydrated, especially in warmer weather, but water is the healthiest choice for quenching your thirst. Or, if you can’t do without soft drinks, there is almost always a sugar-free alternative.

 

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