"Drinking more than two sugary or artificially sweetened soft drinks per day greatly increases the risk of diabetes, research has shown," The Guardian reports.
The research was a Swedish cohort study of sweetened drink consumption over the past year for people diagnosed with type 2 diabetes. They also looked at people with an uncommon form of diabetes known as latent autoimmune diabetes in adults (LADA) which shares features with type 1 and 2 diabetes.
Both groups were then compared with a diabetes-free control group.
Drinking more than two sweetened drinks per day was linked with being roughly twice as likely to have diabetes.
For type 2 diabetes the link was similar when separately analysing sugary and diet drinks. The link with LADA was a little weaker and did not stand up to statistical significance when separately analysing sugary and artificially-sweetened drinks.
However, this study cannot prove that sweetened drinks alone have directly caused these conditions. Other unhealthy lifestyle factors like smoking and poor diet in general were also linked with the two forms of diabetes.
Also, one of the hallmark symptoms of diabetes is increased thirst so it could be possible that in some cases the diabetes came first and was then followed by increased consumption of sweetened drinks.
These uncertainties aside, the results broadly support our understanding of the risk factors for diabetes, which also apply to several other chronic diseases.
Read more about diabetes prevention.
Where did the story come from?
The study was carried out by researchers from the Karolinska Institutet, Stockholm and other institutions in Sweden and Finland. Funding was provided by the Swedish Research Council, the Swedish Research Council for Health, Working Life and Welfare, AFA Insurance and the Swedish Diabetes Association.
The UK media gives slightly confused reporting by dividing between reporting on diet drinks or sugary drinks.
All the media reports mentioned two drinks per day. The significant links were actually for more than two drinks per day – for example, two-and-a-half or three.
There were no links for two or fewer drinks of any type. In any case, with food frequency questions there is the chance that estimates on portion size or frequency may be inaccurate.
What kind of research was this?
This was a case-control study within a population-based Swedish cohort study that aimed to see whether consumption of sweetened drinks was associated with risk of a rare form of diabetes called latent autoimmune diabetes in adults (LADA).
LADA has features of type 1 diabetes, where the body's own immune cells destroy the insulin-producing cells in the pancreas. But unlike type 1 diabetes, which normally develops in childhood, in LADA the cell destruction is much slower.
Also, the condition often develops later in life and shares many features with type 2 diabetes. For example, the person doesn't always need treatment with insulin straight away. This study reports that in the Swedish diabetes registry, LADA accounts for 5% of all cases.
The researchers compared drink consumption between cases with LADA or conventional type 2 diabetes and diabetes-free controls. The difficulty with this study design is that it's always going to be difficult to prove that a single factor, such as sweetened drinks, is definitely the cause of the condition.
What did the research involve?
The study used data from the population-based cohort study ESTRID (Epidemiological Study of Risk Factors for LADA and Type 2 Diabetes) which started in 2010.
This study invited people with LADA or Type 2 diabetes from the Swedish diabetes registry to take part, along with a random selection of people aged 35 or over who were free from diabetes to act as controls.
Participants were set to be recruited in a ratio of four people with type 2 diabetes and six controls for every one person with LADA.
All people with diabetes were diagnosed by a doctor. There are said to be no definite criteria for LADA diagnosis, but the study used criteria in line with other literature.
Participants completed a health and lifestyle questionnaire. This included information on weight and height, physical activity, smoking, alcohol intake, family history of diabetes and educational level.
These factors were considered as potential confounders.
They also completed a 132-item food frequency questionnaire. Participants were asked to report their normal food consumption in the preceding year. Three questions asked about intake of sweetened drinks:
- diet cola
- other diet soft drinks/soda (for example diluted syrups)
They were asked to report the number of 200ml servings per day or per week. Questions on fruit juice weren't analysed in the study.
The researchers analysed the difference in sweetened drink consumption between cases and controls, adjusting for the other confounders.
What were the basic results?
Data was available for 1,136 people with type 2 diabetes, 357 people with LADA, and 1,371 diabetes-free controls.
Average age was 59 for people with LADA and controls, and 68 for those with type 2 diabetes.
Just under two-thirds of all people reported consuming sweetened (including artificially sweetened) drinks.
In general they found that consumption of sweetened drinks was linked with higher body mass index (BMI) and other poor lifestyle factors like smoking, low physical activity and consumption of processed meat and sugary foods.
In adjusted analyses, people drinking more than two servings of any sweetened drinks a day had almost doubled odds of LADA compared with non-consumers (odds ratio [OR] 1.99, 95% confidence interval [CI] 1.11 to 3.56). Each extra daily serving was linked with 15% increased risk (OR 1.15, 95% CI 1.02 to 1.29).
For type 2 diabetes, the link was a little stronger. More than two servings a day was linked with more than twice the odds of type 2 compared with non-consumers (OR 2.39, 95% CI 1.39 to 4.09), and each extra daily serving conferred a 20% increased risk (OR 1.20, 95% CI 1.07 to 1.34).
When separately analysing both sugar-sweetened and artificially-sweetened drinks, the findings were similar and still significant for type 2 diabetes. However, for LADA all links fell short of statistical significance on separate analysis.
Drinking two or fewer drinks per day – either sugar-sweetened or artificially-sweetened drinks – was not linked with either LADA or type 2 diabetes.
How did the researchers interpret the results?
The researchers conclude: "High intake of sweetened beverages was associated with increased risk of LADA. The observed relationship resembled that with type 2 diabetes, suggesting common pathways possibly involving insulin resistance."
This study primarily aimed to see if consuming sweetened drinks was associated with the rarer condition of LADA, as it is with type 2 diabetes.
The researchers found that having more than two drinks per day was linked with increased odds of both conditions – though the link with LADA was a little weaker and not statistically significant when separately analysing diet and sugary drinks.
They also found that high BMI and other poor lifestyle choices were also linked with the conditions.
The findings generally support what is understood about type 2 diabetes, that high sugar intake, poor diet, low activity and high BMI increase risk. They similarly show that this is also likely to be the case with this rarer variant of the condition.
There are a couple of points to note:
- This study design cannot prove that sweetened drinks are the direct cause of diabetes in these people. It is likely that high consumption of sweetened drinks is part of a wider picture of generally poor lifestyle habits. Though the researchers have adjusted their analyses for confounding factors, it is difficult to fully account for each health and lifestyle variable that could be having an influence.
- The results are based on a food frequency questionnaire assessing intake over the past year. Though this is the best way you can look at this, it may not be entirely accurate – particularly when questioning regular portion size – or reflect longer term patterns over the course of the person's lifetime.
- Several of these analyses deal with small numbers. For example, only 14 people with LADA drank more than two servings of diet drinks a day. Analyses based on small numbers are generally less reliable than those based on larger numbers of people.
- This is a Swedish cohort. Lifestyle and environmental differences may mean the study is not completely representative of the UK population.
One expert from the University of Cambridge also considers another possibility that increased drink consumption could be due to increased thirst before diabetes is diagnosed – that is, the study can't rule out that this finding could be a symptom rather than a cause of diabetes.
The researchers did try and take account of consumption of water and other drinks as a general marker of thirst, but this is still a possibility the study design can't rule out.
Nevertheless, the findings support current understanding of the risk factors for diabetes, which apply to several other chronic diseases.