“Ditch the Diet Coke! People who drink two glasses a day at ‘higher risk of early death’,” warns the Daily Mirror. The headline is based on a new study that looked at whether soft drink consumption was linked to poorer long-term health outcomes.
Researchers asked more than 450,000 adults (average age 51) from 10 European countries about their consumption of soft drinks. Soft drinks included sugary and artificially sweetened fizzy drinks such as cola as well as diluted cordial.
The researchers followed up the participants for an average of 16 years and found that people who drank 2 or more glasses of any type of soft drink a day were 17% more likely to have died during the study, compared to people who drank less than 1 soft drink a month.
Sugary drinks were linked to deaths from digestive diseases (such as liver disease), while artificially sweetened drinks were linked to deaths from cardiovascular diseases such as heart disease.
While the link between sugar consumption and health problems is well established, it is unclear why artificially sweetened drinks could have an adverse effect on health.
Due to the nature of the study the researchers were unable to prove that soft drinks are directly to blame for the small increased risk of death. However, the researchers say their findings add support to public health campaigns urging people to drink water instead of soft drinks. After all, tap water in the UK is safe to drink and free of calories.
Where did the story come from?
The study was carried out by a big group of researchers from a range of institutions across Europe, led by the International Agency for Research on Cancer in France. It was funded by the European Commission and the International Agency for Research on Cancer. It was published in the peer-reviewed journal JAMA Internal Medicine and is free to read online.
The study was widely reported in the UK media. While some – like The Sun and the Daily Mirror – overstated the strength of the evidence, reports in The Guardian and The Times explained the study’s limitations.
What kind of research was this?
This was a cross-sectional cohort study, which used data from the European Prospective Investigation into Cancer and Nutrition (EPIC).
While large cohort studies are useful for investigating links between risk factors (such as soft drink consumption) and outcomes such as death, they cannot prove that the risk factors directly cause the outcomes. Other factors could be involved.
With cross-sectional studies, we only know about drink consumption at 1 point in time. That means we cannot tell how soft drink consumption changed over time.
What did the research involve?
Researchers recruited 521,330 people from 10 European countries: the UK, Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain and Sweden. The participants were asked to fill in questionnaires about what they ate and drank (including soft drinks), and also about their health and lifestyle.
For this study, researchers did not include anyone who had cancer, heart disease, stroke or diabetes at the start of the study, or who reported unlikely dietary results (such as eating an unusually high or low amount of calories), or who had no information about soft drink consumption or follow-up data. This left a total of 451,743 participants, 71% of them women.
People were followed up either directly through phone interviews or postal questionnaires, or through registries in the country they lived in, or both. Follow-up ranged from 11 years in Greece to 19 in France, with an average of 16.4 years.
Researchers adjusted their figures to take account of a wide range of possible confounding factors:
- alcohol consumption
- smoking status
- body mass index (BMI)
- physical activity
- menopausal status and use of HRT
- how much red and processed meat, coffee, fruit and vegetables and fruit and vegetable juice people consumed
They then calculated the relative chances of having died during the study for people who drank more or less total soft drinks, sugary soft drinks and diet soft drinks. They also looked at causes of death, to see whether certain causes were more strongly linked to types of soft drinks.
What were the basic results?
During the study, 41,693 of the 451,743 participants died (9.2%).
Compared to people who drank less than 1 soft drink of any type per month, people who had 2 or more glasses a day were 17% more likely to have died (hazard ratio (HR) 1.17, 95% confidence interval (CI) 1.11 to 1.22).
The increased risk was true for both sugary and artificially sweetened soft drinks. Compared with people who drank less than 1 glass a month:
- people who drank 2 or more sugary soft drinks were 8% more likely to have died (HR 1.08, 95% CI 1.01 to 1.16)
- people who drank 2 or more artificially sweetened soft drinks were 26% more likely to have died (HR 1.26, 95% CI 1.16 to 1.35)
When researchers compared chances of death from different diseases, they found:
- people who drank more than 2 artificially sweetened soft drinks per day compared to less than 1 glass per month, were 52% more likely to have died of cardiovascular disease (HR 1.52, 95% CI 1.30 to 1.78)
- people who drank 1 or more sugary soft drinks per day compared to less than 1 per month were 59% more likely to have died of digestive diseases (HR 1.59, 95% CI 1.24 to 2.05)
How did the researchers interpret the results?
The researchers said that “consumption of total, sugar-sweetened and artificially sweetened soft drinks was positively associated with all-cause deaths in this large European cohort; the results are supportive of public health campaigns aimed at limiting the consumption of soft drinks”.
This is not the first study to find a link between sugary soft drinks and poorer health. Doctors think that sugary soft drinks contribute to people becoming overweight, and also increase the chances of type 2 diabetes by causing sugar “spikes” in the blood when consumed.
The situation is less clear when it comes to artificially sweetened soft drinks. Studies have had conflicting results. Although artificial sweeteners have no or low calories, some studies have suggested they may also cause spikes in blood sugar.
However, the study has limitations that mean we should treat the results with caution. It is a cross-sectional study, which means we only know what people were eating and drinking at 1 point in time. Although the researchers tried to account for a range of potential confounding factors, there may be other factors affecting the results. For that reason we cannot say that soft drinks caused higher death rates.
One possibility is that people who drank more artificially sweetened soft drinks did so because they were worried about their weight or had other health concerns, so switched from sugary drinks to what they thought were healthier options. That would mean that people choosing artificially sweetened drinks were already less healthy than those who drank sugary soft drinks at the start of the study.
So there’s no need to panic about the headlines suggesting that diet drinks will shorten your life.
Taking all that into account, it remains the case that drinking a lot of soft drinks is not recommended as part of a healthy diet. Water and unsweetened tea or coffee are likely to be healthier options. Replacing soft drinks with tap water is not only likely to be healthier but could save you a lot of money.