Drinking soft drinks every day—including sugar-free diet sodas—is associated with a greater risk of premature death, according to a study of over 450,000 people published Tuesday in JAMA Internal Medicine.
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For the study, researchers looked at data from the European Prospective Investigation into Cancer and Nutrition, which recruited participants from across Europe between 1992 and 2000.
The researchers defined soft drinks as carbonated soda such as colas, diet or low-calorie carbonated drinks, isotonic or energy drinks, and diluted syrups. The researchers did not include fruit juice in their definition of soft drink. They measured consumption by glass, which was defined as 250 milliliter or about 8.5 fluid ounces.
Researchers looked at information about the study sample's diet, including soft drink consumption, as well as their lifestyle, including education level, smoking habits, alcohol consumption, and physical activity.
The researchers excluded participants who already had conditions such as cancer, heart disease, and diabetes at the start of the study, which left them with 451,743 participants, who stayed in the study for an average of 16.4 years. The final study population was 71.1% women and 28.9% men.
The researchers found that, after accounting for factors that could increase risk of death like body mass index (BMI) or smoking, participants who consumed two or more glasses of soft drinks each day were 17% more likely to die early than those who drank less than a single serving of soft drinks per month.
The researchers also looked at how consumption of sugar-sweetened beverages and beverages with artificial sweetener each related to the risk of early death. The researchers found that participants who consumed two or more glasses of sugar-sweetened soft drinks each day were 8% more likely to die early than those who drank less than one glass of a soft drink a month. Those who drank at least two glasses of artificially sweetened soft drinks a day were 26% more likely to die early than those who drank less than one glass of a soft drink a month.
The researchers found no association between soft drink consumption and deaths from cancer of Alzheimer's disease.
Neil Murphy, a scientist at the International Agency for Research on Cancer, and co-author on the study, said the results "provide further support to limit consumption [of soft drinks] and to replace them with other healthier beverages, preferably water."
However, Murphy cautioned that the soft drinks themselves may not be the cause of premature death because "in these types of studies (observational epidemiology) there are other factors which may be behind the association we observed. For instance, high soft drink consumption may be a marker of overall unhealthy diet."
Similarly, Murphy noted they study showed people who drank more soft drinks had higher BMIs and were more likely to smoke tobacco. "We made statistical adjustments in our analyses for BMI, smoking habits and other mortality risk factors which may have biased our results and the positive associations remained," he said. "However, we cannot rule out the possibility that these factors were influencing our findings, hence we cannot say the associations we observe are causal."
Meanwhile, some experts warn that observational studies like this fail to answer the question of whether drinking diet sodas cause harm or is simply associated with unhealthy behavior. According to the New York Times, many nutritionists, epidemiologists, and behavioral scientists think that it may be the case that people who drink diet soda have an unhealthy lifestyle, diet soda consumption notwithstanding.
Vasanti Malik, a researcher at the Harvard T.H. Chan School of Public Health, who was not involved in the new study but led a separate study that challenged a possible link between artificial sweeteners and mortality in women, said, "'It could be that diet soda drinkers eat a lot of bacon or perhaps it's because there are people who rationalize their unhealthy lifestyle by saying, 'Now that I've had a diet soda, I can have those French fries.'" He added, "This is a huge study, with a half million people in 10 countries, but I don't think it adds to what we already know."
In a statement, William Demody, a spokesperson for the American Beverage Association, said, "Soft drinks are safe to consume as part of a balanced diet and the authors of this study acknowledge their research does not indicate otherwise. America's beverage companies are committed to innovation and working to reduce the sugar people get from beverages by introducing more options than ever before with less sugar and zero sugar. Today, more than half of all beverages purchased contain no sugar. No one should overconsume sugar, and we stand by the safety and quality of our products" (Carroll, Reuters, 9/3; Albrecht, MarketWatch, 9/4; Paddock, Medical News Today, 9/4; Mullee et al., JAMA, 9/3).