More bad news for soda lovers: in addition to obesity and heart disease, the sugary drinks may be tied to asthma and chronic obstructive pulmonary disease (COPD), Australian researchers found.
People who consumed at least a half a liter of soft drinks a day were more than twice as likely to develop either lung condition compared with those who didn't partake at all (OR 2.33, 95% CI 1.51 to 3.60), Zumin Shi, MD, of the University of Adelaide in Australia, and colleagues reported in Respirology.
The cross-sectional study, however, couldn't prove causality, and researchers not involved in the study suspect an overall unhealthy diet effect might be at play.
"High soda intake is a good marker for poor overall diet, and poor overall attention to health," David Katz, MD, director of the Prevention Research Center at Yale University in New Haven, Conn., said in an email to MedPage Today. "It likely suggests greater exposure to everything from tobacco smoke to air pollution."
Sugar-sweetened beverages have long been linked to a host of poor health outcomes, including stroke and heart disease, but no study has yet assessed potential ties to asthma or COPD, the researchers said.
There are many potential explanations for the increased burden of asthma in Western countries -- less exposure to indoor allergens, improved hygiene, and use of antibiotics (the "hygiene hypothesis"), as well as poor diet and increased obesity -- but fewer noted risk factors for COPD.
Smoking, of course, is a major one, but up to 50% of airway obstruction can't be explained away by cigarette use, they wrote, thus the need to identify novel risk factors.
The group looked at data from the South Australian Monitoring and Surveillance System on 16,907 adults, mean age 46.7, who responded to phone interviews from March 2008 to June 2010.
The prevalence of asthma and COPD, based on self-reported doctor diagnosis, was 12.5% and 4.4%, respectively.
Though the vast majority (72%) said they didn't drink any soda at all, 11.4% reported taking down more than a half a liter of soft drinks every day. In addition to carbonated brand-name soft drinks, lemonade, flavored mineral water, and sports drinks were consumed.
Shi and colleagues found that folks who drank this level of soda had a higher prevalence of asthma and COPD than those who didn't drink any (14.7% versus 11.9% and 6% versus 4.2%, respectively).
In multivariate analyses adjusting for sociodemographic factors, intake of fruit and vegetables, and other life style factors, drinking half a liter of soda a day was associated with an odds ratio of 1.26 for asthma (95% CI 1.01 to 1.58) and an OR of 1.79 for COPD (95% CI 1.32 to 2.43) compared with never drinking soda.
The researchers also saw combined effects for drinking soda and smoking. Consuming more than half a liter a day and being a current smoker carried a 6.6-fold greater risk of COPD and a 1.5-fold higher risk of asthma than not smoking and drinking soda, they reported.
"The combined effect of soft drink consumption and smoking on asthma/COPD emphasizes the importance of lifestyle factor clustering in the etiology of asthma/COPD," they wrote. "Promoting a healthy lifestyle should be encouraged as one means of preventing asthma/COPD."
The mechanisms behind the relationships, however, are unclear. Both asthma and COPD are associated with inflammation, and it could be that foods promoting oxidative stress and inflammation could affect the pathogenesis of these diseases, they wrote.
Drinking soda has also been tied to a higher risk of obesity, which in turn leads to a greater likelihood of developing both lung diseases, they said.
And studies have shown that chemicals such as phthalates from plastic bottles, as well as allergies to preservatives such as nitrites and sulphites, may be linked to asthma.
In addition to not being able to prove causality, the study was limited by its reliance on self-reported data.
Still, Shi and colleagues concluded that "regardless of whether there is a cause-and-effect relationship, the public health implications of consumption of large volumes of soft drink are substantial."
The researchers reported no conflicts of interest.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner