Drinking diet soda may increase the risk for proliferative diabetic retinopathy — a severe type of diabetic eye disease that can lead to blindness — according to a study published online in the September/October issue of Clinical and Experimental Ophthalmology.

The study is the first to evaluate the link between soft drink consumption and microvascular complications of diabetes.

"In our clinical sample of people with diabetes, consuming more than four cans, or 1.5 liters, of diet soft drinks per week was associated with a twofold increased risk of having proliferative diabetic retinopathy," first author Eva Fenwick, PhD, told Medscape Medical News. Fenwick is a clinical research fellow at the Singapore Eye Research Institute and an assistant professor at the Duke-NUS Medical School, Singapore.

Interestingly, the study did not find a correlation between consumption of regular, sugar-sweetened soft drinks and increased risk for diabetic retinopathy.

Because the study was cross-sectional, further longitudinal studies are needed to determine whether soft drinks are unhealthy alternatives to sugar-sweetened beverages, she added.

Diet soft drinks have been marketed as a healthier option to regular soft drinks, yet a growing body of evidence has suggested that artificial sweeteners may also have detrimental health effects. Past research has linked diet soda to increased cardiometabolic risk, poor cardiovascular outcomes, and type 2 diabetes mellitus.

Although the biological mechanism remains unknown, some researchers hypothesize that diet beverages may "fake out" the body to assume more energy has been consumed than it really has. That may lead to increased hunger and higher calorie intake in the long run.

The study included 609 adults with type 1 diabetes (n = 73; 12.5%), type 2 diabetes (n = 510; 87.5%), or unknown diabetes type (n = 26; 4.3%) at a tertiary eye hospital between 2009 and 2010. The mean age of the participants was 64.6 years. They came from the Diabetes Management Project, a cross-sectional study of English-speaking adults with diabetes in Melbourne, Australia.

Participants underwent objective measurement of diabetic retinopathy and diabetic macular edema with standardized techniques to determine how soft drinks may affect microvascular complications of diabetes.

Participants self-reported soft drink consumption on a 145-question food frequency questionnaire. Of the total sample, 46.8% (n = 285) drank regular soft drinks, and 31.2% (n = 190) drank diet soft drinks.

Almost one quarter (24%) (n = 146) had proliferative diabetic retinopathy.

Compared with no consumption, high levels of diet soft drink consumption (more than four 375-mL cans/bottles per week) were independently linked to an approximately 2.5 times increased odds of having proliferative diabetic retinopathy (odds ratio, 2.51; 95% confidence interval, 1.05 – 5.98). The researchers adjusted results for traditional diabetic retinopathy risk factors, such as diabetes duration, smoking, and body mass index.

Regular soft drink consumption was not linked to diabetic macular edema and the presence or severity of diabetic retinopathy.

The authors note that this last result is consistent with past research. Some studies have found a link between consumption of diet soft drinks, but not regular soft drinks, and vascular complications of diabetes. Others have failed to confirm these findings. The authors mention several explanations for this discrepancy.

"Our finding that regular soft drink was not associated with increased risk of proliferative diabetic retinopathy could be due to the small numbers of high consumers. We had to merge the high-consumer category with the moderate-consumer category, and this may have masked the true relationship," Fenwick told Medscape Medical News.

Because the study was cross-sectional, the researchers could not determine whether people who reported current diet soda consumption had previously drunk regular soda and whether they changed their lifestyle after being diagnosed with diabetic retinopathy. Although the analysis adjusted for changes in dietary habits during the past 5 years, such behavior could have led to an overestimation of the association between diet soda and diabetic retinopathy.

"Although the results of our study must be interpreted within the context of several limitations, they add to the growing body of literature on the harmful effects of diet drinks on a range of health outcomes, including CVD [cardiovascular disease], diabetes, and metabolic syndrome," Fenwick said.

"Given that diet soft drinks are perceived as a healthy alternative to regular soft drinks, clinicians and patients should be aware that diet soft drinks may not be without risks of their own," she concluded.

The authors have disclosed no relevant financial relationships.

Clin Exp Ophthalmol. 2018;46:767-776. Full text

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