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Diet Soda and Diabetes: Why It's So Hard On the Eyes

Drinking more than 4 diet sodas weekly may more than double your risk of getting diabetic retinopathy, new research suggests.

man in sunglasses sitting at counter with soda Diet—not regular—soda consumption linked to greater incidence of diabetic retinopathy, a condition that can lead to blindness if not treated. (Photo: Unsplash, Brooke Cagle)

Drinking diet sodas may help you feel more in control of calorie intake and weight control, but a heavy diet soda habit may harm your eye health, new research suggests.1

Those in the study who drank more than 4 cans, or more than 1.5 liters, of diet soft drinks in a week had more than a two-fold risk of getting an advanced form of diabetic retinopathy (DR), a complication of diabetes that can lead to the need for treatments and to vision loss.2

Regular soft drink intake was not linked with the eye condition, the researchers say.

The study is published in Clinical & Experimental Ophthalmology.

So is drinking just a little diet soda OK? "Based on our data, no consumption of diet soda would be the safest level," says Eva Fenwick, PhD, a clinical research fellow at the Singapore Eye Research Institute, who led the study.

Study Details

Fenwick's team from the Singapore Eye Research Institute and other institutions, evaluated 609 men and women with diabetes, on average about age 65. They were participants in the Diabetes Management Project, a study of adults with diabetes in Melbourne, Australia.

Most, 510, had type 2 diabetes; 73 had type 1 and the remaining 26 had diabetes with type not specified. All had undergone eye exams between 2009-2010.  The participants answered questions about their soda habits, both diet and regular.

The researchers found that about 47% drank regular soft drinks while 31% drank diet drinks.

 

They classified soda drinkers as none if they had less than a can a week, moderate at 1-4 cans weekly and high if they drank over 4 cans weekly.

One study limitation is the lack of reporting; 127 didn't provide information on diet soda drinking; 129 didn't report information regular soft drinks.

The exams revealed that nearly one-fourth of the participants had proliferative diabetic retinopathy. That is the more advanced form of the complication. In the earlier form, nonproliferative DR, damage occurs to the small retinal blood vessels. In proliferative DR, the damage is more severe and new, abnormal blood vessels may grow and bleed into the eye.2

Treatments can prevent vision loss, but if left untreated, DR can lead to vision loss and blindness.

The researchers found that link, or association, between diet sodas and proliferative DR, even after taking into account other risk factors for the eye complication, such as the duration of the diabetes diagnosis and smoking.

They found no link between diet soda intake and the earlier form of DR, nor did they find a link between drinking regular sodas and DR.

Their bottom line: Drinking more than 4 cans, or 1.5 liters, a week of diet soft drinks raise the risk of having proliferative DR by more than two fold. The researchers say more studies are needed to figure out why the association exists. More studies are also needed, to verify the findings.

One study limitation, Dr. Fenwick says, is that the researchers measured soda intake during the past 12 months, so it was not possible to determine how long they had the soda habit reported. However, other research has pointed out ill effects from diet soft drinks, changing  the reputation of the beverage, she says. 

Although artificially sweetened sodas have been marketed as a healthier alterative to regular sodas due to their lack of sugar, ''there is a growing body of evidence, including well-designed prospective data, linking diet soft drinks with poor cardiovascular outcomes, metabolic syndrome, and type 2 diabetes. Our study adds to this literature." She advises those with diabetes who drink diet drinks to speak to their doctor about whether they should rethink the habit.

Second Opinions

The results are interesting, says Sunir Garg, MD, FACS, retina surgeon and professor of ophthalmology, Wills Eye Hospital, Philadelphia. He reviewed the findings but was not involved in the study.

"I think most of us would have guessed that the regular soda group would have had worse [eye] disease and that the diet drinks would have had less," he tells OnTrackDiabetes. The finding, of course, was the opposite.

"It's not clear why that is the case," he says. While the mechanisms are not clear, he says it is also possible that the findings were due to chance. It was not a big study, he points out, so additional research is needed to see if the link would hold up.

"There has been some other work that suggests that diet soda causes heart disease and problems with the blood vessels, so that might be a relationship," he says.

Another expert, Elena A. Christofides, MD, FACE, an endocrinologist and CEO Of Endocrinology Associates in Columbus, Ohio, also reviewed the findings. She says that ''artificial sweeteners cause an increase in leptin response without a commensurate change in insulin."  Leptin is a hormone that helps suppress appetite.  And she adds: "Leptin is known to increase vascular proliferation and smooth muscle cell migration, which are the two key players in the development of retinopathy.'' Smooth muscle cell migration can occur in response to blood vessel injury.

Industry Reach Out

OnTrackDiabetes reached out to the American Beverage Association, an industry group representing soft drink makers and others, for comment on the findings.
As yet, the association has not provided a reply.

Bottom Lines

Dr. Fenwick's team notes that more study is needed as the research on this topic is sparse.
Dr. Garg says that for now, it suggests that ''all of us need to eat real food, the type of food that our great grandparents might have had-real food that comes from plants and animals that goes bad if you keep it on the counter too long."

Much other research has found that drinking soft drinks can increase the risk of cardiovascular disease.

According to Dr. Christofides: "I advise my patients to avoid all artificial sweeteners of all types at all times."

Dr. Fenwick says she cannot say for sure if the results would apply to those in the US, since the patients were all getting their healthcare in Melbourne, Australia, and the two healthcare systems are very different. However, she says that more than half of the participants were not Australian natives but were born overseas.

Neither Drs. Fenwick, Garg or Christofides have relevant disclosures.

Updated on: February 28, 2019
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