Is there a link between diet soda and heart disease?

ARCHIVED CONTENT: As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date each article was posted or last reviewed. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician. 

I’m a big fan of diet soda. I like the taste, and I love that it doesn’t have any calories. I can drink two or three diet sodas a day and not worry about gaining weight. But a new study has me wondering if enjoying the sweetness of soda without the sugar and calories is such a good thing after all.

University of Miami and Columbia University researchers followed roughly 2,500 New Yorkers for 10 years. All of the study volunteers were over age 40 and had never had a stroke. At the start of the study, each participant indicated her or his diet soda intake as “none” (less than 1 per month), “light” (1 diet soda a month to 6 diet sodas a week), or “daily” (1 or more a day). Each year, researchers contacted participants by phone to ask them about changes in risk factors and medications, as well as any health problems and hospitalizations that may have occurred.

At the end of 10 years, the daily diet soda drinkers were more likely to have had a stroke or heart attack, or to have died from vascular disease. The increased risk remained even after study investigators accounted for smoking, exercise, weight, sodium intake, high cholesterol, and other factors that could have contributed to the difference. The results were published online in the Journal of General Internal Medicine.

Both regular and diet soft drinks were linked with certain, but separate, cardiovascular disease risk factors. In this study, frequent diet soda drinkers were more likely to be former smokers and have higher blood sugar, high blood pressure, and, ironically, larger waistlines. They were also more likely to have metabolic syndrome. That’s the name for a cluster of risk factors—high blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol levels—that occur together and increase the risk for heart disease, stroke, and type 2 diabetes. Folks who drank regular soda were more likely to smoke and eat more carbohydrates, but were less likely to have diabetes or high cholesterol.

A study such as this one can only hint at an association between diet soda and cardiovascular risk. It can’t pinpoint a cause and effect. But it’s not the first to implicate diet soda as a cardiovascular risk factor. A report from the Multi-Ethnic Study of Atherosclerosis, published in the journal Diabetes Care, found that people who drank diet soda every day had a 36% greater risk of developing metabolic syndrome and a 67% greater risk of developing diabetes. Both of these conditions greatly raise the odds of having a stroke or heart attack. It’s a little surprising that diet soda drinkers were more like to develop two particular components of metabolic syndrome: larger waistlines and higher fasting glucose levels (results consistent with the New York study results).

So far, research on diet soda’s relationship to cardiovascular disease raises more questions than it answers. For example, do people who drink a lot of diet soda have other behaviors or conditions that independently increase their risk of cardiovascular disease? We also don’t have a good understanding of the biological effects of artificial sweeteners (see this Harvard Health Letter article for more on this topic). Manufacturers use a variety of artificial sweeteners in soft drinks, and surely new ones will come on the market. So it is difficult to tease out the effects of a particular sweetener—or beverage for that matter, because a range of drinks come in sugar-free form, not just soda.

Sometimes making a healthful choice is a slam dunk. Quitting smoking and exercising more are very good for you. There’s no debate about that. Other times it’s a tougher call. Surely, no one needs to consume soft drinks of any kind. But is it a problem to do so?

My husband gently (but persistently) tells me there is nothing good about drinking diet soda, not even the taste I claim to enjoy so much. The evidence seems to back him up. For me, I have realized (time and again) that I just feel better when I don’t drink diet soda. When I make the effort, I’m reminded how much I enjoy other beverages such as carbonated water or iced tea.

Wish me luck as I once again try to get off diet soda.

Do you drink diet soft drinks? Do you notice any negative effects from doing so? If you’ve kicked the habit, let us know why and how you did it.