At a conference last week, University of Miami researchers presented evidence that seemed to link diet soda with an increased risk of stroke and vascular death. However, according to several experts, the study is flawed. They say diet soda drinkers should disregard the warning.
Jennifer Cleary from the Lipid Disorders and Metabolic Syndrome Clinic at Northwestern Memorial Hospital in Chicago told Clinical Advisor, "There are a lot of factors that were not taken into consideration, so we can't really assume that there is a causal relationship between diet soda and stroke." In other words, the researchers found a correlation, not causation. "[People drinking diet soda] might also be consuming fast food and making other unhealthy lifestyle choices."
For example, diet soda drinkers are more likely to be overweight and to have diabetes, said Richard Besser, MD, chief health and medical editor at ABC News. "[The researchers] didn't look at how much salt [participants] took in, they didn't look at what other foods they ate. Those things we know are associated with stroke and heart attack," Besser said. "The study population may have been at a higher-than-normal risk for cardiovascular events, with an event rate of 22 percent compared with the expected rate of 8 to 10 percent."
Cleary also criticized the failure of the researchers to survey the study participants' soda consumption throughout the duration of the study. Their soda intake was assumed to stay constant over the course of nine years.
Furthermore, she and other experts said the sample size used in the study was too small. Even though 2,500 people were surveyed, only 4.5 percent reported drinking (diet or regular) soda daily; that's too few to produce a statistically meaningful result rather than just a random fluctuation.
"I think we have to interpret the findings about diet soda very carefully," Walter Willett, MD, chair of the department of nutrition at Harvard School of Public Health, told the Clinical Advisor. "[After] almost any first report, we shouldn't really change our behavior, because it could easily have occurred by chance."
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