By Kathleen Doheny
WEDNESDAY, Feb. 9 (HealthDay News) -- Diet soda fans who drink the beverages every day may be cutting down on calories, but they also might be boosting their risk of stroke, new research suggests.
"In our study, we saw a significant increased risk among those who drank diet soda daily and not regular soda," said Hannah Gardener, an epidemiologist at the University of Miami Miller School of Medicine, who was slated to present her research Wednesday at the International Stroke Conference 2011 in Los Angeles.
Why the link? "It's unknown at this point," she said.
Stroke is the third leading cause of death, behind heart disease and cancer, in the United States. More than 137,000 people a year die from stroke, according to the American Stroke Association.
Previous research by others has found that those who drank more than one soft drink a day, whether regular or diet, were more likely than non-drinkers to have metabolic syndrome, a cluster of risk factors including high blood pressure, elevated triglycerides (blood fats), low levels of good cholesterol, high fasting blood sugar and large waists. Metabolic syndrome, in turn, raises the risk of diabetes and cardiovascular disease, experts agree.
Gardener and her colleagues evaluated the soda habits of 2,564 people enrolled in the large Northern Manhattan Study (NOMAS) to see if there was an association, if any, with stroke. The participants were 69 years of age, on average, and completed food questionnaires about the type of soda they drank and how often.
During the average nine-year follow-up, 559 vascular events occurred, including strokes caused by hemorrhage and those caused by clots, known as ischemic strokes.
The researchers controlled for such factors as age, gender, ethnicity, physical activity, calorie intake, smoking and alcohol drinking habits and still found that those who drank diet soda daily -- compared to those who drank no soda -- were 61 percent more likely to have a vascular event.
The researchers then controlled for the presence of metabolic syndrome, vascular disease in the limbs and heart disease history; the link still held, albeit at 48 percent.
While the study found a possible association between diet soda and stroke risk, it did not demonstrate a cause and effect.
"If our study is replicated," Gardener said, "it would suggest diet soda is not optimal."
Dr. Patrick Lyden, chief of neurology at Cedars-Sinai Medical Center in Los Angeles, reviewed the findings but was not involved in the research. "My first thought was, 'The correlation has to be accidental,'" he said.
But he said the science in the study looks sound. "There still could be some sort of accidental correlation," he said. What to do? "Wait for repeated studies to show a risk and in the meantime, all things in moderation."
He tells his patients to avoid soda, whether diet or regular, on a daily basis. "An occasional soda never hurt anybody," he said. "Once or twice a week to me seems to be rational."
In a separate study, Gardener also found high salt intake was linked to a higher risk of stroke. Using the same data, she looked at 2,657 participants of NOMAS, evaluating their salt intake and following them for nearly 10 years.
During that time, 187 ischemic strokes occurred. Those who consumed more than 4,000 milligrams a day of sodium had more than double the risk of ischemic stroke than those who consumed less than 1,500 milligrams a day.
How much salt is ideal? The American Heart Association recommends less than 1,500 milligrams a day. The current U.S. Dietary Guidelines for Americans recommends eating less than 2,300 milligrams a day and even less -- 1,500 milligrams a day -- for those who are 51 and older and certain other people. Among those who should stop at 1,500 milligrams of salt a day are blacks and people with hypertension, diabetes or chronic kidney disease.
To learn more about strokes, visit the American Heart Association.
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