Drinking Even Diet Soda May Be Harmful to Your Health

< Jul. 25, 2007 > -- Drinking more than one soft drink daily - even if it is the sugar-free kind - may be associated with an increased incidence of metabolic syndrome, which is a cluster of risk factors linked to the development of diabetes and cardiovascular disease, a study finds.

The link to diet soda found in the study was "striking" but not entirely a surprise, reports Dr. Ramachandran Vasan, study senior author and professor of medicine at Boston University School of Medicine.

There had been some hints of it in earlier studies, he says. The findings were published this week in Circulation: Journal of the American Heart Association.

"But this is the first study to show the association in a prospective fashion and in a large population," Dr. Vasan states.

Framingham Study Follow-Up

The Framingham Heart Study  has been following 6,000 participants since 1948. The heart study participants were free of any signs of metabolic syndrome when the study began.

Metabolic syndrome includes the following signs:

• high blood pressure

• elevated levels of triglycerides

• low levels of heart-protecting HDL cholesterol

• high fasting blood sugar

• excessive waist circumference

Metabolic syndrome is the presence of three or more of these risk factors. "But this is the first study to show the association in a prospective fashion and in a large population," Dr. Vasan asserts.

Over the four years of the study, people who consumed more than one soft drink of any kind each day were 44 percent more likely to develop metabolic syndrome than those who did not drink a soda a day.

Explanations Unproven

The link between diet soft drink consumption and metabolic syndrome was clear even when the researchers accounted for other factors, such as levels of saturated fat and fiber in the diet, total calorie intake, smoking, and physical activity. A variety of unproven explanations have been proposed for this association. One theory is that the high sweetness of all soft drinks makes a person more prone to eat sugary, fattening foods. Another is that the caramel content of soft drinks promotes metabolic changes that lead to insulin resistance.

"These are hotly debated by nutritional experts," Dr. Vasan says. Dr. Vasan, who notes that he is not a nutritional expert, says he leans toward the theory that "this is a marker of dietary behavior" - that people who like to drink sweet soda also like to eat the kind of foods that cardiac nutritionists warn against. "But we cannot infer causality," Dr. Vasan cautions, meaning there is no proof that soda itself is the villain. "We have an association. Maybe it is a causal one or maybe it is a marker of something else." Carefully controlled animal studies might resolve the cause-and-effect issue, he states.

Study Clarified After Its Release

Shortly after the study's release, the American Heart Association (AHA) clarified the findings, stating this report "does not show that soft drinks cause risk factors for heart disease." The statement also acknowledged that other factors could explain the development of risk factors for heart disease and that more research is needed.

Response from Soft Drink Industry

The American Beverage Association states that it appreciates the heart group made clear "the report does . . . not show that soft drinks cause an increased risk of heart disease and it recognizes that diet soft drinks are a good option for those looking to cut calories in their beverages."

Susan Neely, president of the American Beverage Association, adds, "The study does not establish any link between soft drinks, regular or diet, and increased risk of heart disease . . . diet soft drinks are terrific if you're trying to watch weight and want something refreshing that tastes good and has no calories."

No Final Verdict

Dr. Elizabeth G. Nabel, director of the US National Heart, Lung, and Blood Institute (NHLBI), which funds the Framingham Heart Study, says, "Other studies have shown that the extra calories and sugar in soft drinks contribute to weight gain, and therefore heart disease risk. This study echoes those findings by extending the link to all soft drinks and the metabolic syndrome."

Dr. Suzanne R. Steinbaum, director of Women and Heart Disease at Lenox Hill Hospital in New York City, says, "There is no safe way of eating junk food, just as we learned the lesson from trans fats and partially hydrogenated oils often found in fat-free or low-fat cookies. Diet soda does not protect us from the development of what we are trying to avoid by consuming it."

Always consult your physician for more information.

What is Metabolic Syndrome?

Metabolic syndrome is a condition that includes the presence of a cluster of risk factors specific for cardiovascular disease. Metabolic syndrome significantly raises the risk of developing diabetes, heart disease, and/or stroke.

The American Heart Association (AHA)  recognizes metabolic syndrome as a problem of growing concern, especially for those over age 60. Because the population of the US is aging and because metabolic syndrome prevalence increases with age, the AHA has estimated that metabolic syndrome soon will become the primary risk factor for cardiovascular disease, ahead of cigarette smoking. Increasing rates of obesity are also thought to be related to the increasing rates of metabolic syndrome.

The cluster of metabolic factors involved as defined by the National Cholesterol Education Program's Adult Treatment Panel III (NCEP-ATP III) report, sponsored by the National Heart, Lung, and Blood Institute, includes:

• abdominal obesity, in which the waist circumference measures more than 35 inches for women and more than 40 inches for men - an increased waist circumference is the form of obesity most strongly associated with metabolic syndrome.

• high blood pressure of 130/85 mm Hg (millimeters of mercury) or higher - normal blood pressure is defined as 120 mm Hg or lower for systolic pressure (the top number), and 80 mm Hg or lower for diastolic pressure (the bottom number). High blood pressure is strongly associated with obesity and is often found in persons with insulin resistance.

• insulin resistance - a condition in which being overweight or obese makes it hard for cells to respond to insulin. The body releases more insulin to help glucose enter the cells until blood sugar increases. Insulin resistance can lead to diabetes.

• high triglyceride levels of more than 150 mg/dl (milligrams per deciliter) - triglycerides are a type of fat in the blood

• low HDL cholesterol(the "good" cholesterol) less than 40 mg/dl for men and less than 50 mg/dl for women

• proinflammatory state - a condition that involves elevated C-reactive protein, a substance that is thought to be a marker for inflammation in the body

• prothrombotic state - a condition that involves elevated blood clotting factors

While there are few symptoms experienced in metabolic syndrome, there may be several signs. A symptom is evidence of disease or physical disturbance that a person experiences and can describe. By contrast, a sign is objective evidence of disease as observed and interpreted by a physician or other clinician.

Factors such as high blood pressure, elevated triglycerides, and/or overweight or obesity may be signs of metabolic syndrome. Persons with insulin resistance may have acanthosis nigricans, which is darkened skin areas on the back of the neck, in the armpits, and under the breasts. In general, however, persons do not directly experience symptoms of metabolic syndrome.

The indications of metabolic syndrome may resemble other conditions.

Always consult your physician for more information.