Drinking as little as one can of soda per day - either regular or diet - is associated with a 48 per cent increased risk of "metabolic syndrome", a key predecessor of heart disease and diabetes, according to new results released on Monday.
Researchers previously had known that drinking regular sodas contributed to the risk of metabolic syndrome, but this is the first finding implicating diet sodas, according to results published online in Circulation: Journal of the American Heart Association.
The researchers were uncertain why diet soda had such a large effect.
Dr Ramachandran S. Vasan of Boston University School of Medicine, the lead author of the study, said it is unlikely that an ingredient in soda causes the effect. More likely is that consuming sweet sodas changes dietary patterns or that soda is simply a marker for the poor eating habits of the participants.
Not unexpected
Dr Meir Stampfer of Harvard Medical School, who was not involved in the study, said the findings were not unexpected, although he added, "I'm surprised by the magnitude of the association."
Stampfer previously had reported that diet sodas increase the risk of obesity and high blood pressure.
Soda makers, however, rejected the study outright.
Susan K. Neely, president and chief executive of the American Beverage Association, said that "the assertions defy the existing body of scientific evidence, as well as common sense ... It is scientifically implausible to suggest that diet soft drinks - a beverage that is 99 per cent water - cause weight gain or elevated blood pressure."
Cluster of symptoms
Metabolic syndrome is a cluster of symptoms that includes excessive abdominal fat, high blood-glucose levels, high blood pressure, high blood triglycerides and low levels of high-density lipoprotein, the "good" cholesterol.
People with three or more of these symptoms have double the normal risk of heart disease and diabetes.
In the study, sponsored by the National Heart, Lung and Blood Institute, Vasan and his colleagues studied more than 2,400 middle-aged, white residents of Framingham, Massachusetts. At the beginning of the study, those who had consumed more than one soda per day - either regular or diet - had a 48 per cent higher risk of having metabolic syndrome.
The team then focused on the more than 1,600 people who did not have metabolic syndrome at the start of the study and followed them for at least four years. Those who drank at least one soda per day had a 44 per cent higher risk of developing metabolic syndrome during the four years of the study.
Those who drank at least one soda per day also had:
- a 31 per cent greater risk of becoming obese;
- a 30 per cent higher risk of having a larger waist line;
- a 25 per cent higher risk of developing high blood triglycerides or high blood sugar;
- a 32 per cent greater risk of having low levels of good cholesterol;
- a trend toward an increase risk of high blood pressure.
Higher in calories
The percentages were the same whether a subject drank regular or diet soda.
Vasan said research has shown that people who drink sodas also tend to have a diet that is higher in calories, higher in saturated fats and trans-fats and lower in fibre. They also are more sedentary.
The authors tried to control for all those factors in the diet, but "even after all that, we still found an increased risk", he said.
"Maybe it is very difficult to adjust for lifestyle."
