Middle-aged adults who drink more than one drink per day of a diet or regular soft drink have a more than 40-percent greater rate of having or developing metabolic syndrome, according to an analysis of Framingham Heart Study data published online July 23 by Circulation.

A person is considered to have metabolic syndrome if he or she has three or more of the following five risk factors: waist circumference greater than or equal to 35 inches (women) or 40 inches (men), fasting blood glucose of greater than or equal to 100 mg/dL, triglycerides greater than or equal to 150 mg/dL; blood pressure greater than or equal to 135/85 mmHg, and high-density lipoprotein cholesterol below 40mg/dL for men or below 50 mg/dL for women.

“Other studies have shown that the extra calories and sugar in soft drinks contribute to weight gain, and therefore heart disease risk,” said Elizabeth G. Nabel, MD, Director, NHLBI. “This study echoes those findings by extending the link to all soft drinks and the metabolic syndrome.”

While the authors acknowledge that the increased risk of metabolic syndrome associated with high-calorie, high-sugar regular soft drinks might be expected, the similar risk found among those drinking diet sodas is more challenging to understand. It is worth noting that dietary patterns are similar across drinkers of both regular and diet soft drinks.

“Although our study adjusted for lifestyle factors, it is known that people who regularly drink soft drinks - even diet sodas - are also known to eat foods that are higher in calories and fat, and get less physical activity,” said Ramachandran Vasan, MD, professor of medicine at Boston School of Medicine, senior author of the paper.

“High soft drink consumption may in fact be a marker for metabolic syndrome risk, but more study is needed,” said Ravi Dhingra, MD, instructor in medicine, Harvard Medical School, and lead author.

Data was collected in two ways, via physician-administered questionnaire that captured average daily of consumption of 12 ounce soft drinks, and a self-administered food frequency questionnaire that captured the frequency of diet versus regular soft drink intake. Both questionnaires were recorded during Heart Study visits scheduled in 1987-1991 and 1995-1998, and accounted for nearly 9,000 person observations.

“Our results point to the importance of long-term observational studies such as the Framingham Heart Study, which allow us to take a closer look at how aspects of diet are inter-related with health risks,” said Caroline Fox, MD, medical officer, Framingham Heart Study and study co-author.