Researchers have found a correlation between drinking diet soda and metabolic syndrome — the collection of risk factors for cardiovascular disease and diabetes that include abdominal obesity, high cholesterol and blood glucose levels — and elevated blood pressure.

The scientists gathered dietary information on more than 9,500 men and women ages 45 to 64 and tracked their health for nine years.

Overall, a Western dietary pattern — high intakes of refined grains, fried foods and red meat — was associated with an 18 percent increased risk for metabolic syndrome, while a ‘prudent’ diet dominated by fruits, vegetables, fish and poultry correlated with neither an increased nor a decreased risk.

But the one-third who ate the most fried food increased their risk by 25 percent compared with the one-third who ate the least, and surprisingly, the risk of developing metabolic syndrome was 34 percent higher among those who drank one can of diet soda a day compared with those who drank none.

"This is interesting," said Lyn M Steffen, an associate professor of epidemiology at the University of Minnesota and a co-author of the paper, which was posted online in the journal Circulation. "Why is it happening? Is it some kind of chemical in the diet soda, or something about the behaviour of diet soda drinkers?"

New York Times