Just one can of sugary soft drink raises the relative risk of diabetes by more than a fifth, a study has found.

Every extra can consumed a day increased the chances of having the disease by 22%, compared with drinking one can a month or less.

The increase in risk only fell slightly after adjusting the findings to take account of body mass index (BMI).

This suggests it was not simply being overweight that led to the trend, said the researchers and that sugar-sweetened drinks have an effect on the body unrelated to obesity.

The results of the study conducted in the UK and eight other European countries broadly mirror previous findings from mostly American research.

A total of 350,000 individuals were questioned about their diet, including their consumption of sugar-sweetened and artificially sweetened "lite" soft drinks and juices.

All were participants in the European Prospective Investigation into Cancer and Nutrition (Epic) study looking at links between diet and cancer.

Incidence of type 2 diabetes was compared with consumption of 340ml servings of sweetened drinks, equivalent to a normal-sized can of cola.

A statistically significant association was seen between high sugary drink consumption and type 2 diabetes risk.

The disease occurs when the body stops responding properly to the hormone insulin, leading to rising blood sugar levels.

Unlike type 1 diabetes, it is lifestyle-related and not an auto-immune condition.

Writing in the journal Diabetologia, the researchers said their study "corroborates the association between increased incidence of type 2 diabetes and high consumption of sugar-sweetened soft drinks in European adults".

An increased risk of diabetes was also linked to consumption of artificially sweetened soft drinks, but the association faded away when BMI was taken into account.

In this case, it looked as if body weight was responsible for the trend rather than the drink itself.

Fruit juice consumption was not associated with diabetes incidence.

Speaking on RTÉ's Morning Ireland, consultant endocrinologist and obesity expert Professor Donal O'Shea welcomed the study.

He said there were real long-term health risks from the over-consumption of fizzy drinks.

He said: "I think it is a landmark study because we've had up until now the association of sugar-sweetened drinks with diabetes.

"This says it's causal. And this says it's causal in what we would call a dose-dependent fashion, so the more you drink of these sugar-sweetened drinks, the more likely you are to get type 2 diabetes.

Dr O'Shea, who runs an obesity clinic in Dublin, said sugar-sweetened drinks should be seen as a treat and preferably only taken on special occasions, such as Christmas, Easter and parties.

He called on parents to take steps to stop children consuming fizzy drinks, which he described as "nutritionally empty".

Commenting on the results of the study, statistics expert Professor Patrick Wolfe, from University College London, stressed the importance of putting the results in perspective.

He pointed out that the absolute risk of type 1 diabetes was low at around 4% of the adult UK population.

"In and of themselves, sugary soft drinks are only part of the picture - they're just one of the potential risk factors for type 2 diabetes," he said.

"But since they are one we can easily eliminate - by switching to diet soft drinks or, even better, cutting them out of our diets altogether - it makes good sense to do so.

"The bottom line is that sugary soft drinks are not good for you - they have no nutritional value and there is evidence that drinking them every day can increase your relative risk for type 2 diabetes.

"But your overall likelihood of developing type 2 diabetes will depend on your individual risk factors - primary among them your weight and level of physical fitness."