Experts have issued a warning against drinking large quantities of cola, saying it could lead to muscle problems, an irregular heartbeat and bone weakness.

The number of cola lovers suffering health issues is on the rise, they said, adding there had been a food industry push towards an "increase in portion sizes".

As well as tooth decay, diabetes and "softening" of the bones, doctors have seen patients suffering from hypokalaemia where potassium levels in the blood drop too low.

This can increase the risk of muscle problems and heart rhythm abnormalities, which could prove fatal in some cases.

"We are consuming more soft drinks than ever before and a number of health issues have already been identified including tooth problems, bone demineralisation and the development of metabolic syndrome and diabetes," said Dr Moses Elisaf, from the University of Ioannina in Greece, who led an academic review of the issue.

"Evidence is increasing to suggest that excessive cola consumption can also lead to hypokalaemia, in which the blood potassium levels fall, causing an adverse effect on vital muscle functions." His study, published in the International Journal of Clinical Practice, detailed cases where patients drank two or more litres of cola a day.

In one case, a 21-year-old pregnant woman was admitted to the hospital suffering tiredness, loss of appetite and repeated vomiting. The patient had consumed more than three litres of cola per day for the previous six years and was found to be suffering from severe hypokalaemia and a heart blockage.

Once she was taken off cola and given potassium replacement substances, she made a full recovery.

Other case studies of people drinking between two and nine litres of cola a day found they suffered muscle problems ranging from "mild weakness to profound paralysis".

The authors said their findings were relevant because we now live in an era when the food industry sells drinks in large sizes.

One theory is that the sugar content of cola could lead the kidneys to excrete too much potassium, while another is that the caffeine content of cola leads to a redistribution of potassium in the body's cells or increased excretion from the body.

The most common ingredients in cola drinks are glucose, fructose and caffeine, Dr Elisaf said.

"The individual role of each of these ingredients in the pathophysiology of cola-induced hypokalaemia has not been determined and may vary," he added. "However, in most of the cases we looked at for our review, caffeine intoxication was thought to play the most important role.

"This has been borne out by case studies that focus on other products that contain high levels of caffeine but no glucose or fructose. Despite this, caffeine-free cola products can also cause hypokalaemia because the fructose they contain can cause diarrhoea."