“Drinking large amounts of cola can cause paralysis,” reported The Daily Telegraph. It said that doctors have warned that muscle problems, an irregular heartbeat and even paralysis can be caused by drinking large amounts of cola. The newspaper said that chronic cola consumption can cause hypokalaemia, a condition in which patients have low levels of potassium in the blood.
The news report is based on a review of six case reports featuring people who drank excessive amounts of cola and developed hypokalaemia. More research is needed to establish whether drinking large amounts of cola can cause this condition.
It should be emphasised that these people drank three to 10 litres of cola a day for an extended period of time. Drinking such large amounts of sugar-rich soft drinks is known to raise the risk of diabetes, tooth erosion and obesity. At present, these should be considered as more likely and worrying effects of drinking such large amounts of soft drinks.
Where did the story come from?
The research was carried out by Dr Vasilis Tsimihodimos and colleagues from the Department of Internal Medicine at the University of Ioannina in Greece. The study was published in the peer-reviewed medical journal The International Journal of Clinical Practice.
What kind of scientific study was this?
This review investigated the rare, but potentially dangerous, side effect of hypokalaemia (low blood levels of potassium) caused by the consumption of large amounts of cola-based soft drinks. The authors searched for published case studies on the subject, and discussed its clinical significance and how it might occur.
To find suitable case studies, the researchers searched the database PubMed for instances of 'cola', 'hypokalaemia', 'potassium' and 'caffeine'.
They say that soft drink consumption has increased considerably over the last few decades and that cola-based soft drinks are now possibly the refreshment with the most sales worldwide. Concerns have been raised about the effects of colas on human health, including the softening of tooth enamel, the loss of bone minerals and diabetes mellitus. They say there is also some evidence that drinking large amounts of cola-based soft drinks over a long period of time may result in severe symptoms from low blood potassium.
What were the results of the study?
The literature search found six case reports published between 1994 and 2008. The case reports feature six individuals who developed problems after drinking three to 10 litres of cola a day for more than a month and a half (most cases sustained this intake for one to three years).
The six individuals included two pregnant women and four non-pregnant individuals. The first pregnant woman reported tiredness, a loss of appetite and recurrent vomiting. The 21-year-old woman had drunk more than three litres of cola a day for the past six years. She was found to have severe hypokalaemia (she had potassium levels of 1.9mmol/L when the level is usually above 3.5mmol/L) and a slow heartbeat. After stopping cola consumption and replacing the potassium in her blood she made a full recovery. The other pregnant woman reportedly suffered from muscular weakness and very low serum potassium levels.
The most common health complaints from the six case reports were muscular in origin and ranged from “mild weakness to serious paralysis”. All the individuals had abnormally low levels of potassium in the blood, which the authors say could not be attributed to other more common causes of hypokalaemia.
All six patients made a full recovery. The authors of the individual case reports mostly suggest caffeine intoxication to be the probable cause.
What interpretations did the researchers draw from these results?
The researchers say that it is well known that caffeine may result in severe hypokalaemia because the chemical moves potassium into cells and increases the excretion of potassium through the kidneys. They say that several other cases of hypokalaemia have been described in individuals consuming large amounts of other caffeinated drinks such as tea and coffee.
They say that there are important public health implications to their findings and, despite the full recovery of all patients so far, they say that chronic hypokalaemia clearly predisposes individuals to the development of potentially fatal complications such as cardiac arrhythmias (heart rhythm abnormalities). They propose that it may also be a cause of increased fatigue, loss of productivity and muscular symptoms that could vary from mild weakness to profound paralysis.
What does the NHS Knowledge Service make of this study?
This collection of case reports indicates that excessive cola consumption could possibly cause low blood potassium. However, these case reports were collected over 15 years and it is important to bear the following in mind:
- The authors do not give a clear description of how these reports were checked for quality, so it is not possible to comment on this. Other medical conditions that the patients may have had are not reported. In addition, the authors only searched one database for studies, so it is possible that other reports of this condition listed in other databases have been missed.
- Because only single case reports were identified, it is not clear how frequently people who consume similarly large amounts of cola experience these side effects. No comparison is made with people who consume large amounts of coffee or tea. If caffeine is the cause in these cases, the rates of hypokalaemia in coffee drinkers would also be of interest.
Further study is needed to establish if heavy soft drink consumption causes hypokalaemia. Muscle weakness and tiredness was a symptom for many of these patients, but the more concerning symptom of irregular or slow heartbeat was relatively rare. Fatal heart problems did not occur. This suggests that some of the news coverage of this study may be unnecessarily alarmist.
It should be emphasised that these individuals drank between three and 10 litres of cola a day for an extended period of time. The known effects of drinking such large amounts of sugar-rich soft drinks include diabetes, tooth erosion and obesity. At present, these should be considered as more likely and worrying effects of drinking such large amounts of soft drinks.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Guardian, 20 May 2009
The Daily Telegraph, 20 May 2009
The Mirror, 20 May 2009
BBC News, 20 May 2009
Links to the science
The international journal of clinical practice 2009; 63: 900-902
Cochrane Database of Systematic Reviews 2008, Issue 3.