Could your painkillers be giving you a heart attack? It's not certain, but it's possible.
The dispersible and effervescent formulations of the common over-the-counter analgesic paracetamol 500mg, for example, can contain a significant amount of sodium - an excess of which has been linked with a greater risk of heart attacks and strokes.
If you took the maximum daily dose of eight tablets of paracetemol a day, you'd exceed the recommended total daily allowance of sodium of 2.4 grams by as much as 40 per cent or more. And that's just from one drug, excluding the sodium you will consume through food.
In fact, researchers in Britain have found that patients who took sodium-containing drugs faced a 16 per cent higher risk of a heart problem or stroke, were seven times more likely to develop high blood pressure, and had a 28 per cent higher death rate.
"Curiously, unlike foods, pharmaceutical manufacturers are not placed under any restrictions or obligations with regards to sodium content or labelling of these sodium-containing formulations," wrote the researchers from the University of Dundee and University of College London in their study report published last week on the British Medical Journal website bmj.com
They said the public "should be warned about the potential dangers of high sodium intake from prescribed medicines", and that sodium-containing formulations "should be prescribed with caution only if the perceived benefits outweigh the risks".
They also called for the sodium content of medicines to be clearly labelled in same way foods are labelled.
In Hong Kong, as in Britain, "there are no specific labelling requirements for sodium content in registered pharmaceutical products", said the Health Department.
Asked about the possibility of making sodium labelling mandatory for pharmaceutical products in Hong Kong, the department replied: "The [department] shall keep in view of the international practice and development, and review the labelling requirements when necessary."
It's different in the US. Since 2004, drug manufacturers there are required to list sodium content on the label of prescription drugs and also have a warning label to alert people who are on sodium-restricted diets to consult their doctors before using products that contain more than 140 milligrams of sodium as the maximum daily dose.
Effervescent, dispersible and soluble versions of painkillers, vitamin supplements or other common medicines contain sodium for various reasons. The element can aid absorption of the medicine into the body; as sodium bicarbonate it makes tablets fizz; in other compound forms it can help disperse the medicine or dissolve it in water.
Many studies have shown that excess salt - also known as sodium chloride - is harmful to heart health. Eating too much salt contributed to 2.3 million deaths from heart attacks, strokes and other heart-related diseases globally in 2010, representing 15 per cent of all deaths due to these causes, according to research presented at an American Heart Association meeting this year.
Seventy-five per cent of the world's population consumes nearly twice the daily recommended amount of sodium. Global sodium intake from commercially prepared food, table salt, salt and soy sauce added during cooking averaged nearly 4,000mg a day in 2010. The World Health Organisation recommends limiting sodium to less than 2,000mg a day.
While the BMJ study researchers acknowledge that there is still some controversy regarding the link between dietary sodium and cardiovascular events, they say their findings "are potentially of public health importance".
In the study, 1.2 million British patients - taking either sodium-containing or non-sodium versions of the same drugs - were tracked for an average of just over seven years. During this time, more than 61,000 cardiovascular events occurred.
"Prescription of these sodium-containing formulations should be done with caution, and patients prescribed them should be closely monitored for the emergence of hypertension," said the researchers.