Ruth Rivett-Cuthbert, of East Taieri, asks :-

Although I take magnesium daily I still get cramp in my legs at night – to the extent that sometimes I have to go out to the kitchen and have a “wet finger-tip” of salt which makes the cramp go away. Why does salt taken in this manner work for cramp? In this day and age of processed food and high salt content of so many foods, I add only a small amount to cooking for flavour enhancement. Maybe not enough?

Phil Sheard, a physiologist at the University of Otago's School of Medical Sciences, responded.

Cramp is a powerful unplanned muscle contraction. It is often painful and may last from a few seconds to many minutes. Particularly intense episodes can leave the muscles feeling tender and sore for days afterwards.

Cramps are slightly more common in females (especially during pregnancy) than males and are more likely when undergoing strenuous physical activity, especially in a hot environment. Cramps are not usually an indication of any serious underlying medical condition, most people experience cramps at some stage in their life.

Leg cramps at night are very common, especially in older people. The precise causes are often unclear, but dehydration, low levels of electrolytes (sodium potassium, magnesium, calcium), and long periods of sitting (or bent leg/foot posture in bed) are common contributing factors. Cramps are often relieved and reduced in severity by stretching the affected muscle, and a simple common treatment and preventative is to ensure adequate hydration and electrolyte intake.

The act of getting up and walking to the kitchen may contribute to the relief provided (by stretching affected muscles), but if the salt works then ensuring adequate hydration, perhaps with a drink containing electrolytes may help. Low sugar electrolyte drinks are widely available, and for those who dont find these drinks palatable or desirable an alternative might be to make up one of the inexpensive powdered fruit drinks (choose your own flavour with or without sugar) and add about a quarter to half a teaspoon of salt per litre of drink. As always, moderation is important.