Magnesium deficiency

Magnesium keeps muscles, nerves and the heart working. True low blood magnesium is less common than the internet suggests, and usually has a clear cause: a medicine, alcohol or a bowel condition.

Symptoms

Mild deficiency usually causes nothing, or non-specific signs:

• muscle cramps, for example in the calves at night;
• muscle twitches, including an eyelid;
• tiredness and weakness;
• numbness or tingling.

An eyelid twitch is far more often stress, short sleep or coffee than magnesium.

Who is at risk

• years of stomach-acid reducers (omeprazole, pantoprazole and similar);
• diuretics (furosemide, torasemide, thiazides);
• metformin;
• heavy alcohol use;
• coeliac disease, Crohn’s disease, chronic diarrhoea, bowel surgery;
• age 65 or older;
• a diet low in greens, beans, nuts and whole grains.

Which test to ask for

Serum magnesium, usually with potassium and calcium, which often fall with it.

The main pitfall: less than one per cent of the body’s magnesium is in the blood; the rest is in bones and cells. A normal result does not rule out deficiency, so a doctor reads it alongside your medicines and symptoms.

What not to do

Do not take magnesium on your own if you have kidney disease: the kidneys cannot clear the excess. Magnesium also reduces the absorption of levothyroxine and some antibiotics. If you take medicines, ask a doctor or pharmacist first.