What causes leg cramps?

Every weekday, a CNNHealth expert doctor answers a viewer question. On Wednesdays, it's Dr. Otis Brawley, chief medical officer at the American Cancer Society.

Asked by Cleester of Bloomfield Hills, Michigan

I am generally a very healthy woman. I frequently wake up at night with painful cramps in the thighs and the back of my legs below the knee. What causes cramps and how can I get rid of them?

Expert answer

Dear Cleester,

Cramping is painful contracture of muscles. It generally lasts for five to 10 minutes and then remits. It can awaken someone from a sound sleep.

Cramping of the legs and feet is very common. Cramping in the hands and arms is seen but less common.

This condition is seen in children or adults of any age. People who have cramping regularly should be seen by a health care provider, even though the cause is often never found after extensive evaluation.

When the cause is found, cramping can be due to prolonged sitting or leg position during sedentary activity.

Perhaps most commonly, cramps can be due to overuse of muscles that are not accustomed to exercise.

The second most common cause is dehydration. Cramps can also be caused by electrolyte and metabolic disorders. Diuretic drugs can commonly cause cramping through dehydration, sodium or potassium depletion.

Parathyroid disease causes high or low calcium levels and is associated with cramping, as is thyroid dysfunction. Parathyroid and thyroid diseases are perhaps a more common cause of cramping in the hands and arms compared with other causes of cramping.

The evaluation of cramping will commonly involve a drug history and blood studies checking sodium, potassium, magnesium and calcium levels as well as thyroid function tests.

The physical examination is usually normal in a patient with routine cramping. The health care provider will also be trying to distinguish common cramping from muscle diseases that can mimic it and be an uncommon side effect of commonly prescribed drugs used to lower cholesterol (such as cholestyramine) or decrease stomach acid (cimetidine or ranitidine).

Decreased oxygenation of leg muscles due to peripheral vascular disease and the pain of diabetic neuropathy can also be mistaken for cramps. Leg cramps are best prevented with nondrug treatments.

Daily stretching and muscle strengthening can be very useful in preventing cramps. Stretching the muscle group during the cramp attack can be helpful in relieving it.

Chloroquine or the similar compound quinine (an ingredient of tonic water) has been prescribed to prevent cramping. Chloroquine has recently fallen out of favor.

Calcium channel blockers have become the preferred first medical treatment for cramping in patients who get them often for unknown reasons.

A few people find that a daily dose of vitamin B complex prevents cramping.