Sooner or later almost everyone gets a muscle cramp - also known as a "charley horse." These sudden, painful knots are due to a muscle spasm, and most often affect the back of the lower leg (the calf), the hamstring muscles in back of the thighs or the quadriceps muscles in the front of the thighs. The cramps may be only momentary or may last up to 15 minutes or longer, and some recur before subsiding.
No one knows why these muscle cramps occur, although one theory holds that they're due to inadequate stretching and muscle fatigue. Sometimes cramps are brought on by physical activity in extreme heat, which can lead to dehydration and depletion of salt and minerals (such as potassium, magnesium and calcium) through excessive perspiration. As we get older, we're more vulnerable to cramping because of the muscle atrophy that begins to occur in the mid 40s and worsens if you're inactive. In addition, circulation problems due to narrowing of the arteries can lead to cramps in your legs and feet. Cramps that occur at night may be caused by inactivity and smoking as well as impaired circulation and low levels of the minerals mentioned above. Pregnancy can also give rise to leg cramps at night as can medical conditions such as hypothyroidism, kidney failure, Addison's Disease, and peripheral neuropathy (usually a result of diabetes).
To prevent cramps, it is important to keep your body well hydrated. That means drinking plenty of liquids, especially during hot weather and during physical activity. Stretching exercises can help prevent cramping - the Web site of the American Academy of Orthopaedic Surgeons (orthoinfo.aaos.org) provides a description of useful calf, hamstring and quadriceps stretches.
For women, I also recommend trying a combination of 500-700 mg of calcium and half that amount of magnesium divided into several doses throughout the day and one before bed. Make sure you eat plenty of potassium-rich foods such as bananas, tomatoes, potatoes, broccoli, cantaloupe, oranges and grapefruit. You may also want to consider having your iron levels checked, as low levels can contribute to leg cramps, especially at night. Warm baths can help ease cramps, and both massage and acupuncture are worth exploring. If you smoke, stop now. And, in addition to stretching, try to get regular exercise.
Andrew Weil, M.D.