The manufacturers of mattress magnets claim that their magnetic mattress pads radiate a soothing "sleep field" that increases circulation and relieves joint and muscle pain. Although I was once skeptical, mattress magnets really do have demonstrable health effects.
About 10 years ago I worked on a project for the late renowned cardiologist Demetrio Sodi-Pallares (1913-2003). Dr. Sodi, as we called him, devoted much of the last 30 years of his medical practice to treating hopeless cases for free in a home office he had constructed, to his wife's considerable chagrin and requiring his pull with the local zoning authorities, over his swimming pool and front yard. Prior to running his own free clinic, Dr. Sodi had been a professor at UCLA, Michigan, and Baylor, and had published over 300 papers in the medical literature.
One of the doctor's most effective tools, as early as 1965, was in fact a magnetic mattress--made to exacting specifications under the supervision of an electrical engineer he had full time on his staff. (Dr. Sodi was not financially challenged.) As he documented in his books, and to me personally, daily treatment with a magnetic mattress not only could increase circulation, in some cases it was part of an effective cure of angina or congestive heart failure.
But not when used by itself.
The key to success with the magnetic mattress, Dr. Sodi discovered, was to have a compatible electrolyte balance in the bloodstream. In most cases, this meant a low-salt diet. For reasons Dr. Sodi did explain in a 300-page treatise and in several publications (and in a therapy approved by the American Heart Association in 1998), magnet therapy works better when cells aren't electrically discharged by sodium.
How does that work?
Every cell in the human body has a slight (-4 mV to -90 mV) charge across its outer membrane. The negative charge helps it attract positively charged electrolytes and proteins; negatively charged nutrients generally require an active transport process. Salt releases positively charged sodium ions (and negatively charged chlorine ions that are preferentially excreted). Too much positive charge and there's a stress on the cell. Remove the electrical stress on the cell, Dr. Sodi believed, and magnet therapies can work optimally.
So, if you're going to invest in a magnetic mattress, particularly if you're going to spend a couple thousand dollars on a fully magnetic system built into your mattress, amplify your chances of success with a low-sodium diet. Avoid cheese, pickles, canned foods, and smoked meats and fish. Get plenty of potassium from fruits and vegetables. Your dietary discipline will be rewarded with a far more noticeable effect from magnet therapies.