One of the most important minerals is one that most of us aren't paying attention to – and around half of the population is lacking. Magnesium is key for heart health, sleep, and keeping stress at bay and muscles healthy. Yet a raft of studies point out that we aren't getting enough of it, and this may cause insomnia, anxiety, and high blood pressure. "So many patients and doctors are unaware that a deficiency in a simple mineral can lead to so many problems," says Dr. Dennis Goodman, Clinical Assoc. Professor of Cardiology at NYU, Director of Integrative Medicine at the New York Medical Associates, and author of a new book, 'Magnificent Magnesium.' "Some of these, like muscle cramps, are nuisances, but others are major – we're talking diabetes, obesity, heart attacks, and strokes."

Magnesium helps regulate cortisol (too much can lead to anxiety), melatonin (essential for sleep), and blood pressure, and provides the energy to contract and relax the heart and other muscles. Low magnesium levels can lead to symptoms like exhaustion, irritation, and sleeplessness. "If you feel fatigued or irritable, or you're having muscle twitches or weakness, those are all symptoms of possible low magnesium," says Dr. Gregg C. Fonarow, a professor of cardiovascular medicine at UCLA's medical school. Goodman recommends everyone get tested with a simple red blood cell magnesium test that can be added to a routine blood test by your primary doctor.

Many Americans are magnesium deficient because we eat so many fried and refined foods, processed in a way that strips out the mineral. But those of us who eat well may have trouble getting enough, too: Foods richest in magnesium, like green leafy vegetables, have lower levels when grown with chemical fertilizers. Antibiotics, beta-blockers, and other prescription medications decrease reserves as well. Even diuretics taken for high blood pressure – which itself can be a sign of low magnesium – can drain your body of the nutrient that helps to regulate your blood flow.

Researchers are beginning to pay more attention to magnesium levels for cardiovascular health, says Dr. Liana Del Gobbo, of the Harvard School of Public Health. Del Gobbo recently published a study showing that having more magnesium in the diet can cut overall heart risk (including heart attack and stroke) by up to 22 percent. "Dietary cholesterol has been overemphasized as the main heart health concern," she says, adding that a magnesium test should be part of the prevention.

If you find that your levels are low, you can usually get balanced with supplements and changes to your diet. "If you're deficient, I suggest taking magnesium supplements first," says Goodman. The National Institutes of Health recommends at least 400 milligrams a day of magnesium for men, but Goodman advises a more specific regimen for those who have low levels: about five milligrams per pound of body weight. "If you then change your diet to include more leafy green vegetables, nuts, and whole grains, you can take yourself off the supplements." Our need for magnesium also gives us another reason to avoid processed foods. "It's as easy as eating whole wheat instead of refined flour, which has 85 percent of the magnesium stripped out." says Andrea Rosanoff, director for the Center for Magnesium Education and Research in Pahoa, Hawaii. 

How to Get Extra Magnesium

In 'Magnificent Magnesium,' Dr. Goodman suggests the average person get three milligrams a day for every pound they weigh – or 540 milligrams for an 180-pound man. If you're deficient, bump that up to five milligrams per pound. Here is his advice on how to get all that magnesium.

If your levels are normal . . . 

Eat for magnesium. Good sources include spinach (269 milligrams for one bunch), almonds (124 milligrams for half a cup), dark chocolate (237 milligrams for one bar), and fish (106 milligrams for a salmon fillet).

Buy local and organic. The amount of magnesium in plants varies with soil quality. Organic farms use less fertilizer – meaning there's more magnesium in their veggies.

If your levels are low . . . 

Take a supplement. "Aim for magnesium that ends in -ate," says Goodman – magnesium citrate, chelate, malate, and sulfate, which are better absorbed than magnesium hydroxide. Diarrhea can be a side effect of magnesium supplements, so opt for slow-release pills, or lower your dose if symptoms continue.

If stressed, up your intake. Low magnesium can lead to stress and anxiety, which can further deplete your levels.

Watch out for drug interactions. Magnesium can interact with a number of drugs, including antibiotics and blood pressure medication. Talk to your doctor and take magnesium supplements more than two hours before any medication.