Magnesium—like Vitamins D and B before it—is the supplement du jour. It's among the top ten most popular dietary supplements and for good reason. Chances are you're low on the fourth most abundant mineral in the body—nearly half of all Americans are. But do you need to take a supplement? And if so, which one? Sit tight. We've got your magnesium questions answered.

What is Magnesium?

Magnesium is found in bones, teeth, and red blood cells, and plays a key role in some 300 chemical reactions in the body.

"Magnesium plays a critical role in maintaining normal muscle, heart, and nerve function, promoting a healthy immune system, and maintaining the strength and health of your bones," Erin Palinski-Wade, R.D., author of 2 Day Diabetes Diet told Shape.

Research has found that about half of Americans don't get enough magnesium in their diet. "Magnesium deficiency in the short term can cause sleep disturbances, muscle cramps, and a loss of energy," says Palinski-Wade. "Long term, it may cause blood pressure to rise and weaken bones, increasing the risk of developing osteoporosis."

Do You Need a Magnesium Supplement?

While many people aren't getting enough magnesium through diet alone, it's rare to have a true deficiency and you have your kidneys to thank. Dr. Bruce Bistrian, chief of clinical nutrition at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School, says magnesium deficiency in otherwise healthy individuals is rare: "The kidney has an extraordinary ability to reduce magnesium loss in urine, and thus achieve magnesium balance on a wide variety of intakes," he said.

But some people are at increased risk of magnesium deficiency, and chronic medical conditions are often the culprit. "The people at highest risk for low magnesium are those with diarrhea and other forms of malabsorption like Crohn's disease and celiac disease," Shanna Levine, MD, assistant clinical professor at the Icahn School of Medicine at Mount Sinai told Health. Those who regularly abuse alcohol may also be at risk for low levels of magnesium. To make matters worse, magnesium is also depleted by stress, making the idea of taking a supplement seem prudent for most of us.

Which Kind of Magnesium Should You Take?

Reduce stress and improve sleep: magnesium glycinate

"Magnesium Glycinate is bound to the amino acid glycine," Nutritionist Adrienne Dowd, RD, of Parsley Health told Well + Good. "It has increased bioavailability and has a calming effect. It can be used for relaxation, increased sleep quality, and stress relief." It has also been used to help with with PMS, fibrocystic breasts, sleep, anxiety, cravings, pains, and cramps.

Improve digestion: magnesium citrate

"This type of magnesium is bound to citric acid, which allows for an easier absorption and has a gentle laxative effect," Dowd says.

Increase energy: magnesium malate

For those having issues with energy production, a magnesium malate supplement may be effective for helping with chronic fatigue syndrome and/or fibromyalgia.

Improve learning and memory function: magnesium threonate

This form of magnesium was created to cross the blood-brain barrier and may improve learning and memory functions. It also may help assuage age-related cognitive decline.

Treat heartburn: magnesium oxide

"Magnesium Oxide is less bioavailable and when bound with water to make magnesium hydroxide, it is generally used to alleviate heartburn and constipation—for example, Milk of Magnesia," Dowd said. She explains that Milk of Magnesia provides 500 mg of magnesium hydroxide (magnesium oxide, plus water) per tablespoon. "The directions recommend taking up to 4 tablespoons per day," Dowd said. "Although such a dose of magnesium is well above the safe upper level, some of the magnesium is not absorbed because of the medication's laxative effect."

Improve skin: magnesium chloride

"The skin is a great way to increase magnesium levels and bypass using the gut – this is especially beneficial for people with IBS (or leaky gut) who suffer from malabsorption of nutrients," said Magdalena of Hormones Balance. Dowd recommends a magnesium lotion — magnesium chloride in a base of coconut or shea butter — for muscle spasms or cramps, dermatitis, eczema, and acne."

Ease muscle aches: magnesium sulfate

"Magnesium sulfate is more commonly known as epsom salts," Dowd says. "Epsom salt baths are great for muscle soreness, tightness, aches, and pains."

Fill Your Plate with Magnesium

It's difficult to assess magnesium status with a simple blood test. Furthermore, magnesium levels found in our food sources are declining due to high-yield farming practices that degrade the key minerals of the soil. Choosing organic produce can help mitigate this potential loss of essential minerals. A magnesium-rich diet includes: pumpkin seeds, sesame seeds, cashews, almonds, prunes, bananas, leafy greens, white beans, tofu, and black beans, halibut, tuna, quinoa, and buckwheat. In other words, there are plenty of choices.

The Takeaway

"Chronically low intakes of magnesium can induce changes in biochemical pathways that can increase the risk of cardiovascular disease, type 2 diabetes, osteoporosis, and migraine headaches," said Adrienne Dowd, RD, of Parsley Health. Cover your bases and chow down on pumpkin seeds, leafy greens, and black beans and pop a pill.