Take note: the focus should be on getting magnesium from foods, not supplements. As the researchers warn: "your body absorbs magnesium from food differently than it does from supplements". From CNN:
Magnesium, an invisible deficiency that could be harming your health
Feeling exhausted? Or noticing weird muscle cramps that are throwing off your workouts? You might be suffering from a magnesium deficiency. Dubbed the "invisible deficiency" by some experts because it's so hard to spot and diagnose, magnesium deficiencies are more dangerous than you might think. "Magnesium is involved in over 300 biochemical reactions in your body. It affects everything from your heartbeat to your muscles to your hormones," says Dr. Danine Fruge, Associate Medical Director at the Pritikin Longevity Center in Miami, Florida.
"Studies have shown that only about 25% of U.S. adults are at or above the recommended daily amount of 310 to 320 milligrams for women and 400 to 420 for men," says Fruge. In fact, the 2005-2006 National Health and Nutrition Examination Survey (NHANES) revealed that at least half of the U.S. population had inadequate intakes of magnesium.
Loss of appetite, nausea, fatigue -- the initial symptoms of magnesium deficiency are also common side effects of other health conditions, making it difficult to diagnose. This sneaky disorder manifests in three different stages, depending on how lacking you are in the nutrient. While initially symptoms can be minor, a magnesium deficiency may eventually cause noticeable problems with your muscle and nerve function such as tingling, cramping, numbness and contractions (like that annoying eye twitch you just can't shake). In its worst stages, magnesium deficiency could even cause seizures, personality changes, or abnormal heart rhythms.
To make matters scarier, this condition can be difficult to detect with medical tests. Since only 1% of magnesium is found in your blood (most is in your bones or organs), a simple needle prick often won't help determine your levels. Instead, Fruge says diagnoses are usually made through process of elimination and by examining a patient's lifestyle.
It may be what you're eating — rather than what you're not eating — that's putting you at risk for magnesium deficiency. "It's very easy to get enough magnesium. I think the reason so many people are deficient is because a lot of food and drink can make magnesium unavailable to their bodies," says Fruge. The main culprits: soda, caffeinated beverages and alcohol, according to Fruge... Consuming too much alcohol can interfere with your body's absorption of vitamin D, which aids magnesium absorption. As for food, refined sugar causes the body to excrete magnesium through the kidneys, resulting in a net loss, according to Fruge.
Plus, your body absorbs magnesium from food differently than it does from supplements. You should only use magnesium supplements under the direction of a doctor — and be sure not to exceed 350 non-food milligrams of magnesium per day (unless a medical professional instructs you differently). "Your body has built-in mechanisms that don't allow it to overdose from food, but that doesn't exist for supplements. Too much magnesium via supplement can put your heart into an arrhythmia and that can even be fatal, particularly for people with issues like diabetes," says Fruge.
Food sources are your safest bet so focus on amping up your consumption of leafy greens — one cup of cooked spinach provides 157 milligrams of magnesium. Legumes are a solid choice too, with a cup of cooked white beans coming in at 113 milligrams of the nutrient. And if you're a fan of squash and pumpkin seeds, one cup packs in a whopping 649 milligrams. Other great options are nuts, including almonds and cashews, most types of fish, and whole grains.