You need magnesium for strong bones and teeth, a healthy immune system, blood sugar regulation, heart function, energy metabolism, nerve and muscle function, and protein synthesis. Magnesium also helps regulate the levels of various other vitamins and minerals in your blood. However, some forms of supplemental magnesium are better absorbed than others.
Consuming foods rich in magnesium is the best way to meet your recommended magnesium intake. However, if you can't meet the recommended intake from food alone, different supplements are available. Magnesium lactate and magnesium chloride are better absorbed than magnesium oxide. Magnesium gluconate is also well absorbed. Time-release forms of magnesium might be better absorbed, as might forms that do not have enteric coatings.
Food sources of magnesium include dark green leafy vegetables, avocados, dried apricots, bananas, nuts, seeds, beans, peas, whole grains and soy. Meat, milk and hard water also contain some magnesium. Besides magnesium supplements, you can also get magnesium from certain laxatives and antacids in the form of magnesium hydroxide or magnesium sulfate. For those with very low magnesium levels, intravenous magnesium might be needed to raise magnesium levels back to normal.
The RDA for women between 19 and 30 is 310 mg per day, and women 31 and older should consume 320 mg per day. Men between 19 and 30 should consume 400 mg per day, and men 31 and older should consume 420 mg per day. Adults should get no more than 350 mg per day of their magnesium intake from supplements, as this is the tolerable upper intake level for supplemental magnesium.
Magnesium intake from food is unlikely to cause toxicity symptoms, so aim to get most or all of your magnesium from foods. If you have kidney or gastrointestinal problems, suffer from alcoholism or poorly-controlled diabetes, or take certain diuretics or antibiotics, you might need more magnesium to prevent deficiency symptoms. Taking B vitamins with magnesium might help increase magnesium absorption.