An essential mineral, magnesium is involved in blood glucose control, blood pressure regulation, muscle and nerve function, and protein synthesis.
When a person is deficient—as an estimated 56 to 75 percent of Americans are—the effects can be widespread, causing symptoms as varied as fatigue, loss of appetite, seizures, abnormal heart rhythms, and even personality changes. Even if someone isn’t deficient, low levels of magnesium can affect a variety of bodily systems.
Sleep. Magnesium regulates the nervous system, particularly the neurotransmitters that pass information back and forth from the body to the brain. It promotes relaxation, which improves the ability to fall asleep faster and obtain better sleep quality.
Asthma. By relaxing the bronchial muscles and widening the airways, magnesium can alleviate asthma symptoms. It is not a first-line treatment, but adding a magnesium supplement to traditional asthma medications can help prevent acute asthma attacks.
Anxiety and depression. Magnesium has a vital role in the healthy functioning of the brain. There’s a link between low magnesium levels and anxiety, which suggests that taking a supplement may ease anxiety. A cross-sectional study of close to 20,000 people published in 2019 reported that people who had more magnesium in their diets had lower rates of depression.
Type 2 diabetes. Magnesium is essential for insulin metabolism and glucose control. Research has shown that most diabetics suffer from magnesium insufficiency and that magnesium helps manage the disease by improving insulin sensitivity. A meta-analysis published in the Journal of Internal Medicine in 2007 found that a 100 milligram (mg) per day increase in total magnesium intake decreased the risk of diabetes by 15 percent.
Blood pressure. Adequate daily magnesium intake from food or supplements can decrease systolic and diastolic blood pressure in people who have both high blood pressure and magnesium deficiency. When blood vessels are narrowed or constricted, blood pressure rises, but magnesium reduces that constriction, allowing the blood to flow more freely. One meta-analysis of 22 studies concluded that magnesium supplementation decreased systolic blood pressure by 3 to 4 mmHg and diastolic blood pressure by 2 to 3 mmHg.
That may be why researchers found that people with serum magnesium levels in the highest quartile of normal (at least 0.88 millimoles per liter [mmol/L]) had a 38 percent lower risk of sudden cardiac death than people with levels in the lowest quartile (0.75 mmol/L or less).
Osteoporosis. The National Institutes of Health reports that women with osteopenia and osteoporosis have lower serum magnesium levels than women without those conditions, suggesting that magnesium deficiency might be a risk factor for osteoporosis. Furthermore, several studies suggest a positive correlation between magnesium intake and bone mineral density in both men and women.
Migraine headaches. A review of three placebo-controlled studies found that 600 mg per day of supplemental magnesium led to a small reduction in migraine frequency. The American Headache Society and the American Academy of Neurology note that magnesium supplementation should be considered for migraine prevention because evidence suggests that it is “probably effective.”
The strongest evidence has been found in people who experience migraine auras and in women who have menstrual-related migraines.
The recommended dietary allowance for magnesium depends on age and sex. Women need about 310 mg each day when they are between 19 and 30 years old, and 320 mg after age 31. Men should aim for 400 mg through age 30, then bump up to 420 mg. A wide variety of foods are excellent sources of magnesium. (See the box above.)
You can also take a supplement. Magnesium supplements come in different forms, and absorption and bioavailability vary by type. Opt for magnesium citrate when available. If not, look for magnesium lactate and magnesium chloride, both of which are absorbed better than magnesium oxide and magnesium sulfate.
Prolonged soaking in Epsom salts may also increase magnesium levels in the blood.
The most common side effect of magnesium supplementation is diarrhea. In fact, magnesium can also be used as a treatment for constipation. High doses can cause nausea and abdominal cramping. Very large doses (more than 5,000 mg/day) have been associated with magnesium toxicity, which can cause hypotension, nausea, vomiting, flushing, urine retention, depression, muscle weakness, difficulty breathing, irregular heartbeat, and cardiac arrest.
Before taking a magnesium supplement, talk to your doctor about potential medication interactions. Magnesium can decrease the absorption of oral bisphosphonates, such as alendronate (Fosamax), so they should be taken at least two hours apart. Similarly, if you’re taking a tetracycline antibiotic, such as demeclocycline (Declomycin) and doxycycline (Vibramycin), or a quinolone antibiotic, such as ciprofloxacin (Cipro) and levofloxacin (Levaquin), take the magnesium two hours before the antibiotic.
