Magnesium is naturally present in a variety of foods, available as a supplement, and an ingredient in antacids and laxatives. The mineral plays an important role in assisting more than 300 enzymes to carry out various chemical reactions in the body such as building proteins and strong bones, and regulating blood sugar, blood pressure, and muscle and nerve functions. Magnesium also acts an electrical conductor that contracts muscles and makes the heart beat steadily.
More than half of the magnesium in our body is stored in bones, and the remaining in various tissues throughout the body.
RDA: The Recommended Dietary Allowance (RDA) for adults 19-51+ years is 400-420 mg daily for men and 310-320 mg for women. Pregnancy requires about 350-360 mg daily and lactation, 310-320 mg.
UL: The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for magnesium is 350 milligrams from supplements only. High-dose supplements can lead to diarrhea, nausea, and cramping in some people. Extra magnesium from food is safe because the kidneys will eliminate excess amounts in urine.
Magnesium and Health
Magnesium is a key factor in making several parts of the body run smoothly: the heart, bones, muscles, nerves, and others. Without enough magnesium, these areas malfunction. This is summarized in research, which finds that a magnesium deficiency or low magnesium diet leads to health problems. Although epidemiological studies show that higher magnesium diets are associated with lower rates of disease, results are mixed from clinical trials showing that magnesium supplementation can correct these conditions. It may be because a magnesium-rich diet is often higher in other nutrients, which collectively work together in disease prevention as opposed to a supplement containing a single nutrient.
For disease prevention, a good rule of thumb is to eat a daily diet that includes some magnesium-rich foods and take a supplement if directed by a physician to correct a deficiency if blood levels are low.
Magnesium is a component of bone; in fact 60% of the body’s magnesium is stored in bone. It is also involved with the activity of bone-building cells and the parathyroid hormone, which regulates calcium levels. Population studies have found an association of greater bone mineral density in men and women with higher magnesium diets.  A cohort study of 73,684 postmenopausal women from the Women’s Health Initiative found that a lower magnesium intake was associated with lower bone mineral density of the hip and total body, although the authors cautioned that their finding did not translate into an increased risk of fractures.  A meta-analysis of 24 observational studies examining fracture risk did not find that higher magnesium intakes were associated with a reduced risk of hip and total fractures.  Clinical trials have shown mixed results with the use of magnesium supplements to increase bone mineral density. More research is needed to see if and how much of a supplement can reduce fracture risk.
Magnesium is sometimes prescribed as a complementary treatment for migraine headaches, as clinical studies have found low magnesium levels in people suffering from this condition.  Randomized double-blind controlled trials have found that magnesium citrate and magnesium oxide supplements (about 500 mg/day) taken for up to 3 months were protective against migraines.  In a randomized double-blind clinical trial, 70 patients who were admitted to the emergency room with acute migraine headache were given either the usual IV treatment for migraine (dexamethasone/metoclopramide) or IV magnesium sulfate. The study found the magnesium to be more effective and faster-acting than the typical treatment. This was a one-time administration in an acute setting, so studies with longer follow-up are needed to confirm this benefit.
The National Headache Foundation suggests a daily dose of 400-600 mg of magnesium to reduce the frequency of migraine attacks; however because this is greater than the RDA, it may lead to side effects (e.g., muscle weakness, diarrhea) in some people and may not be safe with certain medical conditions. They recommend discussing the use of high-dosage magnesium supplements with a physician.
Magnesium assists with neurological pathways that, when not functioning correctly, are believed to lead to mood disorders like depression and anxiety. Several observational studies have linked lower magnesium levels with increased depression. [6,7] However, a small number of randomized clinical trials have not shown consistent results that magnesium supplementation is an effective treatment for depression.  The control groups in these trials, either given a placebo or an antidepressant medication, showed similar effects as the treatment group receiving magnesium supplements. The trials also tended to have a small number of participants with a short duration, ranging from 1-8 weeks. Longer trials with standardized depression rating scales are needed to better assess this connection.
Cardiovascular disease (CVD)
High blood pressure is a risk factor for cardiovascular disease (CVD), and magnesium helps to regulate blood pressure. Studies have shown an association with magnesium deficiency and high blood pressure. However, the results of clinical studies are mixed on using magnesium supplements to lower blood pressure. Epidemiological studies have found an association of the DASH diet (including magnesium-rich fruits, vegetables, and low-fat dairy products) with decreased blood pressure, but DASH is also rich in potassium and calcium that may lower blood pressure, so it is not clear if magnesium or a combination of nutrients is protective. Other population studies have shown that higher magnesium intakes and/or higher blood levels of magnesium are associated with a lower risk of stroke and deaths from heart disease, although again it is difficult to separate out other nutrients in these same foods that are protective against CVD. 
Type 2 diabetes
Magnesium assists enzymes that regulate blood sugar and insulin activity. Prospective cohort studies show an association of diets low in magnesium with an increased risk of type 2 diabetes.  However, the results are mixed in clinical trials of magnesium supplements for people with diabetes, some finding an improvement in insulin sensitivity when correcting a magnesium deficiency, and others showing no change. Results are also mixed on the effectiveness of supplements in improving overall blood sugar control. Part of the reason may be differences in the study design of these clinical trials. The American Diabetes Association reports a lack of evidence at this time to recommend magnesium supplements to improve blood sugar control in people with diabetes. 
- Almonds, peanuts, cashews
- Pumpkin seeds
- Peanut butter
- Beans (black, kidney)
- Soybeans, soymilk
- Cooked spinach, Swiss chard
- White potato with skin
- Brown rice
- Oatmeal (instant, whole oats)
- Dark chocolate (at least 70%)
- Milk, yogurt
A magnesium supplement may be prescribed if the body is having problems absorbing the nutrient. Over-the-counter magnesium supplements come in different forms; liquid types like magnesium citrate or chloride may be better absorbed than solid tablets like magnesium oxide and sulfate.
Magnesium can have a laxative effect at high doses; in fact, it is sold as a laxative in the form of magnesium hydroxide. Magnesium hydroxide is also an ingredient in some popular antacids to treat heartburn and upset stomach; it is important to be aware of the laxative effect when using magnesium hydroxide tablets for an upset stomach.
Signs of Deficiency and Toxicity
Although magnesium is naturally found in a variety of foods and some fortified foods, national dietary surveys show that most Americans of all ages eat less than recommended amounts.  However, these deficiency levels are marginal and not likely to produce symptoms. The body also helps to preserve magnesium levels when stores are low by limiting the amount excreted in urine and absorbing more magnesium in the gut. 
A true deficiency occurs with a long-term low magnesium diet, malabsorption, and large losses from alcohol abuse or use of medications that deplete magnesium (some diuretics, proton pump inhibitors, and antibiotics).
- Signs of deficiency include:
- Fatigue, weakness
- Poor appetite
- Nausea, vomiting
- Numbness or tingling in skin
- Muscle cramps
- Abnormal heart rate
- Risk factors for deficiency include:
- Alcohol abuse. A long-term excessive intake of alcohol is associated with a poor diet low in magnesium, digestive upset that leads to malabsorption, and problems with various organs that can flush out too much magnesium through urine.
- Older ages. The elderly have lower magnesium intakes according to national dietary surveys. Aging also causes decreased absorption of magnesium in the gut and increased excretion in urine. Furthermore, older adults are more likely to be on medications for chronic diseases that can lower magnesium stores.
- Conditions with malabsorption. Diseases that interfere with digestion can lower the amount of magnesium absorbed. Most magnesium is absorbed in the largest segment of the small intestine, the ileum, which may be compromised in conditions like celiac and Crohn’s disease. Surgery that removes the ileum, which is sometimes needed with colon cancer, ulcerative colitis, or Crohn’s disease, further adds to a deficiency risk.
- Type 2 diabetes mellitus. Insulin resistance or uncontrolled diabetes can cause the kidneys to make extra urine to rid the body of high levels of blood sugar. This increased amount of urine may also flush out magnesium.
Toxicity is rare from food sources because the kidneys will remove excess magnesium in the urine. However toxic levels may occur with long-term use of high-dosage supplements. People with kidney disease have a higher risk of toxicity because their kidneys are not working properly and cannot flush out extra magnesium.
- Signs of toxicity include:
- Nausea, vomiting
- Low mood, depression
- Muscle weakness
- Low blood pressure, abnormal heartbeat
- Heart attack
Did You Know?
Magnesium supplements are a popular remedy for leg and foot cramps, a bothersome condition that may jolt you awake in the middle of the night or during exercise. A deficiency of magnesium can certainly cause muscle cramping, but these supplements are often used whether or not people know they are truly deficient.
Evidence so far does not support this treatment for muscle cramps. A Cochrane review of seven randomized controlled trials looking at the effects of magnesium supplements on muscle cramps did not find a significant difference in intensity or duration of cramps in people using the supplements versus a placebo for one month.  Information was not available on the participants’ blood levels of magnesium at the start of the trials, so it is not known if the muscle cramps were related to a deficiency versus other factors.
- National Institutes of Health Office of Dietary Supplements: Magnesium Fact Sheet for Health Professionals https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/. Accessed 9/2/2019.
- Orchard TS, Larson JC, Alghothani N, Bout-Tabaku S, Cauley JA, Chen Z, LaCroix AZ, Wactawski-Wende J, Jackson RD. Magnesium intake, bone mineral density, and fractures: results from the Women’s Health Initiative Observational Study. Am J Clin Nutr. 2014 Apr;99(4):926-33.
- Farsinejad-Marj M, Saneei P, Esmaillzadeh A. Dietary magnesium intake, bone mineral density and risk of fracture: a systematic review and meta-analysis. Osteoporos Int. 2016 Apr;27(4):1389-1399.
- Gröber U, Schmidt J, Kisters K. Magnesium in Prevention and Therapy. Nutrients. 2015 Sep 23;7(9):8199-226
- Volpe SL. Magnesium in disease prevention and overall health. Adv Nutr. 2013 May 1;4(3):378S-83S.
- Tarleton EK, Littenberg B. Magnesium intake and depression in adults. J Am Board Fam Med. 2015 Mar-Apr;28(2):249-56.
- Kirkland AE, Sarlo GL, Holton KF. The Role of Magnesium in Neurological Disorders. Nutrients. 2018 Jun 6;10(6).
- Evert AB, Boucher JL, Cypress M, Dunbar SA, Franz MJ, Mayer-Davis EJ, Neumiller JJ, Nwankwo R, Verdi CL, Urbanski P, Yancy WS Jr. Nutrition therapy recommendations for the management of adults with diabetes. Diabetes Care. 2013;36:3821-42.
- Moshfegh A, Goldman J, Ahuja J, Rhodes D, LaComb R. What We Eat in America, NHANES 2005-2006: Usual Nutrient Intakes from Food and Water Compared to 1997 Dietary Reference Intakes for Vitamin D, Calcium, Phosphorus, and Magnesium. U.S. Department of Agriculture, Agricultural Research Service. 2009. https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/0506/usual_nutrient_intake_vitD_ca_phos_mg_2005-06.pdf. Accessed 9/2/2019.
- Garrison SR, Allan GM, Sekhon RK, Musini VM, Khan KM. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2012 Sep 12;(9):CD009402.
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