Nutrition Basics: Many Roles of Magnesium


Since we’ve covered all of the macronutrients, we’re moving onto the micronutrients. And we’re starting with the minerals because so many of us are deficient in them. (Women, especially, are familiar with the need for calcium, but the other minerals are just as important and often lacking as well!)

Magnesium makes up ~1% of body weight. Most of it (~55%) is found in bones, with an additional ~25% found in the skeletal muscle cells and ~20% in organs such as the heart, kidneys and liver. Only 1% of magnesium is in the blood (also called extracellular fluid because it is outside of the cells).

Functions in the body

With such a large amount found in bones, the most important role of magnesium in the body is in bone maintenance. However, it is also involved in more than 300 reactions in the body. These reactions include:

  • Stabilizing ATP (which is the body’s energy source);
  • Turning glucose and fatty acids into energy (i.e., ATP);
  • Creation of body proteins, cholesterol, DNA and RNA;
  • Muscle contractions including heart muscles and smooth muscles… which includes blood vessels, the intestines, the bladder, and the uterus;
  • Prevention of blood clot formation; and
  • Mediation of several hormones, including secretion of parathyroid hormone and activation of vitamin D (which is technically a hormone in its active form).

Symptoms of deficiency

Because of magnesium’s involvement in muscle control, anyone who experiences general tightness, muscle cramps and muscle aches may be deficient. This also applies to those who have constipation since magnesium helps the muscles of the intestines contract and relax. Additional symptoms associated with the muscles include weakness, numbness and tingling.

Less common symptoms include anxiety, stress, insomnia, headaches, loss of appetite, nausea, vomiting, fatigue, seizures and personality changes as a result of low blood levels of calcium or potassium.

More severe symptoms of magnesium deficiency include type 2 diabetes (due to its involvement with glucose metabolism), fibromyalgia, restless leg syndrome, migraines, osteoporosis, periodontal disease, heart failure, high blood pressure (including preeclampsia), hyperlipidemia and IBS.

Causes of deficiency

Even though the kidneys will usually prevent the excretion of magnesium if intake is limited, there are still some people who are at risk for deficiency.

Of course, people who have absorption issues (such as Crohn’s disease, celiac disease or pancreatic insufficiency) are at risk for deficiency of many nutrients, including magnesium.

Those who consume an unbalanced diet or diets with large amounts of processed foods may be deficient, especially those who consume large amounts of caffeine, sugar and/or alcohol. Also, because the absorption of magnesium competes with absorption of other micronutrients, people who supplement with large amounts of calcium or vitamin B6 are also at risk.

Finally, kidney dysfunction (i.e., those that excrete too much) can cause magnesium deficiency.

Causes of and symptoms of toxicity

Excessive intake is not likely to cause toxicity because the kidneys can get rid of any magnesium that is not needed. However, people with kidney issues that prevent excretion are at risk for toxicity. As well, people who supplement with large amounts (> 600 mg/day) for an extended period of time may be at risk for toxicity.

Symptoms of toxicity include diarrhea, nausea, flushing, double vision and slurred speech. Severe toxicity can result in depression, paralysis, and cardiac or respiratory failure.

Measuring levels

Unfortunately, measuring magnesium levels is not easy because most of it is in the bones and muscles. As well, the body tends to regulate the amount of minerals in the blood, at the detriment of those same minerals inside cells. So, measuring magnesium in the blood will only tell you if there is a really bad problem.

Measuring the magnesium inside red blood cells is better than in the blood because it reflects the longer term magnesium status and will tell you sooner if there is insufficiency.

Sources of Magnesium

  • Nuts and seeds (especially cashews and pumpkin, sesame and sunflower seeds)
  • Legumes,
  • Whole grains (especially quinoa, oats, barley and brown rice),
  • Leafy green vegetables (because chlorophyll contains magnesium),
  • Seafood (especially halibut),
  • Blackstrap  molasses,
  • Corn,
  • Peas,
  • Chocolate, coffee, tea, cocoa (a little bit, but it shouldn’t be your primary source)


— Allen S. Assessing Traditional Labs from a Functional Medicine Perspective Part 2: CMC and other Important Analytes. Lecture slides.
— Allen S. Dietary Supplements. Lecture slides.
— Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth Cengage Learning; 2013.
— Linus Pauling Institute. Magnesium. In Micronutrient Information Center. Accessed on April 14, 2015.
— The World’s Healthiest Foods. Magnesium. Accessed on April 14, 2015.

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