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Magnesium is involved in a number of bodily reactions (more than 300), contributes to bone health, and helps maintain the intracellular concentration of potassium and calcium. It is also helps produce energy, as well as develop and maintain bones and other calcified tissues. Magnesium plays a role in the body’s natural defense systems against all kinds of stressors. 

Roles

What does magnesium do? 

  • Solidifies bones and teeth;
  • Maintains heartbeat;
  • Allows muscles to contract;
  • Is involved in the many reactions involving carbohydrates (sugars), lipids (fats), and proteins.

Needs

The amount of magnesium in the body is regulated primarily by the kidneys, where it is filtered and then reabsorbed. Nearly 50 to 60% of the magnesium in the body is stored in the bones, while excess intake is quickly excreted through the urine. 

Recommended Dietary Allowances (RDA) for Magnesium
Age
mg/day
Children
1 to 3 years
80
3 to 8 years
130
Preteens
9 to 13 years
240
Teenage boys
14 to 18 years
410
Teenage girls
14 to 18 years
360
Adults (men)
19 to 30 years
400
31 and up
420
Adults (women)
19 to 30 years
310
31 and up
320
Pregnant women
 
350 to 400
Nursing women
under 31
310 to 360
31 and up
420

Source: Institute of Medicine, Food and Nutrition Board, Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride, 1997.

This data reflects a consensus between Canadian and U.S. authorities, who conducted a process to standardize the recommended dietary allowances (RDAs).

NOTE: calcium inhibits magnesium absorption. These two minerals compete at the intestinal absorption site. The body needs both minerals and is able to absorb each one in adequate quantities. In the bones, however, magnesium helps bind calcium to the bones’ mineral structure. A mineral complex that contains calcium and magnesium combined with vitamin D is much more effective at fighting osteoporosis than calcium alone.

Sources

Magnesium-rich foods include green leafy vegetables, whole grain cereals, and nuts. Meats, starchy foods, and milk are relatively high in magnesium, while refined foods typically have the least amount. 

Food Sources for Magnesium: 

Food
Serving
Magnesium
Soy beans, dry roasted
250ml (1 cup)
414mg
Baking chocolate, bittersweet or semisweet
125ml (1/2 cup)
103-228mg
Black, white, and lima beans, cooked
250ml (1 cup)
127-191mg
Brazil nuts, dehydrated
60ml (1/4 cup)
133mg
Breakfast cereals, 100% bran (e.g., All Bran)
30g
111mg
Almonds, dry or oil-roasted
60ml (1/4 cup)
99-109mg
Atlantic halibut, baked
100g (3.5oz)
107mg
Cashews, dry or oil-roasted
60ml (1/4 cup)
90mg
Pine nuts, dehydrated
60ml (1/4 cup)
86mg
Atlantic pollock, baked
100g (3.5oz)
86mg
Mixed nuts, including peanuts, roasted
60ml (1/4 cup)
85mg
Spinach, boiled
125ml (1/2 cup)
83mg
Artichoke, boiled
1 medium (125g)
72mg
Tuna (bluefin or yellowfin), baked
100g (3.5oz)
64-69mg
Soy beverage, enriched
250ml (1 cup)
65mg
Wheat germ, raw
30g (1oz)
64mg
Potato with peel, baked
1 medium
55mg
Beet leaves, boiled
125ml (1/2 cup)
52mg
Haddock, baked
100g (3.5oz)
50mg
Okra (gombo), cooked
125ml (1/2 cup)
30-47mg

Source: Health Canada, Canadian Nutrient File Compilation, versions 2001b and 2005 and the United States Department of Agriculture (USDA), National Nutrient Database for Standard Reference.

Deficiency

Food-related magnesium deficiency is rare. However it may occur in individuals who: 

  • Have problems absorbing nutrients intestinally due to Crohn’s disease, celiac disease, or intestinal surgery;
  • Take certain medications such as antibiotics or immunosuppressants;
  • Take diuretics for an extended period;
  • Vomit repeatedly;
  • Suffer from kidney disease;
  • Suffer from hyperthyroidism;
  • Suffer from liver cirrhosis;
  • Suffer from alcoholism;
  • Take oral contraceptives, estrogen, or cisplatine (cancer drug).

NOTE: the elderly and blacks are more likely to suffer from a lack of magnesium due to a less varied, low-magnesium diet. 

Signs of magnesium deficiency: 

  • Confusion;
  • Disorientation;
  • Trouble speaking;
  • Anemia;
  • Weakness;
  • Loss of appetite;
  • Depression;
  • Onset of cramps, tingling, and numbness;
  • Abnormal heartbeat and heart spasms.

Indications

Beneficial properties attributable to magnesium are: 

  • Prevention of some cardiovascular disorders (probable);
  • Prevention of Type 2 diabetes complications (possible)
  • Relief from premenstrual syndrome symptoms (possible);
  • Relief from migraine symptoms (uncertain);
  • Prevention of osteoporosis (uncertain);
  • Relief from leg cramps from being overweight (uncertain);
  • Treatment of attention deficit disorder (ADD) (uncertain);
  • Improvement of athletic performance (uncertain);
  • Prevention of asthma attacks (possibly ineffective);
  • Le soulagement de la constipation occasionnelle (certain).

NOTE: 

  • Supplements should be taken with a meal to decrease the risk of diarrhea. Magnesium chloride, magnesium citrate, and magnesium gluconate are more easily absorbed and therefore cause less diarrhea;
  • Combining calcium, magnesium, and vitamin D fights osteoporosis more effectively than calcium alone since magnesium helps bind calcium to the bones.

Adverse effects

Excess magnesium from food doesn’t cause any adverse reactions. However if the magnesium comes from sources other than food, some side effects may occur. 

Signs of excess magnesium (from non-food sources): 


  • Nausea;
  • Abdominal cramps;
  • Diarrhea.

More serious side effects may occur if very high doses are ingested. These effects include metabolic alkalosis (increase in blood pH), hypokalemia (decrease in blood potassium levels), and adynamic ileus (intestinal blockage due to temporary paralysis of the small intestine). 

Cons-indications

  • Serious kidney diseases.

Interactions

Natural health products and vitamin supplements: 

  • Minerals work closely together: an excess of one may lead to a deficiency of another. For example, excess manganese or potassium taken in supplement form may lead to magnesium deficiency;
  • In women boron supplements may decrease the elimination of magnesium;
  • Calcium supplements decrease magnesium absorption but have no effect on magnesium reserves or blood levels.

Medications that may lead to magnesium deficiency: 

  • Taking long term medications that increase magnesium loss through the urine: some diuretics, antibiotics, and immunosuppressants;
  • Oral contraceptives;
  • Estrogens;
  • Some cancer drugs.

Medications that may lead to excess magnesium: 

  • Lithium;
  • Various antacids1;
  • Amiloride (diuretic) significantly increases the concentration of magnesium in the body.

Others: 

  • Taking magnesium supplements decreases the absorption of tetracycline antibiotics, nitrofurantoin, as well as certain medications used to prevent osteoporosis.1

Additional information

1Take two hours apart. 

Speak with your pharmacist if you plan to take magnesium supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take.

Other names

Magnesium, Magnesium carbonate, Magnesium chloride, Magnesium oxide, Magnesium hydroxide, Magnesium pidolate, Magnesium sulfate, Mg, Mag