Magnesium – Benefits, Sources, Dosage, Foods


The magnesium is a essential mineral to the proper functioning of the human organism. It takes part in more than 300 metabolic reactions in the body. It works in close association with sodium, potassium and calcium, with which it must remain in balance in the body. About half of the body’s magnesium is found in bones and teeth, while the rest is located in muscles, liver, and other soft tissues. It is eliminated by the kidneys.

Magnesium contributes in particular to nerve transmission and muscle relaxation after contraction, which is vital for heart function. It is essential for maintaining a regular heart rhythm, lipid metabolism, as well as regulating blood sugar and blood pressure. By its relaxing action on smooth muscles, dilating on vessels and normalizing on nerve conduction, magnesium can notably play a role in pain relief associated with PMS, menstruation and migraines, for example (see the Research section).

Food sources of magnesium

Legumes, seeds, nuts, whole grains, wheat germ, dark green leafy vegetables and brewer’s yeast are good sources of magnesium. Note that refining, especially that of cereals, as well as food processing greatly reduce their content of this precious mineral.

Food Portions Magnesium
Dry Roasted Soy Beans 250 ml (1 cup) 414 mg
Baking chocolate, semi-sweet or semi-bitter 125 ml (1/2 cup) 103-228 mg
Black or white beans, lima beans, cooked 250 ml (1 cup) 127-191 mg
Dehydrated Brazil nuts 60 ml (1/4 cup) 133 mg
Breakfast cereals, 100% bran (All bran type) 30g 111 mg
Almonds roasted in oil or dry 60 ml (1/4 cup) 99-109 mg
Baked Atlantic Halibut 100 g (3 ½ oz) 107 mg
Cashew nuts roasted dry or in oil 60 ml (1/4 cup) 90 mg
Dehydrated pine nuts (pine nuts) 60 ml (1/4 cup) 86 mg
Baked Atlantic Pollock 100 g (3 ½ oz) 86 mg
Mixed nuts, including peanuts, roasted 60 ml (1/4 cup) 85 mg
Boiled spinach 125 ml (1/2 cup) 83 mg
Boiled artichokes 1 medium (125 g) 72 mg

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

Magnesium deficiency

European and North American data indicate that dietary magnesium intake are often below the recommended nutritional intake. In North America, people with dark skin and the elderly have the lowest magnesium diet.

In general, the magnesium deficiency is difficult to diagnose because it does not cause obvious symptoms, and the amount of magnesium in the body is difficult to measure, even with a blood test. However, experts are concerned about the consequences of insufficient magnesium reserves in the body (see the Research section).

In addition to insufficient food intake, other causes can lead to magnesium deficiency:

  • Long-term use of certain medications which increase magnesium losses in the urine: loop diuretics (furosemide) and thiazide diuretics (hydrochlorothiazide, for example); antibiotics (dentamicin, amphotericin) and cyclosporine (immunosuppressant).
  • Poor intestinal absorption of magnesium caused by Crohn’s disease, celiac disease, or bowel surgery, for example.
  • Alcoholism.
  • Taking oral contraceptives, estrogens and cisplatin (anticancer medicine).
  • Excessive consumption of other mineral supplements. Minerals interact with each other, and excess manganese or potassium, for example, can cause magnesium deficiency.
Calcium supplements may decrease the absorption of magnesium, but do not appear to have an effect on magnesium stores and blood levels. So far, there have been no reports of magnesium deficiency from taking calcium supplements.

The first ones symptoms Magnesium deficiency is loss of appetite, nausea, vomiting, fatigue and weakness. If the deficiency gets worse, the following symptoms may occur: numbness, muscle twitching and cramps, irregular heartbeat, and coronary spasms.

History of magnesium

The word “magnesium” comes from the name of the Greek city Magnesia, in the vicinity of which there were large deposits of magnesium carbonate. In 1810, a British chemist by the name of Sir Humphrey Davy isolated magnesium and, in 1926, a French researcher proved, by tests on laboratory animals, that it was an essential mineral.

Magnesium research

  • Cardiovascular illnesses: Epidemiological investigations have established an inversely proportional relationship between the level of magnesium in the blood (magnesemia) and the risk of suffering from cardiovascular disorders. In other words, a chronic magnesium deficiency (hypomagnesemia) would put you at greater risk for cardiovascular disease such as coronary disease, stroke and hypertension.

However, the benefits of a nutritional intake of magnesium, equal to or slightly higher than that recommended, are difficult to quantify. They are probably modest in people who do not have a magnesium deficiency.

Other studies reported that intravenous injection of magnesium would reduce the incidence of atrial fibrillation (the most common type of heart rhythm disorder), but with low efficacy. In addition, the intake of magnesium does not reduce the length of hospital stay. Finally, there is insufficient data to state that magnesium reduces the risk of stroke or not.

Clinical studies indicate that the administration of a extra cost of magnesium may improve exercise capacity of people with coronary artery disease or have an antithrombotic effect. This supplementation is also important in patients who suffer from heart failure and who are treated with diuretics, because this medication leads to a loss of magnesium.

Magnesium also contributes to the prevention of atherosclerosis, by reducing the intestinal absorption of lipids during meals and increasing the level of good cholesterol (HDL).

In people with hypertension, magnesium supplementation can lower the blood pressure. In addition, the effects of magnesium are sufficiently convincing that in North America, medical authorities recommend a food intake high in magnesium to prevent and treat hypertension, in particular by adopting the DASH (Dietary Approaches to Stop Hypertension) diet.

The author of a summary published in 2004 recommends close monitoring of the magnesium level of patients at risk of cardiovascular disease, as well as supplementation to prevent these disorders and their recurrence. Considering all the clinical data, it seems that magnesium is more beneficial in prevention as a treatment for several cardiovascular diseases. Several authors also note that, given the low cost, ease of administration and high safety of the magnesium supplement, its use should be encouraged in patients at risk of cardiovascular disease.

  • Magnesium deficiency: A lack of magnesium is common in the elderly, especially in those placed in institutions. This deficiency can be caused by a reduction in the absorption of magnesium, increased urinary loss or certain diseases (eg insulin resistance). Some authors suggest that oral intake of magnesium, in physiological doses, would make up for this deficiency.
  • Diabetes: Epidemiological studies indicate a link between low nutritional intake of magnesium and the incidence of type 2 diabetes. In addition, the decrease in the level of blood magnesium (hypomagnesemia) increases the insulin resistance, a forerunner of diabetes. Certain complications of type 2 diabetes (neuropathy, foot ulcers) are also associated with magnesium deficiency.

If magnesium appears to contribute to diabetes prevention, its usefulness in the treatment of the disease remains controversial. Nevertheless, according to a recent meta-analysis, magnesium supplements would reduce the blood sugar of type 2 diabetics and increase the level of HDL (good cholesterol), significantly. The divergent results, to which the clinical studies arrive, can be partly explained by the differences between the magnesium salts used, their dosage and the initial magnesium levels of the participants.

The researchers also observed a tendency to magnesium deficiency in people with type 1 diabetes and a recent study shows that hypomagnesemia in these patients causes thickening of the vessel wall, causing early atherosclerosis. Preliminary trials suggest magnesium supplementation may help type 1 diabetes increase insulin sensitivity and reduce risk of complications.

  • Premenstrual syndrome (PMS) and menstrual pain. Compared to healthy people, people with PMS have a lower magnesium / calcium ratio in the blood. Researchers believe this imbalance plays an important role in PMS, especially in mood changes that characterize it.

The results of clinical studies indicate that the magnesium may help reduce symptoms of PMS, if combined with vitamin B6. A recent review also suggests that the nature of the magnesium salt plays a role, as effects have been observed with magnesium pidolate, but not with oxide of magnesium.

In two studies published in 1989 and 1990, magnesium alleviated several symptoms of dysmenorrhea. More research is needed to confirm these results.

  • Migraine: Some studies have given conflicting results. Authors of recent reviews agree that current data are limited and more studies are needed to document the effectiveness of magnesium in relieving migraine.
  • Kidney stones (kidney stones): As magnesium increases the solubility of calcium, especially in the urine, it appears to have a preventive effect on kidney stones. It also reduces the intestinal absorption of oxalate, a substance that contributes to the formation of stones.

The use of oxide salts and magnesium hydroxide gives mixed results which would be attributable to the weak absorption of these forms of magnesium, whereas another study had reported a prophylactic effect of magnesium hydroxide. However, the potassium-magnesium-citrate mixture significantly more effective in preventing the recurrence of kidney stones.

  • Athletic performance: Exercise can reduce magnesium stores. Low stores combined with insufficient food intake can reduce physical exertion. Ten small studies have looked at the performance effectiveness of magnesium supplementation: 5 have shown positive results, 5 have shown inconclusive results.
  • Osteoporosis. Magnesium plays an important role in bone metabolism and the maintenance of density bone. Magnesium deficiency has recently been shown to cause osteoporosis in laboratory rats.

In humans, epidemiological studies have established an association between magnesium intake (food and supplements) and bone density in people with white skin. They also confirm that magnesium deficiency plays an important role in osteoporosis.

Clinical studies of the effects of supplementation are rare. Two preliminary trials conducted in the early 1990s with postmenopausal women indicate that taking a magnesium supplement could have a positive effect on the prevention and progression of osteoporosis; an effect that has been confirmed in a recent study.

  • Leg cramps during pregnancy. According to a synthesis published in 2002, magnesium supplements are the best treatment for leg cramps that sometimes occur during pregnancy. They would decrease the frequency and have no harmful effect on childbirth and postpartum. However, the benefits of magnesium would be modest; some researchers even go so far as to conclude that it has no effect. Furthermore, magnesium supplementation has no convincing effect on the night cramps of women who are not pregnant.
  • Attention deficit hyperactivity disorder(ADHD). In a study of children with ADHD, 95% of them were found to have signs of magnesium deficiency. If some clinical studies suggest that daily intake of magnesium, only or combined with vitamin B6, can improve the condition of hyperactive children, additional studies are needed to confirm the effectiveness of magnesium.
  • Asthma. In medicine, intravenous magnesium sulfate has been shown to relieve acute asthma attacks, especially in children.

Orally, however, magnesium has not been shown to be very effective in preventing asthma, either in terms of frequency of attacks or their severity. It could decrease the reactivity of the bronchi, but not all studies on the issue come to the same conclusions.

On the other hand, the combination of magnesium sulfate with conventional treatment (beta-agonist, corticosteroid), intravenously or misting, has shown some effectiveness, especially in children with severe symptoms.

  • Fibromyalgia. Two preliminary studies indicate that a magnesium and malic acid supplement could relieve the pain caused by fibromyalgia. The authors of the review looked at 3 preliminary clinical trials (33 subjects in all) of children with autism who were given magnesium and vitamin B6 supplements. They concluded that the data were clearly insufficient to judge the clinical efficacy of this supplementation.
  • Hearing loss. Oral magnesium therapy appears to reduce the incidence of hearing loss that is idiopathic or caused by noise. Other studies are necessary to confirm this preventive effect.
  • Neuroprotection. Premature delivery can cause neurological conditions such as deafness, blindness, or sensorineural deficits. Meta-analyzes reported that taking prenatal magnesium could improve the motor functions of children born prematurely. Likewise, magnesium sulfate appears to reduce the risk of developing cerebral palsy in babies at risk of being born prematurely. The optimal dosage remains to be determined.
  • Anxiety. Most studies have looked at the effects of combining magnesium with vitamins or natural products. Only one study reported an absence of the effect of magnesium on anxiety used in monotherapy.

Magnesium dosage

Cardiovascular protection

  • Consume daily food rich in magnesium, such as whole grains, nuts, seeds, legumes and dark green leafy vegetables. See the table of recommended nutritional intakes below.
  • In the presence of a risk factor (insulin resistance, metabolic syndrome, type 2 diabetes, family history of cardiovascular disease, for example), if food measures are not enough, take, with a meal, a supplement providing 300 mg of magnesium.
  • In case of hypertension, start with a dosage of 300 mg per day, with a meal. If necessary, the dosage can be increased up to 1000 mg per day, in divided doses.
In the presence of risk factors or diabetic or cardiovascular disease, follow-up by a health professional is necessary.

Premenstrual syndrome

  • Take a meal supplement with 300 mg of magnesium. If after 2 months the results are not significant, take 300 mg twice a day.
In case of supplementation, it is best to divide the doses and take them with a meal to reduce the risk of diarrhea (magnesium has a laxative effect): do not exceed 350 mg per dose. Favor the gluconate, the citrate where the magnesium chloride because these supplements are less likely to cause diarrhea and are a more digestible source of magnesium than other forms. See the section on tablets to learn more about the different magnesium salts.


Recommended nutritional intake of magnesium
Age mg / day
1 to 3 years 80
from 3 to 8 years old 130
9 to 13 years old 240
Boy, 14 to 18 years old 410
Girl, 14 to 18 years old 360
Male, 19 to 30 years old 400
Woman, 19 to 30 years old 310
Male, 31 and over 420
Female, 31 and over 320
Pregnant woman 18 and under: 400
19 to 30 years old: 350
31 and over: 360
Breastfeeding woman 18 and under: 360
19 to 30 years old: 310
31 and over: 320

Source: Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride, 1997, Institute of Medicine, Food and Nutrition Board.
These data are the result of a consensus between the Canadian and American authorities who have undertaken a process of standardization of the recommended nutritional intakes (RDA).




  • Canadian and American authorities have established the maximum tolerable intake magnesium as extra cost (table below). It’s actually the daily dosage from which magnesium supplements have caused a laxative effect in some people in a few studies. In other studies, higher dosages (up to 1,200 mg per day) did not cause diarrhea at the participants.
  • Note that magnesium provided by food does not cause diarrhea and that the laxative effect of magnesium salts easily assimilated is much less pronounced (see the section On tablets below).
  • In case of diarrhea, discontinue supplementation and resume it later, in smaller doses or in divided doses.
Maximum tolerable intake of magnesium supplement
Age mg / day
1 to 3 years 65 mg
from 4 to 8 years old 110 mg
9 to 13 years old 280 mg
13 and over 350 mg

Source: Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride, 1997, Institute of Medicine, Food and Nutrition Board, pages 246 and 245.


  • Serious kidney disease. The vast majority of reported cases of excess magnesium in the body are associated with kidney failure.

Side effects

  • At the recommended dosages, side effects are usually limited to diarrhea or intestinal irritation.


With plants or supplements

  • Boron supplements appear to decrease the elimination of magnesium in women.
  • Calcium supplements may decrease the absorption of magnesium, but do not appear to have an effect on magnesium stores and blood levels. So far, there have been no reports of magnesium deficiency from taking calcium supplements.

With medication

  • Taking magnesium supplements reduces the absorption of antibiotics of the tetracycline family. Take 2 hours apart.
  • Taking magnesium supplements may reduce the absorption of nitrofurantoin (an antibiotic). Take 2 hours apart.
  • Taking magnesium supplements can affect the absorption of biophosphonates (alendronate and etidronate), used for osteoporosis. Take 2 hours apart.
  • If you are on treatment with amiloride (a diuretic), consult your doctor before taking a magnesium supplement: this combination can cause too much magnesium in the body.
Magnesium, the forgotten nutrient

Whether in popular discourse or in the medical community, we often hear about calcium, but very little about magnesium. By the way, before reading the above, who could have named a good source of dietary magnesium? However, everyone is able to name a good source of calcium! However, scientific data shows that magnesium deficiency is more important in our society than calcium deficiency. The elderly and people with black skin are the populations with the highest risk of deficiency.

Magnesium plays multiple roles in the body. In general, we can say that, wherever calcium plays a role in the contraction, magnesium plays the reverse role to facilitate relaxation. Its presence is therefore essential for the proper functioning of muscles, arteries and even nerve cells. According to some authors, magnesium deficiency is implicated in disorders ranging from nervousness, anxiety and fatigue to arteriosclerosis, metabolic syndrome (syndrome X) and impairments of the immune system.

On the bone level, magnesium contributes to the fixation of calcium in the bone matrix (mineral structure of the bone). Thus, a mineral complex including calcium, magnesium and other trace elements, combined with vitamin D, is much more effective in fighting osteoporosis than calcium alone.

Some claim that calcium inhibits the absorption of magnesium. It is true that there is competition between these two minerals at the absorption site in the intestine. However, the body needs both minerals and is able to absorb both of them in adequate amounts.

Rate difficult to measure
To measure the iron or calcium level, a blood test is enough. However, this is not the case for magnesium since the blood level of magnesium does not reflect the state of the reserves. In fact, the level of magnesium circulating in the blood can be adequate despite very deficient reserves.

The supplement dose
In Canada and the United States, the maximum dose of supplements of magnesium is set at 350 mg per day for people over 13 years of age. However, this dose is in contradiction with the recommended nutritional intake for men (420 mg per day) and for pregnant women (from 350 mg to 400 mg), as well as with the dosages used in clinical studies. For example, in hypertension and PMS trials, up to 1,000 mg of magnesium was used daily in divided doses of 250 mg to 300 mg with meals.

In light of this information, this 350 mg dose therefore represents the maximum limit of magnesium supplement per dose (or dose) and not per day. It has been established because above 350 mg per dose, the risk of diarrhea increases.

Furthermore, the type of magnesium salt used is important: the less it is absorbed (bioavailable), the more the risk of diarrhea increases. For example, a magnesium oxide may cause more diarrhea than a citrate (see the section on tablets, below).

A very important contraindication exists for people suffering from kidney failure. For these patients, any mineral supplementation should be followed up with a healthcare professional.

  • The magnesium is marketed as salts (chloride, citrate, gluconate, hydroxide, oxide, etc.) whose elemental magnesium content varies considerably (see the table below). As is the case with all mineral supplements sold in Canada, the content is indicated in milligrams of elemental magnesium.
  • The magnesium contained in these salts is more or less assimilated by the body (bioavailability and solubility). The less the magnesium of a salt is assimilated, the less it will be used by the body and the greater the laxative effect. If we want to fill or prevent a magnesium deficiency, we will rather seek an easily assimilated salt (good bioavailability and good solubility), which will also have less laxative effects.
Salt Content
in magnesium
Bioavailability Solubility
Chloride 12% good very good
Citrate 16.2% good good
Gluconate 5.4% good average
Carbonate 40% bad nothing
Hydroxide 41.5% bad low
Oxide 60.3% bad average

Be the first to comment

Leave a Reply

Your email address will not be published.