Magnesium: Reference and Dietary Sources

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Abstract

In this article, we describe:

  • the major purposes of this specific nutrient in the human body, 
  • its experimentally confirmed health uses, 
  • conventional ways to estimate nutrient status,
  • nutrient’s toxicities and deficiencies,
  • experimentally confirmed and approved levels of the nutrient intake for different demographics,
  • dietary sources of the nutrient.

Introduction

Magnesium, an abundant mineral in the body, is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. Magnesium is required for energy production, oxidative phosphorylation, and glycolysis. It contributes to the structural development of bone and is required for the synthesis of DNA, RNA, and the antioxidant glutathione. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm.

An adult body contains approximately 25 g magnesium, with 50% to 60% present in the bones and most of the rest in soft tissues. Less than 1% of total magnesium is in blood serum, and these levels are kept under tight control. Normal serum magnesium concentrations range between 0.75 and 0.95 millimoles (mmol)/L. Hypomagnesemia is defined as a serum magnesium level less than 0.75 mmol/L. Magnesium homeostasis is largely controlled by the kidney, which typically excretes about 120 mg magnesium into the urine each day. Urinary excretion is reduced when magnesium status is low.

Assessing magnesium status is difficult because most magnesium is inside cells or in bone. The most commonly used and readily available method for assessing magnesium status is measurement of serum magnesium concentration, even though serum levels have little correlation with total body magnesium levels or concentrations in specific tissues. Other methods for assessing magnesium status include measuring magnesium concentrations in erythrocytes, saliva, and urine; measuring ionized magnesium concentrations in blood, plasma, or serum; and conducting a magnesium-loading (or “tolerance”) test. No single method is considered satisfactory. Some experts consider the tolerance test (in which urinary magnesium is measured after parenteral infusion of a dose of magnesium) to be the best method to assess magnesium status in adults. To comprehensively evaluate magnesium status, both laboratory tests and a clinical assessment might be required.

Symptomatic magnesium deficiency due to low dietary intake in otherwise-healthy people is uncommon because the kidneys limit urinary excretion of this mineral. However, habitually low intakes or excessive losses of magnesium due to certain health conditions, chronic alcoholism, and/or the use of certain medications can lead to magnesium deficiency.

Magnesium inadequacy can occur when intakes fall below the RDA but are above the amount required to prevent overt deficiency. The following groups are more likely than others to be at risk of magnesium inadequacy because they typically consume insufficient amounts or they have medical conditions (or take medications) that reduce magnesium absorption from the gut or increase losses from the body: people with gastrointestinal diseases; people with type 2 diabetes; people with alcohol dependence; older adults.

Habitually low intakes of magnesium induce changes in biochemical pathways that can increase the risk of illness over time. Magnesium may be involved in hypertension and cardiovascular disease, type 2 diabetes, osteoporosis, and migraine headaches where higher magnesium intakes might reduce the risk or severity of the condition.

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Too much magnesium from food does not pose a health risk in healthy individuals because the kidneys eliminate excess amounts in the urine. However, high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping. Forms of magnesium most commonly reported to cause diarrhea include magnesium carbonate, chloride, gluconate, and oxide. The diarrhea and laxative effects of magnesium salts are due to the osmotic activity of unabsorbed salts in the intestine and colon and the stimulation of gastric motility.

Very large doses of magnesium-containing laxatives and antacids (typically providing more than 5,000 mg/day magnesium) have been associated with magnesium toxicity, including fatal hypermagnesemia. The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost.

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Recommended Dietary Allowances (RDAs) for Magnesium

AgeMaleFemalePregnancyLactation
Birth to 6 months30 mg*30 mg*
7–12 months75 mg*75 mg*
1–3 years80 mg80 mg
4–8 years130 mg130 mg
9–13 years240 mg240 mg
14–18 years410 mg360 mg400 mg360 mg
19–30 years400 mg310 mg350 mg310 mg
31–50 years420 mg320 mg360 mg320 mg
51+ years420 mg320 mg

*Adequate Intake (AI)

Dietary Sources of Magnesium

Magnesium is widely distributed in plant and animal foods and in beverages. Green leafy vegetables, such as spinach, legumes, nuts, seeds, and whole grains, are good sources. In general, foods containing dietary fiber provide magnesium. Magnesium is also added to some breakfast cereals and other fortified foods. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially.

Tap, mineral, and bottled waters can also be sources of magnesium, but the amount of magnesium in water varies by source and brand (ranging from 1 mg/L to more than 120 mg/L).

Approximately 30% to 40% of the dietary magnesium consumed is typically absorbed by the body.

Selected Food Sources of Magnesium

FoodMilligrams
(mg) per
serving
Percent
DV*
Dry roasted almonds, 1 ounce8019
Boiled spinach, ½ cup7819
Dry roasted cashews, 1 ounce7418
Oil roasted peanuts, ¼ cup6315
Shredded wheat cereal, 2 large biscuits6115
Soymilk, 1 cup6115
Black beans, cooked, ½ cup6014
Cooked edamame, ½ cup5012
Smooth peanut butter, 2 tablespoons4912
Whole wheat bread, 2 slices4611
Avocado, cubed, 1 cup4411
Potato, baked with skin, 3.5 ounces4310
Brown rice, ½ cup4210
Plain yogurt, 8 ounces4210
Breakfast cereals, fortified with 10% of the DV for magnesium4210
Dark chocolate, 1 ounce 4110
Instant oatmeal, 1 packet369
Canned kidney beans, ½ cup358
Banana, 1 medium328
Cooked Atlantic salmon, farmed, 3 ounces266
Milk, 1 cup24–276
Halibut, 3 ounces246
Raisins, ½ cup235
Roasted chicken breast, 3 ounces226
Pan broiled ground beef, 3 ounces205
Broccoli, chopped and cooked, ½ cup123
White rice, ½ cup103
Apple, 1 medium92
Raw carrot, 1 medium72
  • *DV = Daily Value.
  • The DV for magnesium used for the values in the table above is 420 mg for adults and children age 4 years and older.
  • Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

References

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