*Here is a link to the alphabetical list of Dietary Fact Sheets From the Office of Dietary Supplements. It is an excellent complete resource.
Here are the links to the various sections of the Magnesium Fact Sheet:
Table of Contents
Here are some excerpts from above:
Magnesium, an abundant mineral in the body, is naturally present in many foods, added to other food products, available as a dietary supplement, and present in some medicines (such as antacids and laxatives). Magnesium 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 [1-3]. 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 .
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 .
Table 1: Recommended Dietary Allowances (RDAs) for Magnesium  Age Male Female Pregnancy Lactation Birth to 6 months 30 mg* 30 mg* 7–12 months 75 mg* 75 mg* 1–3 years 80 mg 80 mg 4–8 years 130 mg 130 mg 9–13 years 240 mg 240 mg 14–18 years 410 mg 360 mg 400 mg 360 mg 19–30 years 400 mg 310 mg 350 mg 310 mg 31–50 years 420 mg 320 mg 360 mg 320 mg 51+ years 420 mg 320 mg
*Adequate Intake (AI)
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 [1,3]. 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 . Selected food sources of magnesium are listed in Table 2.
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 [2,9].
For to jump to Table 2: Selected Food Sources of Magnesium , click on Sources Of Magnesium
The U.S. Department of Agriculture’s (USDA’s) FoodData Central  lists the nutrient content of many foods and provides comprehensive list of foods containing magnesium arranged by nutrient content and by food name.
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.
Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures, personality changes, abnormal heart rhythms, and coronary spasms can occur [1,2]. Severe magnesium deficiency can result in hypocalcemia or hypokalemia (low serum calcium or potassium levels, respectively) because mineral homeostasis is disrupted .
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
The chronic diarrhea and fat malabsorption resulting from Crohn’s disease, gluten-sensitive enteropathy (celiac disease), and regional enteritis can lead to magnesium depletion over time . Resection or bypass of the small intestine, especially the ileum, typically leads to malabsorption and magnesium loss .
People with type 2 diabetes
Magnesium deficits and increased urinary magnesium excretion can occur in people with insulin resistance and/or type 2 diabetes [27,28]. The magnesium loss appears to be secondary to higher concentrations of glucose in the kidney that increase urine output .
People with alcohol dependence
Magnesium deficiency is common in people with chronic alcoholism . In these individuals, poor dietary intake and nutritional status; gastrointestinal problems, including vomiting, diarrhea, and steatorrhea (fatty stools) resulting from pancreatitis; renal dysfunction with excess excretion of magnesium into the urine; phosphate depletion; vitamin D deficiency; acute alcoholic ketoacidosis; and hyperaldosteronism secondary to liver disease can all contribute to decreased magnesium status [2,29].
Older adults have lower dietary intakes of magnesium than younger adults [23,30]. In addition, magnesium absorption from the gut decreases and renal magnesium excretion increases with age . Older adults are also more likely to have chronic diseases or take medications that alter magnesium status, which can increase their risk of magnesium depletion [1,32].
Habitually low intakes of magnesium induce changes in biochemical pathways that can increase the risk of illness over time. This section focuses on four diseases and disorders in which magnesium might be involved: hypertension and cardiovascular disease, type 2 diabetes, osteoporosis, and migraine headaches.
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 .
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 in a 28-month-old boy  and an elderly man . Symptoms of magnesium toxicity, which usually develop after serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, retention of urine, ileus, depression, and lethargy before progressing to muscle weakness, difficulty breathing, extreme hypotension, irregular heartbeat, and cardiac arrest . The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost [1,31].
The FNB has established ULs for magnesium that apply only to supplemental magnesium for healthy infants, children, and adults (see Table 3) .
Table 3: Tolerable Upper Intake Levels (ULs) for Supplemental Magnesium  Age Male Female Pregnant Lactating Birth to 12 months None established None established 1–3 years 65 mg 65 mg 4–8 years 110 mg 110 mg 9–18 years 350 mg 350 mg 350 mg 350 mg 19+ years 350 mg 350 mg 350 mg 350 mg
Interactions with Medications
Several types of medications have the potential to interact with magnesium supplements or affect magnesium status. A few examples are provided below. People taking these and other medications on a regular basis should discuss their magnesium intakes with their healthcare providers. [For details see the Magnesium Fact Sheet for Health Professionsls.]
Magnesium-rich supplements or medications can decrease the absorption of oral bisphosphonates, such as alendronate (Fosamax®), used to treat osteoporosis . Use of magnesium-rich supplements or medications and oral bisphosphonates should be separated by at least 2 hours .
Magnesium can form insoluble complexes with tetracyclines, such as demeclocycline (Declomycin®) and doxycycline (Vibramycin®), as well as quinolone antibiotics, such as ciprofloxacin (Cipro®) and levofloxacin (Levaquin®). These antibiotics should be taken at least 2 hours before or 4–6 hours after a magnesium-containing supplement [58,63].
Chronic treatment with loop diuretics, such as furosemide (Lasix®) and bumetanide (Bumex®), and thiazide diuretics, such as hydrochlorothiazide (Aquazide H®) and ethacrynic acid (Edecrin®), can increase the loss of magnesium in urine and lead to magnesium depletion . In contrast, potassium-sparing diuretics, such as amiloride (Midamor®) and spironolactone (Aldactone®), reduce magnesium excretion .
Proton pump inhibitors
Prescription proton pump inhibitor (PPI) drugs, such as esomeprazole magnesium (Nexium®) and lansoprazole (Prevacid®), when taken for prolonged periods (typically more than a year) can cause hypomagnesemia . In cases that FDA reviewed, magnesium supplements often raised the low serum magnesium levels caused by PPIs. However, in 25% of the cases, supplements did not raise magnesium levels and the patients had to discontinue the PPI. FDA advises healthcare professionals to consider measuring patients’ serum magnesium levels prior to initiating long-term PPI treatment and to check magnesium levels in these patients periodically .