Simply Magnesium Part 2: Bioavailability & Supplementation

Immune Health

What if you discovered a supplement that could significantly help in the prevention of heart disease, cancer, strokes, osteoporosis and dementia? A supplement that is a key player in managing energy, depression, hormonal balance, brain health, musculoskeletal function and adrenal support?

And what if that supplement wasn’t a hi-tech formula, or an obscure tropical plant extract…

…but simply magnesium.

In Nutrigold Simply Magnesium Part 1 we explored the many areas of health that required magnesium; from fundamental cellular processes of ATP production and pH balance to function of nerve cells, hormones, neurotransmitters and enzymes throughout the body. But is magnesium deficiency really that prevalent in the population? Are you getting enough of this crucial mineral on a daily basis? And if not, then what are the most efficacious and most bioavailable forms of magnesium to optimise levels of this essential mineral?

Magnesium Deficiency

There are two types of nutrient deficiencies, frank deficiencies (such as scurvy from Vitamin C deficiency or goitre from iodine deficiency) and subclinical deficiencies (a clinically silent reduction in physiological, cellular and/or biochemical functions). It is the latter that is most concerning as it is hard to diagnose and predisposes to numerous chronic diseases.

Because serum magnesium does not reflect intracellular magnesium, the latter making up more than 99% of total body magnesium, most cases of magnesium deficiency are undiagnosed. Symptoms of subclinical magnesium deficiency are varied including:

  • Poor mood – depression, anxiety, insomnia, headaches, irritability, stress
  • Low energy – chronic fatigue, physical and mental fatigue, lethargy, poor memory and concentration
  • Physical performance – low energy production, poor cardiovascular fitness, muscle cramps, muscle weakness

Furthermore, because of chronic diseases, medications, decreases in food crop magnesium contents, and the availability of refined and processed foods, most people in modern societies are at risk for magnesium deficiency.[1] For example, commonly prescribed drugs like proton-pump inhibitors (PPIs including omeprazole) can impair the gastrointestinal absorption of magnesium. This effect may be the result of a drug-induced decrease in the pH of the intestinal lumen that alters the affinity of transient receptor potential melastatin-6 and melastastin-7 (TRPM6, TRPM7) channels on the apical surface of enterocytes for magnesium.[2]

Dietary surveys of people in Europe and in the United States still reveal that intakes of magnesium are lower than the recommended amounts.[3] Epidemiological studies in Europe and North America have shown that people consuming Western-type diets are low in magnesium content, i.e. <30–50% of the Recommended Daily Allowance (RDA) for magnesium. It is suggested that the dietary intakes of magnesium in the United States have been declining over the last 100 years from about 500 mg per day to 175–225 mg per day. This is likely a result of the increasing use of fertilisers and processed foods.[4] Current magnesium Reference Nutrient Intakes (RNIs) for the UK is 400-420mg per day for men, 310-320mg per day for women and 350-360mg daily for pregnant women.

Certain individuals will need to supplement with magnesium to prevent suboptimal magnesium deficiency, especially if trying to obtain an optimal magnesium status to prevent chronic disease. Subclinical magnesium deficiency increases the risk of numerous types of cardiovascular disease, costs nations around the world an incalculable amount of healthcare costs and suffering and should be considered a public health crisis. That an easy, cost-effective strategy exists to prevent and treat subclinical magnesium deficiency should provide an urgent call to action.

Sources of Magnesium

Water accounts for ~10% of daily magnesium intake, chlorophyll (and thus green vegetables such as spinach) is the major food source of magnesium.[5] Nuts, seeds and unprocessed cereals are also rich in magnesium. Legumes, fruit, fish and meat have an intermediate magnesium concentration. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran resulting in foods such as white rice and breads, lower magnesium content substantially. Low magnesium concentrations are found in dairy products, except milk.[6] Cooking and heating of food also affects the mineral levels, including magnesium. For example, boiling vegetables and grains in water causes mineral loss into the cooking water.[7]

In addition, soil levels of magnesium have fallen, leading to reduced uptake by plants and animals through the food chain. McCance and Widdowson show a 24% drop in vegetable magnesium levels, a 16% reduction in fruit, and a 10% drop in meat, between 1940 and 1991.[8] In fact the soil loss is probably greater than these statistics suggest, as the vegetables in the 1940 study were boiled for much longer times. Broccoli, for example, was boiled for 45 minutes in the 1940 study, but for only 15 minutes in the 1991 study.

Magnesium Absorption and Bioavailability

Magnesium homeostasis is maintained by the intestine, the bone and the kidneys. Magnesium requires stomach acid to enhance solubility then is mainly absorbed via mineral transporters in the small intestine via passive gradient forces, although some is also taken up via the large intestine. Mineral competition, such as from calcium and zinc, can inhibit magnesium absorption across the transporters, as can other dietary factors such as phytates found in vegetables and plant matter and oxalates high in tea that can bind to minerals preventing their absorption in the gut.[9]

Of the total dietary magnesium consumed, only about 24%–76% is absorbed in the gut the rest is eliminated in the faeces.[10] It is worth noting that intestinal absorption is not directly proportional to magnesium intake but is dependent mainly on magnesium status. The lower the magnesium level, the more of the mineral is absorbed in the gut, thus relative magnesium absorption is high when intake is low and vice versa. The kidneys are also crucial in magnesium homeostasis as serum magnesium concentration is primarily controlled by its excretion in urine. Diuretic medication can promote magnesium deficiency due to action of fluid balance in the kidneys.

Magnesium absorption and excretion is influenced by different hormones. It has been shown that 1,25-dihydroxyvitamin D [1,25(OH)2D] can stimulate intestinal magnesium absorption. On the other hand, magnesium is a cofactor that is required for the binding of Vitamin D to its transport protein, the Vitamin D binding protein (VDBP). Moreover, conversion of Vitamin D by hepatic 25-hydroxlation and renal 1α-hydroxylation into the active, hormonal form 1,25(OH)2D is magnesium-dependent. Magnesium deficiency, which leads to reduced 1,25(OH)2D and impaired parathyroid hormone response, has been implicated in “magnesium-dependent vitamin-D-resistant rickets”. Magnesium supplementation substantially reversed the resistance to vitamin D treatment.[11]

Several other factors, such as oestrogen or parathyroid hormone (PTH), are also involved in the magnesium excretion. This means that oral contraceptives may contribute to subclinical magnesium deficiency.

Magnesium Supplementation

So now we come to the big question: how much to take, and what is the best form?

How much to take varies hugely from person to person. Factors include age, the person’s current magnesium status, diet, soil magnesium levels, the health of the small intestines and kidneys in particular, and all the other factors for absorption discussed above. In addition, pregnant and lactating women need higher levels. Many would agree that the current RNIs for magnesium fall far short of actual health requirements especially as dietary sources might contain low levels of this essential mineral. This means that supplementation may be required.

Nutrients in food supplements need to be in a form that the body can absorb and effectively use (i.e. bioavailable forms). Minerals need to be bound to a carrier (or ligand) to make sure they are in a stable state, can be absorbed and effective at the required site(s) of action around the body. The form of the carrier takes is especially important, as this can affect the mineral’s absorption and bioavailability, as well as impact on the body’s cells, tissues and systems. Organic carriers, so called because they are also found naturally in the body tissues and fluids, including citrates and gluconates, increase absorption and bioavailability of food supplement minerals compared to inorganic carriers, such as carbonates and oxides. This makes organic magnesium citrate a highly bioavailable food supplement compared to the lesser oxide forms.[12],[13] A Vitamin B6 supplement is often prescribed alongside magnesium to improve uptake by the cells.

Certain levels of calcium carbonates and magnesium oxide food supplements can induce unwanted side digestive side effects such as laxative actions and neutralising stomach acid, reducing absorption in the small intestine, not desirable side effects in any food supplement!  It’s also worth knowing that calcium carbonate is in fact chalk – a cheap way of supplementing a poorly absorbed form of calcium.  

Absorption of magnesium across the skin (transdermal) can also be used – Magnesium sulphate is the form of magnesium in Epsom salts often used in a warm bath to relax muscles.

In conclusion, subclinical magnesium deficiency can affect many areas of health and may contribute to long-term conditions such as cardiovascular disease. Oral supplementation, using a bioavailable organic citrate form, alongside diet and lifestyle can help to support magnesium levels in the body.


  1. Gröber U, Schmidt J, Kisters K. Magnesium in Prevention and Therapy. Nutrients. 2015 Sep 23;7(9):8199-226. doi: 10.3390/nu7095388. Full paper
  2. Perazella, M.A. Proton pump inhibitors and hypomagnesemia: A rare but serious complication. Kidney Int. 2013, 83, 553–556 Full paper
  3. Moshfegh, A.; Goldman, J.; Ahuja, J.; Rhodes, D.; LaComb, R. What We Eat in America, NHANES 2005–2006: Usual Nutrient Intakes from Food and Water Compared to 1997 Dietary Reference Intakes for Vitamin D, Calcium, Phosphorus, and Magnesium; U.S. Department of Agriculture, Agricultural Research Service: Washington, DC, USA, 2009.
  4. Rude, R.K. Magnesium. In Modern Nutrition in Health and Disease, 11th ed.; Ross, A.C., Caballero, B., Cousins, R.J., Tucker, K.L., Ziegler, T.R., Eds.; Lippincott Williams & Wilkins: Baltimore, MA, USA, 2012; pp. 159–175.
  5. Marx, A.; Neutra, R.R. Magnesium in drinking water and ischemic heart disease. Epidemiol. Rev. 1997, 19, 258–272 View abstract
  6. Magnesium. Available online: magnesium (accessed on 23rd march 2018).
  7. Kimura M et al (1990) Cooking losses of minerals in foods and its nutritional significance. J Nutr Sci Vitaminol (Tokyo). 36 Suppl 1:S25-32; discussion S33 View abstract
  9. Gröber U, Schmidt J, Kisters K. Magnesium in Prevention and Therapy. Nutrients. 2015 Sep 23;7(9):8199-226. doi: 10.3390/nu7095388. Full paper
  10. Jahnen-Dechent, J.; Ketteler, M. Magnesium basics. Clin. Kidney J. 2012, 5, i3–i14 Full paper
  11. Zittermann, A. Magnesium deficit? Overlooked cause of low vitamin D status? BMC Med. 2013, 11, 229 Full paper
  12. Walker et al (2003) Mg citrate found more bioavailable than other Mg preparations in a randomised, double blind study. Magnesium Res 16:3 Full paper
  13. Lindberg JS(1990) Magnesium bioavailability from magnesium citrate and magnesium oxide. J Am Coll Nutr. 1990 Feb;9(1):48-55 View abstract
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Simply Magnesium: Part 1
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Improving Cognitive Resilience, Mood & Sleep – Are B Vitamins the Answer?

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Elisabeth Philipps

Karen Devine

Karen Devine

Shelley Harvey

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