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The truth behind magnesium oxide


Magnesium oxide is one of the most commonly used forms of magnesium in supplements, however, there are still many that consider it to be a ‘lesser’ form of magnesium compared to others. In this review we will establish the benefits of using magnesium oxide.

It's estimated that a staggering 60-80% of people don't get enough magnesium in their diets. Magnesium oxide is an excellent choice for boosting your intake, offering a host of benefits such as better sleep, enhanced relaxation, and improved cardiovascular and brain health. By ensuring your body gets the magnesium it needs, you can unlock these powerful health advantages.

However, despite these health benefits, one thing is clear, magnesium oxide is not as bioavailable as other supplemental forms of magnesium. What we do know, through extensive research magnesium oxide is an effective form of magnesium that can ultimately improve magnesium status. It also offers a very reasonably priced form alongside all the other forms of magnesium.

Assessing bioavailability – the race to better absorption

The bioavailability of supplements is a big selling point as the more bioavailable something is, the more superior it is considered. What is actually true is that higher bioavailability is NOT always better!

While some forms of magnesium supplements have higher bioavailability, the difference in overall absorption between various forms may not be significant enough to impact health outcomes in most cases. The body has mechanisms to regulate magnesium absorption based on its needs. If you require more, you absorb more, if you need less you absorb less[1].

A highly bioavailable magnesium supplement is quickly absorbed from the small intestine into the bloodstream, leading to a rapid rise in blood magnesium levels. However, when these levels surpass a critical threshold, the excess magnesium is quickly excreted by the kidneys, resulting in a shorter duration of magnesium availability to tissues. Magnesium with superior water solubility, bioavailability, and absorption rates are also quickly eliminated through the urine[2].

Magnesium absorption primarily occurs in the lower parts of the small intestine, although it can also take place throughout the entire intestinal tract via a passive transcellular process, as magnesium lacks specialised carriers to allow entry into the bloodstream. The amount of magnesium absorbed depends largely on the quantity present in the digestive tract[3].

Due to its higher elemental magnesium content and lower solubility, magnesium oxide is absorbed more slowly as it navigates the digestive tract. Consequently, it does not cause excessive elevation of blood levels and is not rapidly excreted[4].

How do get the maximum benefit from magnesium supplements

Just as in food, not all magnesium consumed is absorbed by the body with around 30-40% being typically absorbed[5]. Another factor involved in the absorption of magnesium is the presence of stomach acid which helps magnesium free from its partner compound and become its active state (ionized). So, the thing we need to consider before we start taking magnesium supplements is to consume it with food and to be aware of any medications that could impair its absorption like proton pump inhibitors.

Magnesium oxide has the greatest elemental amount of magnesium (60%) compared to magnesium citrate (15%), which means that even with lower absorption, magnesium oxide is still able to deliver more magnesium per capsule than any other form. In other words, you have a whole lot more potential of magnesium in a smaller dose.

What the research shows

When we look at research, the most common form of magnesium measurement in studies is through assessing serum (blood) magnesium levels. Serum magnesium levels are often used as a marker to determine the concentration of magnesium circulating in the bloodstream, however, serum magnesium measurements, while easy, accessible, and inexpensive, may sometimes be inadequate as they only account for less than 0.3% of total body magnesium.
This is the easiest way, however, and other methods, such as 24-hour urine excretion or the fractional excretion of magnesium (helps highlight magnesium wastage from the kidneys as well as from inadequate intake or poor absorption) and intracellular measurements via x-ray dispersion are more complicated, costly and time consuming[6].

Study 1:

To truly understand magnesium status, intracellular magnesium is the greatest measurement as it shows that magnesium has reached where it can be most utilised. In one study the researchers evaluated the effects of oral magnesium citrate and magnesium oxide supplements on intracellular magnesium levels and platelet function in healthy individuals via x-ray dispersion analysis. In a randomized, double-blind crossover trial involving 41 participants, magnesium oxide increased intracellular magnesium levels significantly more than magnesium citrate. Both supplements reduced cholesterol levels and inhibited platelet aggregation, indicating potential cardiovascular benefits. The concluding remarks were that magnesium oxide showed superior improvement in intracellular magnesium levels and cholesterol reduction compared to magnesium citrate[7].

The purpose of using magnesium is to elevate systematic levels and improve the ratio of calcium to magnesium. This is why for certain individuals, taking a higher amount of elemental magnesium in a smaller dose may be more efficient.

Study 2:

In a double-blind randomized clinical trial involving 46 elderly subjects, magnesium oxide supplementation was found to significantly alleviate insomnia symptoms and improve objective measures of sleep quality. Participants received either 500 mg of magnesium oxide or a placebo daily for 8 weeks. Compared to the placebo group, those receiving magnesium showed statistically significant increases in sleep time and efficiency, along with reductions in sleep onset latency and serum cortisol concentration. Additionally, magnesium oxide supplementation resulted in higher concentrations of serum renin and melatonin. Subjective measures, such as the Insomnia Severity Index (ISI) score, also showed significant improvement with magnesium oxide supplementation. These findings suggest that magnesium oxide supplementation may effectively alleviate insomnia symptoms and improve sleep quality in elderly individuals, addressing both subjective and objective measures of sleep disturbance[8].

Study 3:

Finally, magnesium has been known to help alleviate migraines. One study compares the efficacy of magnesium oxide and valproate sodium in preventing migraine headaches. Conducted as a single-centre, randomized, controlled, crossover trial, it lasted 24 weeks with a double-blind, 2-sequence, 2-period, 2-treatment design. Seventy patients were initially randomized, with 63 included in the analysis after seven dropouts. Patients received either magnesium oxide (500 mg) or valproate sodium (400 mg) daily for 8 weeks. The primary efficacy measures were reductions in migraine attacks, days with moderate or severe headaches, and headache duration per month compared to baseline. Results showed that magnesium oxide was as effective as valproate sodium in migraine prophylaxis, with no significant adverse effects noted[9]. Top of Form


Magnesium oxide remains a valuable addition to supplement regimes due to its efficacy and potential benefits. Despite its lower bioavailability compared to other magnesium forms, such as magnesium citrate, magnesium oxide offers higher elemental magnesium content. This higher concentration allows for slower absorption, reducing the likelihood of excess magnesium levels in the bloodstream and subsequent rapid excretion. Additionally, magnesium oxide's slower absorption rate may provide sustained benefits, making it suitable for long-term use. Therefore, we can conclude that magnesium oxide can still deliver considerable benefits and should be considered as part of a comprehensive supplement regimen.’

Author: Phil Beard, BSc (Hons), MSc, is a Nutritionist, Speaker and Trainer at Viridian Nutrition. He holds a Master’s degree in Nutrition and Health




[1] Fiorentini, D., Cappadone, C., Farruggia, G., & Prata, C. (2021). Magnesium: Biochemistry, Nutrition, Detection, and Social Impact of Diseases Linked to Its Deficiency. Nutrients, 13(4), 1136.

[2] Blancquaert L, Vervaet C, Derave W. Predicting and Testing Bioavailability of Magnesium Supplements. Nutrients. 2019 Jul 20;11(7):1663. doi: 10.3390/nu11071663. PMID: 31330811; PMCID: PMC6683096.


[3] Musso CG. Magnesium metabolism in health and disease. Int Urol Nephrol. 2009;41(2):357-62. doi: 10.1007/s11255-009-9548-7. Epub 2009 Mar 10. PMID: 19274487

[4] Ranade VV, Somberg JC. Bioavailability and pharmacokinetics of magnesium after administration of magnesium salts to humans. Am J Ther. 2001 Sep-Oct;8(5):345-57. PMID: 11550076

[5] Fine KD, Santa Ana CA, Porter JL, Fordtran JS. Intestinal absorption of magnesium from food and supplements. J Clin Invest 1991;88:396-402.

[6] Al Alawi, A. M., Majoni, S. W., & Falhammar, H. (2018). Magnesium and Human Health: Perspectives and Research Directions. International journal of endocrinology2018, 9041694.

[7] Shechter M, Saad T, Shechter A, Koren-Morag N, Silver BB, Matetzky S. Comparison of magnesium status using X-ray dispersion analysis following magnesium oxide and magnesium citrate treatment of healthy subjects. Magnes Res. 2012 Mar 1;25(1):28-39. doi: 10.1684/mrh.2012.0305. PMID: 22433473.

[8] Abbasi B, Kimiagar M, Sadeghniiat K, Shirazi MM, Hedayati M, Rashidkhani B. The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. J Res Med Sci. 2012 Dec;17(12):1161-9. PMID: 23853635; PMCID: PMC3703169.


[9] Karimi N, Razian A, Heidari M. The efficacy of magnesium oxide and sodium valproate in prevention of migraine headache: a randomized, controlled, double-blind, crossover study. Acta Neurol Belg. 2021 Feb;121(1):167-173. doi: 10.1007/s13760-019-01101-x. Epub 2019 Feb 23. PMID: 30798472.


 The information contained in this article is not intended to treat, diagnose or replace the advice of a health practitioner. Please consult a qualified health practitioner if you have a pre-existing health condition or are currently taking medication. Food supplements should not be used as a substitute for a varied and balanced diet.

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