Magnesium is a mineral found abundantly in foods such as pumpkin seeds, brown rice and dark chocolate, and also in dietary supplements ^[1]. The body needs magnesium for a vast array of biochemical reactions that support muscle and nervous system health, as well as cardiovascular and bone health ^[2]. 

There are different types of magnesium supplements available, which contain various forms of magnesium, such as magnesium citrate, magnesium glycinate and magnesium oxide. These different forms vary in their bioavailability (the extent to which it is absorbed in the digestive tract) and may perform different functions in the body. 

What does magnesium do?

Magnesium plays a role in over 300 of the body’s enzymatic biochemical reactions (chemical reactions that take place inside cells and form the basis of all the body’s processes), such as those involved in energy production, muscle and nerve transmission, bone mineralisation, blood glucose control and blood pressure regulation ^[2]. 

However, many people are at risk of suboptimal or chronic magnesium deficiency as a result of factors such as certain medications, excess consumption of ultra processed foods, and a general decline in the magnesium content of our food crops ^[3]. When dietary intake is inadequate or compromised, magnesium supplements may help to safeguard against magnesium deficiency and help maintain optimal health. 

Do different types of magnesium do different things?

Some studies suggest that certain forms of magnesium can target certain parts of the body, producing specific health outcomes. However, most of this research has been conducted in animals, making it difficult to translate the results to humans. 

Generally, most supplement forms of magnesium act similarly in that they help to increase magnesium levels in the body. This supports the body to carry out a variety of activities, such as those involved in energy production, protein synthesis and nerve impulse conduction, muscle contraction to support muscle and nervous system, and cardiovascular and bone health ^[4]. 

Importantly, not all forms of magnesium are created equal. Generally, organic forms of magnesium (containing carbon) tend to be more easily absorbed and therefore more bioavailable than inorganic forms ^[5].

Magnesium citrate

Magnesium citrate, an organic form of magnesium commonly found in supplements, contains magnesium attached to citric acid. Citric acid is an organic compound that is abundant in citrus fruits.

Magnesium citrate benefits

Of all the forms of magnesium studied, magnesium citrate seems to be the more easily absorbed and therefore offers the best bioavailability profile (meaning more is absorbed and reaches the circulation, so it can be utilised by the body) ^[6].

Magnesium oxide

Magnesium oxide is an inorganic form of magnesium that is relatively cheap and contains a high amount of elemental magnesium, making it a popular choice for use in supplements ^[7]. However, magnesium oxide is often poorly absorbed, which means it has limited bioavailability, and can cause gastric irritation and diarrhea, especially when taken in excess ^[8].

Magnesium oxide benefits

Like any form of magnesium, magnesium oxide can help to increase magnesium levels in the body and can also be used to treat constipation due to its laxative effect ^[9]. 

Which type of magnesium is best?

The best types of magnesium are those with higher bioavailability, such as magnesium citrate.

Which magnesium is best for sleep and anxiety?

There is some evidence to suggest that magnesium may have a beneficial effect on sleep, particularly in older adults ^[10] and may improve subjective anxiety and stress in vulnerable populations ^[11]. 

Magnesium glycinate (magnesium bound to the amino acid, glycine) has been suggested to help with sleep, however most of this evidence is based on studies regarding glycine’s role in improving sleep quality ^[12].

How do I choose a magnesium supplement?

It’s generally recommended to choose a magnesium supplement that contains forms of magnesium that are the most clinically studied and bioavailable, such as magnesium citrate. Steering clear of magnesium supplements with excessive amounts of magnesium oxide is also advisable, due to its potential to impact the stomach. Lastly, newer forms of magnesium are emerging that utilise novel technologies and show promise in overcoming potential absorption issues, so watch this space. 

References: 

1. Harvard School of Public Health. The Nutrition Source: Magnesium. https://www.hsph.harvard.edu/nutritionsource/magnesium/ [accessed 20/07/2023]
2. National Institutes of Health, US Department of Health and Human Services. Magnesium. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/ [accessed 20/07/2023]
3. DiNicolantonio, J. J., O'Keefe, J. H., & Wilson, W. (2018). Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open heart, 5(1), e000668. https://doi.org/10.1136/openhrt-2017-000668 
4. Al Alawi, A. M., Majoni, S. W., & Falhammar, H. (2018). Magnesium and Human Health: Perspectives and Research Directions. International journal of endocrinology, 2018, 9041694. https://doi.org/10.1155/2018/9041694
5. Pardo, M. R., Garicano Vilar, E., San Mauro Martín, I., & Camina Martín, M. A. (2021). Bioavailability of magnesium food supplements: A systematic review. Nutrition (Burbank, Los Angeles County, Calif.), 89, 111294. https://doi.org/10.1016/j.nut.2021.111294
6. Walker, A. F., Marakis, G., Christie, S., & Byng, M. (2003). Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium research, 16(3), 183–191.
7. Blancquaert, L., Vervaet, C., & Derave, W. (2019). Predicting and Testing Bioavailability of Magnesium Supplements. Nutrients, 11(7), 1663. https://doi.org/10.3390/nu11071663
8. Medscape. Magnesium Oxide (OTC). https://reference.medscape.com/drug/mag-ox-400-uro-mag-magnesium-oxide-999517#4 [accessed 21/07/2023]
9. Mori H, Tack J, Suzuki H. Magnesium Oxide in Constipation. Nutrients. 2021 Jan 28;13(2):421. doi: 10.3390/nu13020421. PMID: 33525523; PMCID: PMC7911806.
10. 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.
11. Boyle NB, Lawton C, Dye L. The Effects of Magnesium Supplementation on Subjective Anxiety and Stress-A Systematic Review. Nutrients. 2017 Apr 26;9(5):429. doi: 10.3390/nu9050429. PMID: 28445426; PMCID: PMC5452159.
12. Yamadera, W., Inagawa, K., Chiba, S. et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol. Rhythms 5, 126–131 (2007). https://doi.org/10.1111/j.1479-8425.2007.00262.x