Magnesium, Sleep, and Muscle Recovery

Not only is magnesium a micronutrient and supplement that athletes are interested in, different forms of magnesium are also promoted—often by supplement companies—as being specific to improvements in sleep, muscle health, and/or recovery. But does a specific form matter? And does additional magnesium matter in the presence of a magnesium-rich diet?

In this article, I’m going to review the following:

• How much magnesium do we need? What about its role as a laxative?

• How does magnesium move from the diet/intestine and into circulation?

• Interpreting biomarkers: serum versus red blood cell (RBC) versus urine magnesium.

• What information is consistently missing from supplemental magnesium studies?

• What role does magnesium have in sleep? Muscle recovery?

Rather than writing the word magnesium out a thousand times, I’m going to shorten it to Mg.

How Much Magnesium Do We Need?

The recommended dietary allowance (RDA) for Mg in those aged 19-30 years is 400 mg for males and 310 mg for females. (1) When a deficiency is present, side effects include muscle weakness, cramps, and fatigue. (2)

The tolerable upper intake limit (UL) for Mg is specific to supplemental forms at 350 mg, which is unique as the UL is typically well above the RDA and considers a combined dietary and supplemental intake. (1,3) This UL was set on the basis of four studies showing diarrhea in some people when provided with Mg salt doses greater than 350 mg/day. (3)

Minimizing the risk of diarrhea with supplementation includes splitting up a single dose into smaller ones throughout the day and consuming supplements with food (3) Ultimately, Mg intake from foods above the supplemental UL has not been deemed a concern. (4)

A few examples of available magnesium forms that are NSF Certified for Sport.

The Movement of Magnesium: From Diet to Bloodstream

Roughly 25-75% of the Mg consumed is absorbed into circulation. (2,5) This range depends on how much Mg is consumed in a single dose and the body’s need for Mg. (5) Thirty-percent of Mg is absorbed in the jejunum and ileum (the areas within the small intestine furthest from the stomach) via the TRPM6 transporter. Once inside the enterocyte (the single-cell wall lining the intestine), Mg is pumped out into the bloodstream. When the body senses a declining Mg value, more Mg is absorbed from the gut via these transporters. The opposite is true for Mg sufficiency, where ~30% of Mg is absorbed. (5)

Eighty-percent of Mg is absorbed passively in between the enterocytes and directly into the bloodstream. (5)

Large intakes of Mg in the realm of 550 mg drops absorption rates to 30%. Smaller doses of Mg around 40 mg increases rates up to 60-75%. (5)

There are different forms of Mg, meaning what the elemental Mg is attached to. For instance, Mg oxide, chloride, or L-threonate. Research shows that the form does not seem to matter when it comes to how much can be absorbed (a.k.a., bioavailability). (6)

Interpreting Biomarkers: Serum vs. Red Blood Cell (RBC) Magnesium

Within the body, Mg exists ~50-60% within the bones and teeth, ~39-49% within soft tissues (~25% of which is within skeletal muscles), and ~0.3-0.8% in the blood—meaning serum and red blood cell (RBC) magnesium levels represent poor proxies for total body levels. (5-7) Similar to calcium regulation, when the blood levels drop, there is a stimulus to pull calcium and Mg from its stores to normalize blood values. A within-range blood reading of Mg can be misinterpreted as dietary sufficiency. Regardless, normal serum values are considered as 0.7-1 mmol/L. (6,7)

One proposed solution is to test for RBC Mg, given its slightly higher Mg content of 0.5% Mg compared to ~0.3% of serum Mg. (7) The normal range is proposed somewhere around 4.2-6.8 mg/dL, whereas above 6.0 mg/dL has also been proposed as a minimal threshold. (6) However, this method has been challenged due to RBC studies neither measuring nor reporting comparisons to other Mg measurements (e.g., urine, muscle), nor being long enough in study design to show validity as a proxy. (7)

Urinary Mg measurements neither correlate with Mg ingestion nor total body status. The kidneys can upregulate reabsorption or promote excretion based on the body’s demand. (7)

As an example of biomarkers in practice, Liu et al. (2016) provided Mg L-threonate to older adults with cognitive impairment and sleep disorders. The dose was 25 mg/day over 12 weeks. Plasma, urine, and RBC Mg were all measured. Supplementation significantly increased urinary Mg; increased RBC Mg (p=0.829), although not significantly; and did not affect serum Mg levels. Regardless, supplementation significantly improved functioning and cognitive processing. (8)

What’s Missing from the Magnesium Supplement Literature?

What’s missing is a true comparison study across different Mg forms, in a healthy population without sleep disorders or other medical conditions, consuming the RDA for Mg, and studying a specific outcome. For instance, malate versus citrate versus L-threonate versus placebo, in a population without sleep disorders meeting 100% of the RDA for Mg through diet, and evaluating sleep quality. Maximizing dietary Mg helps researchers understand if additional supplementation makes a difference or if optimizing one's diet is enough.

I found two studies that first evaluated dietary Mg intake at baseline. Reno et al. (2022) reported dietary Mg meeting ~50% of the RDA in both the placebo and treatment groups of 22 male and female college students. The treatments group received 350 mg/day Mg glycinate over a 10-day trial. The researchers reported significant improvements in muscle soreness hours after having completed exercise designed to induce muscle damage. (9) Another study by Steward et al. (2019)* evaluated running performance in nine recreational male runners. All participants purposefully consumed a low-magnesium diet during the 4-week crossover study, while supplementing over a 7-day period with 500 mg/day Mg oxide-and-stearate before a 10-km downhill running time trial (downhill running increases muscle damage). Significant improvements were found via reduced IL-6 levels and muscle soreness. (10)

These studies show that supplemental Mg intake, compared to a placebo group of zero supplemental Mg, easily had the effect of correcting for a dietary deficiency. However, any changes or improvement may not have been the magic of above-and-beyond Mg supplementation.

*This study was behind a paywall, so my complete insight of the study is low.

Besides Bioavailability, Is There an Argument for Different Forms of Magnesium?

The only study I could find to compare different forms of Mg was one referenced by Slutsky et al. (2010) that also included results from unpublished data sets. Their work was with rats. (11) The data within this paper is often referenced by supplement companies regarding improved absorption rates—or the bioavailability—of certain magnesium forms (e.g., Mg L-threonate; a.k.a., Magtein®).

Before introducing the Slutsky et al. (2010) research, understanding Mg and the blood brain barrier (BBB) is helpful. The BBB controls what and how much of something can pass into the brain. Intravenous Mg, in the sulphate form, has been shown to increase blood levels by 100-300%, but cerebrospinal fluid (CSF) Mg levels by only 10-19%. If the goal is to increase brain levels of Mg, the form of Mg and its BBB bioavailability is important.

One of the unpublished data sets compared the absorption, retention, and excretion in rats consuming Mg chloride, Mg citrate, Mg glycinate, Mg gluconate, Mg L-threonate, and Mg gluconate+milk, finding the latter two having higher bioavailability. Additionally, the researchers evaluated Mg chloride, Mg L-threonate, Mg gluconate+milk, and a placebo. Over the course of one month, Mg was provided to rats through their drinking water. CSF was collected at baseline and then at days 12 and 24. What Slutsky et al. found was a significant increase of 7% in the CSF Mg for the L-threonate group compared to a 9% decrease in placebo rats. Percentage changes for Mg chloride and Mg gluconate+milk were not provided. (11)

Mg L-threonate significantly higher presence in the cerebrospinal fluid compared to other forms of magnesium. Slutsky et al. (2010).

When aging rats were provided with various Mg doses of 50 mg/kg/day (for a 200-lb. human, this could equate to 4.5 grams per day), Mg L-threonate showed a significant improvement in short- and long-term memory when compared with Mg chloride, Mg citrate, and Mg gluconate+milk. All Mg forms resulted in improvements. (11)

A side note, but of interest for Mg supplements: Many products also include vitamins D and B6. The former improves Mg absorption and the latter, when deficient, reduces Mg absorption and increases its excretion. (5,12) The presence of protein and carbohydrates also optimize Mg absorption, so if taking Mg at night for sleep, pair it with a glass of milk. (5)

Magnesium and Sleep

Evidence suggests that Mg blocks N-methyl-D-aspartate (NMDA) receptors and positively affects γ-aminobutyric acid (GABA) activity to help regulate sleep. Mg may also promote relaxation, increase melatonin and renin levels, and reduce cortisol levels. Lastly, Mg may help regulate the circadian rhythm and cellular timekeeping. (13)

The systematic review and meta-analysis conducted by Al Wadee et al. (2022) noted an association between lower serum Mg levels in patients with obstructive sleep apnea. However, the study included no inclusion of dietary and/or supplemental Mg data. (14)

The systematic review by Arab et al. (2023) included nine studies and found an association in adult human observational studies between increased Mg with improved sleep quality, whereas randomized control studies (RCT) did not. The observational studies measured Mg as dietary intake or as a urinary marker. The RCT trials evaluated dietary or supplemental Mg (upwards of 1800 mg/day). Participants across the nine studies were aged 18-80 years, one study evaluated dialysis patients, university dietetic students, those with self-reported or evaluated sleep symptoms, and/or insomnia. The varied and disagreeing results make sense given the varied populations studied. (13)

Mah and Pitre (2021) conducted a systematic review and meta-analysis (ultimately included three RCTs) evaluating older adults, oral Mg supplementation, and insomnia. Mg was provided daily for 2-8 weeks, in doses of 320-729 mg elemental Mg, and in different forms (oxide or citrate). They found that “the true effect of magnesium supplementation on insomnia symptoms lies somewhere between a positive effect and a null effect in comparison to sleep parameters and questionnaires. The clinical significance of these findings, such as an improved sleep onset latency time of 17.36 [minutes] is debatable.” (15)

The systematic review by Rawji et al. (2024) analyzed 15 studies, eight of which focused on the effect of Mg and sleep quality, and three were already accounted for in the Mah and Pitre (2021) review. For the five unaccounted for studies: (16)

• Gholizadeh-Moghaddam et al. (2022) found no difference between placebo and treatment groups (250 mg Mg oxide per day for 10 weeks). Sixty-four females aged 18-45 years were studied.

• Saba et al. (2022) found that sleep quality improved per the PSQI in those taking 500 mg Mg oxide daily for five days. Sixty hospitalized adults undergoing heart surgery aged 70 years or younger were studied.

• Hornyak et al. (1998) studied 10 patients with Periodic Limb Movements of Sleep (PLMS) or mild-to-moderate Restless Leg Syndrome. Mg supplementation significantly reduced arousal events per hour and improved sleep efficiency. The Mg oxide dose was 291.6 mg consumed daily for 4-6 weeks.

• Hornyak et al. (2004) found the supplemental group had significant increases in slow-wave sleep, renin, and aldosterone levels alongside decreased cortisol levels. The supplement contained 243 mg Mg oxide and was consumed daily for 20 days. Twelve healthy Elderly participants were studied.

• Macian et al. (2022) found that sleep quality, serum Mg, and RBC Mg did not improve with 100 mg Mg chloride taken daily for four weeks. Seventy-six adults with fibromyalgia experiencing moderate to severe stress were studied.

Hausenblaus et al. (2024) evaluated healthy adults with non-clinical insomnia symptoms, but self-defined themselves as having sleep issues. The goal was to evaluate sleep quality and daily function. Researchers compared a placebo to Mg L-threonate, two pills daily for 21 days, consumed two hours before bedtime (each containing 75 mg/g elemental Mg). The Oura ring was used to provide objective data. Neither baseline labs nor diet were evaluated for Mg. Although Oura data showed improvements in sleep stages for the Mg group (e.g., light sleep, REM sleep, deep sleep), there are sleep researchers who have mentioned sleep trackers aren’t great at parsing total sleep time into validated, reliable sleep stages. The Mg group scored significantly better in sleep quality, sleep latency (although by ~1 minute), mental alertness, mood and less morning time grouchiness, readiness score and activity balance, and activity score. The placebo group showed improvements for about the first week of the study and then plateaued, whereas the Mg group continued to optimize. The researchers noted that other studies have shown a strong placebo effect with Mg studies, too. (17)

Langan-Evans et al. (2023) conducted a crossover trial to evaluate a supplement’s effect on sleep, measured both objectively and subjectively, and collected urine to evaluate biomarkers. The supplement contained 300 mg Mg (form unlisted), 1,000 mg tryptophan, 3,000 mg glycine, 220 mg tart cherry powder, and 200 mg L-theanine. At baseline, diet was evaluated, but the article only listed calorie and macronutrient intakes. Significant improvements in sleep onset latency, total sleep time, and sleep efficiency existed for the supplemental phase of the crossover trial. However, Mg was part of a supplemental blend, so it’s difficult to say if Mg on its own led to some or all of the improvements (this was also called out as study limitation by the authors). (18)

Lastly, Zhang et al. (2022) evaluated the dietary and supplemental Mg content of those in the Coronary Artery Risk Development in Young Adults (CARDIA) study, using data over a 20-year period from 1985-2006 and a total of 3,964 participants. Participants were split into quartiles based on their Mg intake, from lowest (reporting 96.2-112.2 mg Mg/1000 kcal) to highest (182.9-223.4 mg Mg/1000 kcal). Researchers ran different models of the data and found the following:

• Those with the highest Mg intakes had better sleep quality: This Model accounted for age, race (black or white), gender, age, and one’s geographical location.

• However, once education level, current smoking status, alcohol consumption, physical activity, body mass index (BMI), and other dietary factors were accounted for (e.g., energy, caffeine, zinc, vitamin D, and carbohydrates), the relationship between Mg and sleep quality weakened to “borderline significant”.

• Regarding sleep duration, higher Mg intakes showed a smaller likelihood of sleeping for less than seven hours per night. (19)

Magnesium and Muscle Recovery

Above I walked through the Reno et al. (2022) and Steward et al. (2019) studies. Both did show improvements with either Mg glycinate or Mg oxide-and-stearate, but both studies were done in participants with low-Mg diets. It’s hard to say if Mg repletion was the mover.

Two other studies conducted by Cordova et al. in 2017 and 2019 reviewed Mg and muscle recovery.

The 2017 study is behind a paywall, so I’m working with the abstract and how other researchers have summarized it. In this study, 12 elite basketball players with an average age of 25.4 years participated in a basketball training program from October to April. Participants underwent 2-hour morning gym workouts and 3-hour afternoon practices. They received a daily dose of 400 mg Mg lactate. Another 12 university-aged recreational basketball players, but although it’s unclear, it doesn’t seem as if they received the Mg supplements. Blood was drawn four times throughout the study in 8-week intervals to evaluate serum Mg and markers of muscle damage (creatinine, urea, CK, LDH, AST, ALT, aldolase, and total protein). At the end of the study, only serum creatinine significantly decreased after the second blood draw and then significantly increased after the third and fourth. No other markers of muscle damage were affected by the Mg supplementation, which showed an increase in serum Mg levels. (20)

For the 2019 study, 18 professional cyclists competed in a 21-day cycling stage race. The goal was to evaluate if 400 mg of supplemental Mg oxide taken daily could prevent muscle damage in the nine cyclists receiving the treatment. The other nine did not. A dietitian reviewed the diets of all participants and found the average dietary Mg intake was 247+/-5.3 mg/1000 kcal—meaning they all met the RDA for Mg. This study allowed researchers to understand the above-and-beyond effects of supplemental Mg. All participants also received a daily supplement containing 10 mg folic acid, 1000 mg vitamin C, 1000 ug vitamin B-12, branched-chain amino acids (3.6 g leucine and 0.9 g each valine and isoleucine), and 1000 mg glutamine. Bloodwork was collected at baseline, halfway through the race, and at the race’s end. Serum and RBC Mg decreased for both groups, but took a less significant decline in the Mg group. There were no significant changes to white blood cells, platelets, RBC, hemoglobin, or hematocrit, and cortisol levels (a stress marker) rose for both groups while remaining within the normal range. Performance between groups showed no significant differences. All of this means that when Mg intake rises above the RDA, it may not matter for performance, cortisol, or other markers. (21)

For further reading on Mg and exercise performance, review Souza et al. (2023).

Key Takeaways

Overall, there are a few forms of Mg shown to have greater bioavailability (L-threonate and gluconate+milk) and others crossing the BBB at higher rates (L-threonate)—albeit all in rat studies. When supplementing, I would prioritize the L-threonate/Magtein® option for these reasons.

In practice I think the more useful evaluation of magnesium, and as it pertains to my role as the dietitian hoping to improve the athlete’s health and sleep, I would still use the serum and RBC Mg, but alongside evaluations of the athlete’s typical dietary and supplemental intake—and would place more emphasis on their intake over biomarkers.

My other takeaway is that in the presence of measured symptoms of poor sleep or clinically-diagnosed insomnia, Mg supplementation may be effective.

Ultimately, in the otherwise healthy athlete, focus your attention first with improving an athlete's dietary Mg, as high-Mg sources include nuts, seeds, soybeans, beans, potatoes, rice, fortified breakfast cereals, and oats. If concerned with sleep, consider improving their sleep hygiene with a relaxing bedtime routine, reducing screen time and blue light exposure closer to bed, and promoting a quiet, dark, and cool sleeping environment.

References

(1) National Institutes of Health Office of Dietary Supplements. (2022, June 2). Magnesium. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/

(2) Jeukendrup, A., & Gleeson, M. (2024). Sport Nutrition, fourth edition. Human Kinetics.

(3) Costello, R., Rosanoff, A., Nielsen, F., & West, C. (2023). Perspective: call for re-evaluation of the tolerable upper intake level for magnesium supplementation in adults. Adv Nutr,14(5):973-982. https://pubmed.ncbi.nlm.nih.gov/37487817/

(4) Harvard T.H. Chan School of Public Health. (2023, March). Magnesium. https://nutritionsource.hsph.harvard.edu/magnesium/

(5) Gropper, S.S., Smith, J.L., & Carr, T.P. (2022). Advanced nutrition and human metabolism, eighth edition. Boston, MA: Cengage.

(6) Razzaque, M.S. (2018). Magnesium: are we consuming enough? Nutrients,10(12):1863. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6316205/ 

(7) Workinger, J.L., Doyle, R.P., & Bortz, J. (2018). Challenges in the diagnosis of magnesium status. Nutrients,10(9):1202. https://pmc.ncbi.nlm.nih.gov/articles/PMC6163803/

(8) Liu, G., Weinger, J.G., Lu., Z.-L., Xue, F., & Sadeghpour, S. (2016). Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis,49(4):971-990. https://pubmed.ncbi.nlm.nih.gov/26519439/

(9) Reno, A.M., Green, M., Killen, L.G., O’Neal, E.K., Pritchett, K., & Hanson, Z. (2022). Effects of magnesium supplementation on muscle and performance. J Strength Cond Res,36(8):2198-2203. https://pubmed.ncbi.nlm.nih.gov/33009349/

(10) Steward, C.J., Zhou, Y., Keane, G., Cook, M.D., Liu, Y., & Cullen, T. (2019). One week of magnesium supplementation lowers IL-6, muscle soreness and increases post-exercise blood glucose in response to downhill running. Eur J Appl Physiol,119(11-12):2617-2627. https://pubmed.ncbi.nlm.nih.gov/31624951/

(11) Slutsky, I., Abumaria, N., Wu, L.J., Huang, C., Zhang, L., … & Liu, G. (2010). Enhancement of learning and memory by elevating brain magnesium. Neuron,65(2):165-77. https://pubmed.ncbi.nlm.nih.gov/20152124/

(12) Zhang, C., Hu, Q., Li, S., Dai, F., Qian, W., … & Wang, Y. (2022). A Magtein®, magnesium L-threonate, -based formula improves brain cognitive functions in healthy Chinese adults. Nutrients,14(24): 5235. https://www.mdpi.com/2072-6643/14/24/5235#

(13) Arab, A., Rafie, N., Amani, R., & Shirani, F. (2023). The role of magnesium in sleep health: a systematic review of available literature. Biol Trace Elem Res,201(1):121-128. https://pubmed.ncbi.nlm.nih.gov/35184264/

(14) Al Wadee, Z., Ooi, S.L., & Pak, S.C. (2022). Serum magnesium levels in patients with obstructive sleep apnoea: a systematic review and meta-analysis. Biomedicines,10(9):2273. https://pubmed.ncbi.nlm.nih.gov/36140382/

(15) Mah, J., & Pitre, T. (2021). Oral magnesium supplementation for insomnia in older adults: a systematic review & meta-analysis. BMC Complement Med Ther,21(1):125. https://pubmed.ncbi.nlm.nih.gov/33865376/

(16) Rawji, A., Peltier, M.R., Mourtzanakis, K., Awan, S., Rana, J., … & Afzal, S. (2024). Examining the effects of supplemental magnesium on self-reported anxiety and sleep quality: a systematic review. Cureus,16(4):e59317. https://pubmed.ncbi.nlm.nih.gov/38817505/

(17) Hausenblaus, H.A., Lynch, T., Hooper, S., Shrestha, A., Rosendale, D., & Gu, J. (2024). Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized control trial. Sleep Med X,8:100121. https://pubmed.ncbi.nlm.nih.gov/39252819/  

(18) Langan-Evans, C., Hearris, M.A., Gallagher, C., Long, S., Thomas, C., … & Morton, J.P. (2023). Nutritional modulation of sleep latency, duration, and efficiency: a randomized, repeated-measures, double-blind deceloption study. Med Sci Sports Exerc,55(2):289-300. https://pubmed.ncbi.nlm.nih.gov/36094342/

(19) Zhang, Y., Chen, C., Lu, Liping, Knutson, K.L., Carnethon, M.R., … & Kahe, K. (2022). Association of magnesium intake with sleep duration and sleep quality: findings from the CARDIA study. Sleep,45(4):zsab276. https://pubmed.ncbi.nlm.nih.gov/34883514/

(20) Córdova, A.M., Fernández-Lázaro, D., Mielgo-Ayuso, J., Seco Calvo, J., & García, A.C. (2017). Effect of magnesium supplementation on muscular damage markers in basketball players during a fall season. Magnes Res,30(2):61-70. https://pubmed.ncbi.nlm.nih.gov/28816171/

(21) Córdova, A.M., Mielgo-Ayuso, J., Roche, E., Caballero-Garcia, A., & Fernández-Lázaro, D. (2019). Impact of magnesium supplementation in muscle damage of professional cyclists competing in a stage race. Nutrients,11(8):1927. https://www.mdpi.com/2072-6643/11/8/1927