Melatonin or Magnesium: what is the difference

In queries about «sleep supplements» melatonin and magnesium take the top places, and they are often compared as if they were two versions of the same substance. In reality melatonin is a hormone that conveys the «night» signal to the internal clock, and magnesium is a mineral needed for the work of hundreds of enzymes and the neuromuscular system. The editorial team explains how their action fundamentally differs.

Different nature of the substances

Melatonin is a neurohormone that the body produces itself in the pineal gland. Its level fluctuates throughout the day: minimal during the day and high at night. Taking melatonin externally imitates this nighttime signal.

Magnesium is an essential mineral that the body does not synthesize and must obtain from food. It is not a sleep signaling molecule: its significance for sleep is indirect and manifests primarily when the mineral is lacking.

From this difference follows the main point: melatonin acts «on demand» — within hours of intake, while magnesium works as part of the body's basic provision, and its contribution to sleep accumulates gradually with the correction of status.

Another difference is regulatory. In many EU countries melatonin of certain forms and doses is sold only by prescription, whereas magnesium is an ordinary food supplement almost everywhere.

How melatonin works

Melatonin binds to MT1 and MT2 receptors in the suprachiasmatic nucleus of the hypothalamus and other tissues. Through MT1 it suppresses the activity of neurons that maintain wakefulness, and through MT2 it shifts the phase of the circadian rhythm.

The time of intake determines the effect. Melatonin taken a few hours before the usual time of falling asleep shifts the rhythm earlier, while taken in the morning it can shift it later. Therefore, for correcting the schedule, not only «what» but also «when» is important.

In the ordinary form melatonin is quickly absorbed and just as quickly eliminated: the half-life is about an hour. Prolonged-release forms are created to maintain the concentration through most of the night.

The meta-analysis by Ferracioli-Oda et al. (2013) showed that in primary sleep disorders melatonin shortens the time to fall asleep and slightly increases sleep duration, although the absolute effect is small.

How magnesium is connected to sleep

Magnesium affects the nervous system in several ways. It blocks the channels of NMDA receptors at rest, reducing excessive excitation, modulates calcium channels and takes part in the regulation of muscle tone.

With a magnesium shortfall neuromuscular excitability rises, cramps, twitching, irritability may appear. All this is capable of worsening falling asleep and sleep continuity, so correcting a shortfall can indirectly improve sleep.

Direct data on the effect of magnesium on sleep is limited. Abbasi et al. (2012) reported an improvement in insomnia indicators in older people, and the systematic review by Mah and Pitre (2021) rated the quality of evidence as low.

In people without a deficiency additional magnesium is unlikely to give a noticeable «hypnotic» effect. This is an important difference from melatonin, which acts through receptors regardless of whether there is a «shortfall» of the hormone.

Comparison by key parameters

We have summarized the main differences in a table to make them easy to compare.

Interestingly, both substances have also been studied together. Rondanelli et al. (2011) studied a combination of melatonin, magnesium and zinc in older residents of care homes with insomnia and reported an improvement in sleep indicators. However, the separate contribution of each component cannot be assessed from such a design.

Thus, comparing melatonin and magnesium «by strength» is not quite correct: they work at different levels and can be appropriate for different causes of poor sleep.

Safety and interactions

Melatonin in short-term use is well tolerated but can cause morning drowsiness, dizziness and headache. It interacts with anticoagulants, immunosuppressants, fluvoxamine and other medications.

Magnesium from supplements in doses over 350 mg per day more often causes a laxative effect. For people with chronic kidney disease magnesium supplements are contraindicated without a doctor's supervision because of the risk of accumulation.

• Magnesium reduces the absorption of tetracyclines, fluoroquinolones and bisphosphonates.
• Melatonin should not be combined with alcohol and sleeping pills without a doctor.
• The melatonin content in supplements may differ from what is stated — choose proven manufacturers.
• Pregnant women and children should take melatonin only on a doctor's recommendation.

Neither substance is a treatment for chronic insomnia. Clinical guidelines put cognitive behavioral therapy first, and consider supplements as auxiliary means in particular situations.

Editorial conclusions

Melatonin is a hormonal signal for the internal clock that acts within hours of intake. Magnesium is a mineral whose shortfall can worsen sleep and whose correction gives a gradual effect.

For problems with the schedule and jet lag melatonin is more appropriate; for people with signs of a magnesium shortfall or muscle cramps — magnesium after assessing the diet.

In people without a deficiency magnesium is unlikely to noticeably affect sleep, and melatonin does not eliminate the causes of chronic insomnia.

We also recommend our materials on choosing between melatonin and magnesium for different situations, on the forms of magnesium and on melatonin and glycine.

References

1. Ferracioli-Oda E, Qawasmi A, Bloch MH. Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One. 2013;8(5):e63773.
2. Rondanelli M, Opizzi A, Monteferrario F, Antoniello N, Manni R, Klersy C. The effect of melatonin, magnesium, and zinc on primary insomnia in long-term care facility residents in Italy: a double-blind, placebo-controlled clinical trial. J Am Geriatr Soc. 2011;59(1).
3. Abbasi B, Kimiagar M, Sadeghniiat K, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. J Res Med Sci. 2012;17(12):1161–1169.
4. Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review & meta-analysis. BMC Complement Med Ther. 2021;21(1):125.
5. de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1–46.
6. Sateia MJ, Buysse DJ, Krystal AD, Neubauer DN, Heald JE. Clinical practice guideline for the pharmacologic treatment of chronic insomnia in adults: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2017;13(2):307–349.