Zinc and Sleep

Zinc is often recommended to take in the evening «for deep sleep», especially as part of ZMA. The editorial team checked what this idea is based on: what mechanisms are described in laboratory work, what studies involving people have shown, and what should not be expected from zinc.

Where the idea of zinc for sleep came from

The link between zinc and sleep spread in the sports environment primarily thanks to the ZMA formula — a combination of zinc, magnesium, and vitamin B6, which is traditionally advised to be taken before sleep. Many users report more vivid dreams and deeper sleep, and these reviews quickly cemented zinc’s reputation as a «sleep mineral».

However, ZMA simultaneously contains magnesium, whose role in regulating the nervous system has been studied much better. Therefore it is practically impossible to isolate the effect of zinc specifically in such formulas. In addition, some of the subjective sensations may be explained by the expectation of an effect and the ritual of an evening intake.

The scientific interest in the topic has another source as well. Zinc is present in high concentrations in the synaptic vesicles of some neurons of the brain, in particular in the hippocampus. From there it is released during signal transmission and modulates the work of receptors. This gave a reason to study it as a possible regulator of the state of sleep and wakefulness.

The editorial team considers it necessary to set the emphases straight away: zinc is an important trace element for the work of the nervous system, but the evidence base for improving sleep in humans is still limited. Below we will examine what exactly is known.

Mechanisms: what the laboratory data show

In the brain, zinc acts as a neuromodulator. It is able to suppress the activity of NMDA receptors associated with the excitation of nerve cells and to interact with the receptors of GABA — the main inhibitory neurotransmitter. Theoretically, this may facilitate the brain’s transition into a state of rest.

The review by Cherasse and Urade (2017) summarized data according to which, in experiments on mice, oral administration of zinc increased the duration of slow-wave sleep. The authors proposed considering zinc as one of the dietary modulators of sleep. However, they themselves emphasized that these results should be transferred to humans with caution.

There are also hypotheses about the role of zinc in the synthesis and action of melatonin — the hormone that regulates circadian rhythms. Zinc is part of the enzyme systems associated with tryptophan metabolism, but there is insufficient direct evidence that a zinc supplement changes the melatonin level in healthy people.

So biological plausibility exists, but between «plausible» and «proven in clinical trials» there is a significant distance. For practical decisions, one should rely specifically on studies involving people.

Studies involving people

There are few clinical studies in which zinc was studied in isolation as a sleep aid. The most frequently cited is the work of Rondanelli and co-authors (2011) in nursing homes in Italy. Participants with primary insomnia received a combination of melatonin, magnesium, and zinc or placebo, and in the supplement group the indicators of sleep quality improved.

However, this study used a complex of three components, so the effect cannot be attributed to zinc alone. In addition, the participants were elderly people with insomnia, not young athletes. The results are interesting but of limited applicability.

Some observational studies found a link between the concentration of zinc in serum and the duration of sleep. Observational data do not prove a cause-and-effect relationship: both sleep and zinc status may depend on the overall lifestyle, nutrition, stress, and state of health.

As for ZMA in athletes, studies mostly examined strength, body composition, and hormones, not sleep as the main outcome. Therefore the opinion that «ZMA improves sleep» rests primarily on subjective reviews.

Who should pay attention to zinc

If a person has a zinc deficiency, correcting it may have a positive effect on overall well-being, including sleep. Here the same principle applies as for other trace elements: correcting a deficiency gives an effect, while additional intake with a normal status is unlikely to.

The risk groups include people on a plant-based diet, on long low-calorie diets, with diseases of the digestive tract, and also those who regularly consume alcohol. For athletes an additional factor is a large volume of training and the loss of trace elements with sweat.

• poor sleep against the background of a strict diet — first assess the overall diet;
• frequent infections, slow healing, brittle nails — a reason to discuss zinc status with a doctor;
• insomnia lasting for weeks — a reason to consult a sleep specialist, not to look for a supplement;
• an evening intake of ZMA — keep in mind that zinc is already there, and do not duplicate it.

If a supplement is appropriate, a dose at the level of the recommended norm — about 10–15 mg of elemental zinc — is a safe choice. Zinc can be taken in the evening with food, but if it causes nausea, it is better to move the intake to another time.

Taking zinc on an empty stomach before sleep is a common recommendation for ZMA, associated with the fact that calcium and food can impair absorption. However, in some people this causes stomach discomfort, which certainly does not aid sleep.

What actually improves an athlete’s sleep

Sleep for an athlete is one of the main factors of recovery. The consensus statements of sports organizations emphasize the importance of sufficient sleep duration, a regular schedule, darkness and coolness in the bedroom, and also limiting caffeine in the second half of the day.

Caffeine in pre-workout complexes is one of the most frequent causes of poor sleep in people who train in the evening. No mineral compensates for a large dose of stimulants a few hours before sleep. Similarly, high-intensity training late in the evening can interfere with falling asleep.

Nutrition also matters. An energy deficit, especially a sharp one, often worsens sleep. A large late meal, alcohol, and an excess of fluid before sleep are a few more factors worth checking before turning to supplements.

Among supplements, the best-studied for sleep is melatonin, and among minerals — magnesium, especially in elderly people and those with low status. Zinc in this list still occupies the place of a «promising but insufficiently studied» candidate.

Editorial conclusions

Zinc participates in the work of the nervous system, and in animal models it affected the structure of sleep. However, there is still no convincing clinical evidence that a zinc supplement improves sleep in healthy people with normal status.

The popularity of zinc as a «sleep aid» is connected primarily with the ZMA formula, in which the effect may be due to magnesium or the expectation of a result.

If sleep problems are prolonged, one should start with sleep hygiene, limiting stimulants, and revising the diet, and if needed consult a doctor. Zinc makes sense in the case of a confirmed or probable deficiency.

Also read our articles «Zinc after 40», «Magnesium for Women: Are There Any Special Considerations», and «How to Choose a Quality Zinc: What to Look for on the Label».

References

1. Cherasse Y, Urade Y. Dietary zinc acts as a sleep modulator. Int J Mol Sci. 2017;18(11):2334.
2. Rondanelli M, Opizzi A, Monteferrario F, et al. 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):82–90.
3. Wilborn CD, Kerksick CM, Campbell BI, et al. Effects of zinc magnesium aspartate (ZMA) supplementation on training adaptations and markers of anabolism and catabolism. J Int Soc Sports Nutr. 2004;1(2):12–20.
4. Plum LM, Rink L, Haase H. The essential toxin: impact of zinc on human health. Int J Environ Res Public Health. 2010;7(4):1342–1365.
5. Institute of Medicine (US) Panel on Micronutrients. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington (DC): National Academies Press; 2001.
6. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.