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Quick answer
Magnesium is an essential mineral involved in nerve and muscle function. Small studies, mostly in older adults, suggest magnesium supplements might help people fall asleep a little faster, but a 2021 systematic review rated the evidence as low quality and the benefit as uncertain. People most likely to benefit are those who don't get enough magnesium from their diet.
Magnesium supplements are safe for most healthy adults at sensible doses. Too much causes diarrhoea, and people with kidney disease should not take them without medical advice.
Why magnesium is linked to sleep
Magnesium plays a role in calming the nervous system. It helps regulate GABA, the brain's main calming chemical messenger, and dampens the activity of excitatory pathways. It is also involved in muscle relaxation and in the body's stress-hormone system.
Low magnesium levels have been linked in observational studies to poorer sleep and higher stress and anxiety scores. However, an association does not prove that taking a supplement will help someone whose magnesium levels are already adequate.
What the research says
Sleep
- A 2021 systematic review in BMC Complementary Medicine and Therapies looked at randomised trials of magnesium for insomnia in older adults. Magnesium shortened the time to fall asleep by about 17 minutes compared with placebo in pooled results, but there were only three small trials and the evidence was rated low quality.
- One frequently cited trial in elderly people with insomnia found that 500 mg of magnesium a day for eight weeks improved several sleep measures.
- Trials in younger adults are scarce, and studies combining magnesium with melatonin or zinc make it hard to tell which ingredient helped.
Stress and anxiety
Reviews suggest magnesium might help mild anxiety, particularly in people with low magnesium, but the studies are small and of variable quality.
Muscle cramps
Despite popular belief, a Cochrane review found that magnesium is unlikely to prevent typical night-time leg cramps in older adults.
Which type of magnesium is best?
Supplements combine magnesium with another compound, which affects how well it is absorbed and how likely it is to upset the stomach:
- Magnesium glycinate (bisglycinate): well absorbed and gentle on the stomach. Often marketed for sleep, though there is no direct evidence it works better for sleep than other forms.
- Magnesium citrate: well absorbed, but has a mild laxative effect.
- Magnesium oxide: cheap and contains a lot of magnesium per tablet, but is poorly absorbed and more likely to cause diarrhoea. It was used in some sleep trials.
- Magnesium threonate: marketed for the brain; human evidence is very limited.
In short, choose a form that agrees with your stomach. Glycinate or citrate are good starting points.
How to use it
- Start with food. Good sources include pumpkin seeds, almonds, cashews, spinach, black beans, whole grains, dark chocolate and avocado. The recommended daily intake for adults is about 310 to 420 mg, depending on age and sex.
- If you take a supplement, a typical dose is 100 to 350 mg of elemental magnesium in the evening. Check the label for "elemental" magnesium, which is the actual amount of the mineral.
- Don't exceed 350 mg a day from supplements without medical advice. This is the upper limit set by the US National Institutes of Health for adults; it does not include magnesium from food.
- Give it 2 to 4 weeks, alongside good sleep habits, and stop if you notice no difference.
Possible side effects and interactions
- Digestive upset: diarrhoea, cramping and nausea are common at higher doses, especially with oxide and citrate.
- Too much magnesium: very high intakes, particularly in people with kidney problems, can cause low blood pressure, muscle weakness, confusion and irregular heartbeat.
- Interactions: besides the medicines above, some diuretics and acid-reducing medicines (proton pump inhibitors) can change magnesium levels.
Who should avoid it
- People with kidney disease, who may not be able to clear excess magnesium
- People with heart block or myasthenia gravis, unless supervised
- Anyone taking the interacting medicines above should plan timing with their pharmacist
- Pregnant women should use supplements only on a doctor's advice
When to see a doctor
See a doctor if:
- Sleep problems have lasted more than three months or are affecting your daytime functioning
- You snore loudly or wake up gasping, which can be signs of sleep apnoea
- Stress or anxiety is affecting your work, relationships or mood most days
- You have symptoms that could point to low magnesium or other conditions: muscle twitches, tremors, irregular heartbeat or unusual weakness
- You take diuretics or proton pump inhibitors long term and have symptoms of low magnesium; a blood test may be needed
Cognitive behavioural therapy for insomnia (CBT-I) is the most effective long-term treatment for chronic insomnia, and it is worth asking about.
Frequently asked questions
When should I take magnesium for sleep?
Most people take it about an hour before bed. There is no strong evidence that timing matters, but taking it with an evening meal may reduce stomach upset.
Can I take magnesium every night?
Daily use within the recommended limits is generally safe for healthy adults. If you have kidney problems or take regular medicines, check with your doctor first.
Will magnesium make me drowsy the next day?
It is not a sedative and usually doesn't cause morning grogginess.
Do magnesium sprays and bath salts work?
There is little evidence that magnesium is absorbed in meaningful amounts through the skin. A warm bath before bed may help you relax regardless.
References
- NIH Office of Dietary Supplements. Magnesium: fact sheet for health professionals. https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies, 2021.
- Abbasi B, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences, 2012.
- Garrison SR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 2020.
