Is it worth buying magnesium to improve your sleep? Here's my detailed review of the evidence.. or you could watch the video on YouTube for the full version!
Why is magnesium important?
Magnesium is like the swiss army knife of the mineral world. You name it - if it’s important in the body and brain - magnesium probably helps to make it happen more efficiently.
It helps maintain the normal function of our cells, enabling energy production, protein synthesis DNA repair and replication
It’s built into the infrastructure of bones and teeth
It enables nerve conduction and neurotransmitter synthesis, not just in the body, but also in the brain, facilitating learning, memory, and helping to moderate our stress response
It helps maintain healthy blood sugar levels and keeps the heart beating regularly
It supports the immune system, decreasing harmful inflammation, and reducing oxidative stress
So, unsurprisingly, a lack of magnesium is a risk factor for the development and progression of a bunch of chronic illnesses including diabetes, heart disease, high blood pressure, osteoporosis, dementia and even early mortality.
Do you get enough magnesium in your diet?
We all need Magnesium - the body can’t make it - we rely on what we eat.
The good news is that Magnesium is found in a lot of foods.
Rich sources include most foods with high fibre content
Leafy vegetables
Legumes or pulses
Nuts
Seeds
Avocados
Bananas, kiwis
whole grains
Fish and meat
It’s also added to some cereals and mineral waters.
Recommendations for how much magnesium we need vary by country, but as a minimum, it’s around 5 to 7mg/ kg of body weight - so at least 300mg per day for women, 400mg for men.
What happens if we have too much magnesium?
The body is really good at balancing our intake of magnesium with the amount we excrete from the body. Let’s say we consume 360mg in our diet, whether that’s through meals or supplements.
30-40% of it will be absorbed as it travels through the small and large intestine.
More than half of it will likely be pooped out of the other end.
So we could have around 100mg which makes its way into the body, at least temporarily
Of this, only a tiny fraction - <1% - will be detectable in the blood as serum magnesium.
The rest is soaked up and used within our cells.. We store around 25g of magnesium in the body at any one time -
50-60% is in our bones and teeth
30% in our muscles
And 10-20% in the brain and other tissues
Any magnesium we don’t need is filtered out by the kidneys and excreted in our urine - in this case around 100mg/day to maintain our balance.
So if you’re generally healthy, it’s highly unlikely that you will suffer from hypermagnesaemia, or too much magnesium. It does happen in kidney failure though, and signs of include weakness, confusion, low breathing rate, poor reflexes and cardiac arrest.
What causes magnesium deficiency?
So, most of us don’t need to worry about too much magnesium, but what about too little?
Low levels of magnesium can be caused by putting too little in, not absorbing enough, or excreting too much.
If you persistently eat a diet which is low in fibre and high in ultra processed foods, over time, this will put you at greater risk of magnesium deficiency.
Chronic conditions such as diabetes, GI disorders and kidney problems will often upset the magnesium balance by unhelpfully altering absorption or excretion.
Other factors that can lower magnesium retention include:
Diets unusually high in sodium, calcium or protein
Excessive caffeine, or Alcohol - or both,
And Drugs including diuretics, antacids and antibiotics
Even if you have a model diet - Pregnancy, menopause and ageing can all increase the risk of magnesium deficiency. Research has shown that people who do a lot of endurance exercise are more likely to be short of magnesium. In fact, being exposed to any kind of chronic stressor may reduce our magnesium reservoir - exams, noise, cold, AND lack of sleep have been found to increase the rate of excretion of magnesium into the urine. Over time, chronic exposure to stress could increase the risk of magnesium deficiency.
But hang on a minute.. Didn’t we say earlier that we need magnesium to keep our stress response in check?
Good point. Well remembered.
Magnesium is a cofactor in a heap of stress-busting reactions, including:
- the production and transmission of mood boosting Serotonin,
- activating calming GABA receptors, and
- reducing cortisol levels in the body
So.. if chronic stress lowers our stress-busting magnesium reserves.. There is potential for a vicious cycle, where the magnesium-deprived brain and body is then more susceptible to the damaging effects of stress. Low magnesium levels have been linked to depression, anxiety and other mental health disorders.
How do you know if your magnesium levels are low?
OK, this sounds like I should just get a blood test for Magnesium?
Mmm. Not so fast. Measuring Magnesium in blood is notoriously unhelpful.
Only 0.3% of the body’s magnesium is in the serum. The vast majority of it is in the bones and tissues. Our bodies work so hard to maintain blood levels within a narrow window (0.7–1 mmol/L), using the body’s stores as a buffer, that you could have apparently healthy levels in the blood which still mask a moderate to severe Magnesium deficiency.
For this reason, research studies will use food diaries over several days to estimate dietary magnesium intake. This is time consuming and relies on recall which may not be accurate, but seems to be more closely linked to health outcomes than serum magnesium.
So your best bet could be to keep a food diary for a few days and use online nutrient tables to tot up your magnesium intake.
You could measure magnesium in your red blood cells, urine, or take a magnesium tolerance test, but these tests are harder to come by.
If you eat a broadly healthy diet, with plenty of whole foods, and you don’t have any GI or kidney issues, you’ve probably got a hearty stash of magnesium.
But large scale studies suggest anything from 10 to 60% of the general population are not getting enough magnesium in their diet, depending on the country.. In the UK, young people, the elderly, those from more deprived backgrounds and those with chronic conditions are at greatest risk of magnesium deficiency.
Unfortunately, the symptoms of low magnesium are pretty non-specific, and can easily be confused for chronic stress..
Tiredness, irritability, anxiety or nervousness, GI spasms, muscle cramps, headache, and mild sleep problems
Could taking a Mg supplement improve your sleep?
OK, so now that we know a bit more about magnesium, we’re finally ready to answer the question I started with… Will taking a magnesium supplement improve your sleep?
And in true scientific fashion, my answer is, ‘it depends’
If you’ve found any of my other videos you’ll know that I talk about 3 major systems which influence on your sleep quality. In a nutshell, you want consistency to strengthen your circadian rhythms, you want to build up sleep pressure without letting stimulants interfere, and you’ll need to convince the stress system that it’s safe to switch off.
Magnesium potentially has multiple soothing effects on the stress system, but it’s likely that a supplement will only help if you’re correcting a deficiency, and it could take a few weeks.
If you’ve noticed an immediate overnight benefit from a magnesium supplement, it may be because of the placebo effect. If you believe something will help you sleep, your anxiety about not being able to sleep reduces, and you fall asleep faster, and stay asleep for longer. This isn’t necessarily a problem - it’s great news - but it doesn’t tell us whether magnesium is the active ingredient.
For that, we need to compare magnesium to a placebo, in a randomized controlled trial.
There have been a handful of this type of trial. A meta-analysis published in 2021 combined the results of 3 trials in 151 adults over the age of 55 - so all quite small studies. They found that on average magnesium helped people fall asleep 17 minutes faster, but didn’t have consistent effects on sleep quality or total sleep time.
One study that is often cited as evidence that magnesium helps people sleep better gave 46 adults over 60 years of age 500mg of magnesium, as magnesium oxide, for 8 weeks, compared to placebo. Although they fell asleep faster after 8 weeks, they still took over an hour to fall asleep at the end of the trial. Sleep quality improved by 2 points on the Insomnia Severity Index; a change of 6 points would usually be recognised as a clinically significant improvement.. In other words, things improved a bit, but not much.
A more recent review explored the effects of magnesium supplements on self-reported anxiety and sleep quality. They found that 5 out of 8 studies reported sleep improvements, 2 studies found no improvements and 1 had mixed results.
Of the better quality studies, one was a randomized placebo controlled trial in 46 women with polycystic ovary syndrome. Magnesium had no significant effects on sleep quality .
The authors commented that most studies were small, some combined magnesium with other supplements like B6 or L-Theanine, so it was hard to draw conclusions.. BUT there were no adverse effects reported. 5 out 8 studies found improvements in self-reported anxiety.
The most frequent downside of some magnesium supplements is laxative effects or diarrhoea, but this is thought to be more of a problem with magnesium sulfate, citrate or oxide.
So… In conclusion? Am I going to buy more magnesium?
Honestly, I don’t find the evidence for magnesium supplements for sleep very compelling for me - but - I’m 43, and generally healthy, and my sleep is pretty good.
If I had diabetes, I was over the age of 55, and I was really struggling with my sleep I might well give it a go. So it depends..
BUT
While doing all this reading about magnesium, my overarching feeling was is that it does a whole load of stuff that might not benefit sleep, but that I don’t want to be magnesium deficient. It seems pretty indispensable for skeletal muscle integrity, energy production, limiting inflammation and protecting brain cells from oxidative stress.
Going forwards I will definitely be keeping an eye on my dietary magnesium intake, and I will consider a supplement as an insurance policy if I think I’m not getting enough from my diet.
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