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Get startedI'm a magnesium supplement expert – here are five things I'd never do when buying
As Which?'s resident nutrition and supplement expert, I've learnt plenty from our recent review of magnesium supplements. Here's what you need to know – and what to avoid
I've spent many hours reviewing magnesium supplements to uncover the best options to buy.
From poring over ingredient lists to analysing every last milligram of their contents – and giving myself a headache trying to decipher the small print on bottle labels and packaging – I've ended up with a really good sense of what's out there and the pitfalls you can fall into when choosing.
I've learnt that spending more doesn't always pay off, that big brands can be surprisingly disappointing, and dosage can vary significantly – which can make some products far more expensive over time than you think they are.
Get the lowdown below on the five things I wouldn't do when choosing magnesium supplements, or head straight to our magnesium supplement reviews for our top picks.
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1. I wouldn't treat magnesium as a magic sleeping pill
Social media is awash with influencers assuring you that magnesium will help you sleep like a baby. But take this with a pinch of salt. Whatever anecdotes people may have, magnesium doesn't work like a sleeping pill, and at the moment there is still no good evidence at all that it will help you sleep.
That's not to say don't try it, but don't get too swept up in the hype either.
We do know that magnesium is essential for many functions in the body, including healthy muscles, nerves, bones and even the regulation of blood sugar. It is also known to help reduce tiredness (subtly different to helping you sleep!).
As for sleep, the theory is that magnesium promotes relaxation through its role in the brain in regulating neurotransmitters, as well as supporting the production of melatonin, and can therefore help you drift off. However, the evidence for this is still very thin. One systematic review in 2021 set out to evaluate whether magnesium supplementation can benefit older people with insomnia, but only found three studies, one of which involved just 12 participants.
Other studies have proved inconclusive, or they contradict each other. It may be that there is a plausible mechanism by which magnesium could help calm the nervous system and relax muscles, making it easier to fall asleep and stay asleep, but more research is needed.
2. I wouldn't go straight for supplements before taking a good look at my diet
I know I might sound like a broken record, but you can't out-supplement a poor diet, so don't just reach straight for the pill pack in the hope of an easy fix.
While some people find supplements a helpful addition, or that they correct a deficiency, it's always better to assess what you're eating first and think about ways to add in more magnesium-rich foods if they are lacking. Trying this first could save you money in the long run.
Spinach, nuts (especially almonds, cashews and Brazil nuts), seeds (especially sesame, chia and pumpkin seeds), potatoes, whole grains and cereals are good sources. Bananas and apricots also contain magnesium.
The good news is that dark chocolate does too. A 25g portion of 70-85% cocoa dark chocolate provides around 64 mg of magnesium, or about 16% of your Nutrient Reference Value (NRV).
3. I wouldn't buy a supplement without checking dose size and the type of magnesium
I was really surprised to see the variation in how many pills you need to take to get the recommended dose.
Some required just one capsule daily, while others suggested four! If you don't like swallowing big pills, or take other supplements or medications too, this is quite a lot – it would certainly make me think twice.
It has an impact on costs too, as the price per dose can shoot up the more pills you have to pop. So make sure you check this when comparing products.
I would also never skip checking the type of magnesium included.
Magnesium comes in several forms – such as magnesium citrate and bisglycinate – and these have different pros and cons. Some are more gentle on your digestive system or more bioavailable (more easily absorbed by the body) than others.
In our review of magnesium supplements we found a real mix of types and formats, and some will be more suitable or beneficial than others.
4. I wouldn't take too much
Despite what the marketing might have you thinking, more is not always better with supplements, and magnesium is no exception. Remember that you will also be getting some from your diet, so don't feel tempted to max out your supplement intake. It's not a race to the top.
The NHS recommends 300mg a day for adult men and 270mg a day for adult women. The EU-set daily reference amount (NRV) is 375mg, so this is what lots of supplements aim for.
Older adults and those with digestive tract issues can find it harder to absorb magnesium from their diets and so might benefit from a supplement.
But it's not recommended to exceed 400mg per day. Taking more than this could, in the short term, cause unpleasant side effects such as digestive issues, diarrhoea and dizziness.
In extreme cases it can cause heart irregularities and even heart failure (though serious problems from magnesium overdoses are rare).
Start at a lower dose and see how it works for you, as if it does you'll again be saving money in the long run too.
5. I wouldn't take all my supplements at once
Most of us probably try to remember to take our daily pills or supplements by sticking to a set routine, whether it's taking them with your morning coffee and cereal or keeping them by your bed at night. But different supplements can interact with each other and some foods, or with medication you are taking (which is why you should always check with a health professional if you are on any medication).
How and when you take a supplement can impact how effective it is too. For example, iron and calcium supplements should be taken at least two hours apart, as calcium can reduce iron absorption, and you should also stop taking supplements with biotin at least a few days before any blood tests, as it can interfere with blood test results.
With magnesium, when's best to take it depends on your goals. If you take it for energy or muscle recovery, then it may be best to take it in the morning or after exercise. Taking it with food may also help improve absorption. However, if you're taking it to help with sleep, taking it around an hour before bed is probably more effective.
Best magnesium supplements – see our independent expert reviews, which rate each product for the amount of fillers and additives, as well as dose and bioavailability
Our supplements expert
Shefalee Loth, Which? principal researcher and nutritionist
Shefalee is a public health nutritionist with 20 years' experience, and has worked for the NHS, The London School of Hygiene & Tropical Medicine and World Cancer Research Fund.
At Which?, Shefalee is a principal researcher, researching and writing food and nutrition content for our magazine and website and is a media spokesperson. She is also the research lead for our health and wellbeing reviews. She is a trustee at Sustain, the food and farming alliance.
Shefalee focuses on cutting through the hype to explain what you need to know about nutrition and healthy eating and to help you choose better. From 'How bad is ultra-processed food?' to the 'Top gut health myths you need to know about' and 'What really works to cut cholesterol', she gives no-nonsense advice to help you make healthier choices and save money.
