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3rd February, 20215 min read

Magnesium supplements: benefits and side effects

Medical reviewer:Dr Adiele Hoffman
Author:Helen Prentice
Last reviewed: 18/02/2021
Medically reviewed

All of Healthily's articles undergo medical safety checks to verify that the information is medically safe. View more details in our safety page, or read our editorial policy.

In order for your body to work properly, it’s important to get the right nutrients, and eating a healthy, balanced diet should help you get all the vitamins and minerals you need.

However, there’s a huge number of dietary supplements available from pharmacies, supermarkets and the internet.

One of these supplements is magnesium – but are all the claims made about magnesium correct? Can these ‘super pills’ really help with tiredness, muscle tension and sleeping problems?

As with many supplements, there isn’t much scientific evidence to back up such claims. So it’s a good idea to make sure you’re as informed as possible before deciding whether to take magnesium.

Read on to learn what magnesium is and why our bodies need it, whether you might be deficient in magnesium, and if supplements can help.

What is magnesium?

Magnesium is a mineral that has several important jobs. It helps your body to turn the food you eat into energy, plays a role in keeping your bones and teeth healthy, and helps your nerves and muscles to work properly.

Magnesium is found in lots of foods, including:

  • green vegetables
  • pulses – peas, beans and lentils
  • wholegrain bread and cereals
  • meat
  • nuts

How much magnesium do I need?

The recommended daily intake of magnesium differs in different countries. It also depends on your age and gender. So, in the US, for example, it's 310-320mg a day for women and 400-420mg a day for men. In the UK, it's 270mg for women and 300mg a day for men.

If you’re not getting enough magnesium on a regular basis, it can lead to a magnesium deficiency in the blood – this is known as ‘hypomagnesaemia’.

Could I have a magnesium deficiency?

If you’re generally healthy and eat a balanced diet, it’s unlikely that you have a magnesium deficiency. This is because your kidneys are very good at stopping magnesium from being lost when you pee, so your levels stay balanced.

However, some things can make a deficiency more likely, including digestive disorders (such as chronic diarrhoea or coeliac disease), certain medications (such as antibiotics) and consuming large amounts of alcohol.

Hypomagnesaemia can cause various symptoms, but the most common include:

  • feeling or being sick (nausea or vomiting)
  • muscles spasms
  • tremors
  • sleepiness
  • weakness
  • loss of appetite
  • seizures – in severe cases and particularly in children
  • irregular heartbeat

If you have these symptoms, or you’re worried about your magnesium levels, speak to your doctor – they can arrange a blood test to check for any deficiencies.

Can magnesium supplements help me?

While magnesium supplements are sometimes marketed as being able to help with various health issues, including fatigue, muscle tension, and insomnia, there isn’t scientific proof to back up these claims.

You should usually be able to get all the magnesium you need from your diet. When there are risk factors for deficiency, such as those mentioned above, a supplement may be needed – but you should check with your doctor first, particularly if you have other health issues.

If your doctor recommends magnesium, they will be able to tell you how to take it and what dose you should have.

Do magnesium supplements have side effects – and can I take too much?

When you get magnesium from food – by eating lots of green vegetables and wholegrain bread, for example – if you have too much, it’s filtered out by your kidneys and leaves your body when you pee.

However, it’s possible to get too much magnesium if you have it in supplement form. The most common side effect is diarrhoea, and sometimes nausea and tummy cramps, too. If magnesium is taken in very large doses, in rare cases it can cause toxicity, which is a medical emergency.

For these reasons, you should not take magnesium supplements if you have kidney problems, unless recommended by your doctor, as you may not be able to remove any excess magnesium from your body.

Magnesium supplements can also interfere with other medicines, including some osteoporosis medications and antibiotics. If you’re taking any other medicines, remember to talk to your doctor before taking magnesium supplements.

When to see a doctor

Whether you have symptoms that suggest a magnesium deficiency or you’re just considering topping up your levels with a supplement, it’s best to speak to your doctor first. They may suggest a blood test to measure the amount of magnesium in your body and check for any deficiencies.

Key points

  • magnesium is a mineral that helps turn food into energy and keep bones, muscles and nerves healthy
  • magnesium deficiency in healthy people is not common
  • symptoms of deficiency include nausea, vomiting and muscle spasms
  • excess magnesium is removed by your kidneys, but taking too much in a supplement can cause diarrhoea and tummy cramps
  • don’t take magnesium supplements if you have kidney disease, unless they’re prescribed by a doctor
  • magnesium supplements may also interfere with some medicines
  • it’s best to speak to your doctor before taking magnesium supplements
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