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what is magnesium

Magnesium: functions, foods, deficiency and supplements

Find out all about magnesium, including what magnesium is good for, what it does, how much you need, where to find it and who might need to supplement their diet

Overview of magnesium

What is magnesium and what does it do?

is one of the most abundant minerals in your body. It’s needed for hundreds of processes, including:1
  • supporting the nervous system
  • breaking down food into nutrients
  • muscle function, including heart muscle
  • maintaining electrolyte balance
  • healthy bones and teeth
  • normal cell division2
A magnesium deficiency is rare, but symptoms include loss of appetite, nausea and fatigue.3 Magnesium-rich foods include green leafy veg and wholemeal bread, so most people get all they need from their diet.4 It’s also available as tablets, capsules or a spray, or as part of a multi-vitamin.

Is magnesium a metal?

Yes, magnesium is a metal! Weird, right? The same metal that’s used to make heat-resistant bricks for fireplaces and furnaces helps our bodies to run normally. Magnesium is a trace metal, which means that although it is important for overall health, we don’t need large amounts of it.

Functions of magnesium

What does magnesium do in the body?

Magnesium benefits many enzymes in the body, some of which are responsible for converting the food you eat into energy.

What are the benefits of magnesium?

Helps turns the food we eat into energy

The mineral is especially important for breaking protein down into amino acids.5

Because it’s so important for energy release, this makes magnesium critical to many other processes in the body – for example, the nervous system and release of neurotransmitters, or chemical messengers.

Supports muscle function

Magnesium is also needed for muscle contraction and relaxation, including the muscles in your heart. Magnesium works as a natural blocker to calcium – which triggers muscle contractions – helping the cells relax.7

Helps keep our bones strong

Magnesium also plays a key role in the structural development of our bones. A 2014 study by the American Journal of Clinical Nutrition Scientists reported that a magnesium deficiency is associated with low bone density.8 This can put you at risk of bone-thinning conditions such as osteoporosis.

Can help reduce blood pressure

Having high blood pressure can put unnecessary stress on your heart and blood pressure, which in turn raises the risk of heart attacks and strokes. Magnesium has been shown to help lower blood pressure and improve blood flow.9

It’s thought that this could be because magnesium helps the body to release a hormone-like compound called prostacyclin. Prostacyclin is known to reduce tension in blood vessel walls.

May help to control blood sugar

We already know magnesium is needed to convert the food we eat into energy, which also gives it an important role in controlling our blood sugar levels.

When we eat carbohydrates like bread, grains and sugar, our pancreas needs to release insulin so our cells can absorb glucose for energy. If we haven’t consumed enough magnesium, our cells can become less effective at using insulin, causing our blood sugar levels to dip.

This can make us feel hungry, tired, shaky, dizzy, weak and nauseous, and can even lead to diabetes if our bodies stop producing insulin.

Can support hormonal function

As magnesium is needed for over 400 essential functions in our body, it should come as no surprise that it may have an impact on our hormones. Here’s the possible benefits it could have:

  • Combats pre-menstrual syndrome symptoms (PMS) – temporary low mood, anxiety and water retention are some of the most common symptoms of PMS. One study found that a supplement of magnesium and vitamin B6 significantly improved these symptoms compared to a placebo.10

  • Balances mood - Magnesium deficiency has been linked to depression. It is thought that magnesium plays a part in maintaining neurotransmitters in our brain that help regular our moods.

  • Regulates our body clock – Keeping a healthy circadian rhythm (physical, mental and behavioural changes in a daily cycle) is important. Magnesium has been found to control how cells ‘keep time’ and cope with the natural day and night cycle of life. Researchers have found that concentrations of magnesium in all types of cells rose and fell in a 24-hour cycle – impacting the cells’ internal clocks.11

  • Magnesium to help sleep quality in older adults - A lot of elderly people suffer from insomnia (not being able to sleep). Sleep – and lack of it - is very connected to our hormones. A study on supplementation of magnesium and how it effected insomnia in older adults found that magnesium appeared to improve symptoms.12
Read more about how magnesium benefits your hormones here

How much magnesium do I need?

Women need 270mg a day, while breast-feeding women need an extra 50mg a day. Men need 300mg a day.13 14 That’s about the amount found in 30g of pumpkin seeds, an avocado, a banana or an 80g portion of spinach.

How much magnesium do children need?

  • 1-3 years – 85mg a day
  • 4-6 years – 120mg a day
  • 7-10 years – 200mg a day
  • 11-14 years – 280mg a day
  • 15-18 years – 300mg a day11

What foods have magnesium? And, which foods are the best sources of magnesium?

Plants are the best food sources of magnesium. Some common foods rich in magnesium include: 15,16

Vegan sources of magnesium

Seeds and nuts

  • Brazil nuts – approx. 376 mg per 100g

  • Pumpkin seeds – approx. 262 mg per 100g

  • Almonds – approx. 76.5 mg per 23 nuts

  • Cashews, dry roasted – approx. 73.7 mg per 18 nuts

  • Peanuts – approx. 50mg per 28 nuts


  • Spinach, cooked – approx. 87mg per 100g

  • Avocado – approx. 58mg per 1 medium

  • Plantain, raw – approx. 109g per 1 medium

  • Baked potato – approx. 39mg per 1 medium

  • Kale – approx. 33mg per 100g

  • Okra, raw – approx. 57mg per 100g

  • Broccoli, raw – approx. 21mg per 100g


  • Dried figs – approx. 68mg per 100g

  • Dried prunes – approx. 44mg per 100g

  • Magnesium in a banana 32mg per 100g


  • Edamame beans, cooked – approx. 64mg per 100g

  • Black beans – approx. 171mg per 100g

  • Lentils – approx. 36mg per 100g


  • Bulgur wheat – approx. 32mg per 100g

  • Brown / wild rice – approx. 37mg per 100g

  • Quinoa, cooked – approx. 64mg per 100g


  • Soya milk – approx. 36mg per 250ml

  • Soya mock meats

  • Tofu – approx. 60mg per 100g

Non-vegan sources of magnesium

  • Mackerel, cooked – approx. 97mg per 100g

  • Tuna, cooked – approx. 64mg per 100g

  • Scallops, cooked – approx. 44mg per 100g

  • Salmon, cooked – approx. 37mg per 100g

  • Oysters, steamed – approx. 36mg per 100g

Surprising sources of magnesium

  • Dark chocolate (70-85% cacao) – approx. 228mg in 100g bar

Magnesium deficiency

What are the symptoms of a magnesium deficiency?

Magnesium deficiency is rare as it is found in so many of the foods we eat every day. Our kidneys also help to regulate magnesium levels in the body by limiting the amount we lose when we urinate.17 Early signs and symptoms of magnesium deficiency include:18
  • appetite loss
  • nausea
  • fatigue
  • weakness
  • diarrhoea
Symptoms of a moderate deficiency include numbness, tingling and an abnormal heart rhythym.19

Who is most at risk of magnesium deficiency?

About 40% of girls aged 11 to 18 years have low magnesium levels, according to the 2011 National Diet and Nutrition Survey.20 People who abuse alcohol, older adults and people with type 2 diabetes could be more susceptible to magnesium deficiency as they may not absorb enough of the nutrient.21

What happens if I consume too much magnesium?

Taking high doses of magnesium of more than 400mg a day for short periods can lead to diarrhoea, according to the NHS.22  This means you should be careful about how much magnesium you consume from supplements.

Magnesium supplements

When should I take a magnesium supplement?

If you eat a balanced diet with a wide range of foods every day, you should get all the magnesium you need. However, you can take magnesium as a supplement if you think you’re lacking or deficient.

Should children take magnesium supplements?

Children should be able to get all the magnesium they need from their diets.

Should women take a magnesium supplement during pregnancy?

You can get all the magnesium you need from your diet during pregnancy. However, a 2017 report in Advanced Biomedical Research found that many pregnant women are deficient in this mineral. Ask your GP for a blood test if you think you may have low levels of magnesium.23

What are the potential benefits of magnesium supplements?

As magnesium is important for a healthy nervous system, low levels may be linked to the development of migraine. A 2012 study in Journal of Neural Transmission found that up to half of people with migraine were deficient in the mineral.24 With 60% of magnesium stored in our bones, research also shows that a diet containing enough magnesium can help lower the risk of developing osteoporosis. It’s thought magnesium deficiency impacts bone cells and crystal formation, and increases inflammation.25

Which magnesium supplement is best for me?

  • Magnesium tablets: Quick, easy and usually the most cost effective, taking magnesium tablets is the most common way to supplement magnesium.

  • Magnesium spray: Using a spray is a great alternative to tablets if you struggle to swallow them or just straight up say no to popping the pills! A lot of people use magnesium spray for sleep enhancement as it tends to be absorbed faster than a lot of other supplements so you can have a spritz or two before bed to see if it works for you.

  • Magnesium drinks: Another way to get your magnesium is by drinking it. The magnesium has already been absorbed into the liquid, so it bypasses the digestive system and goes straight to work in your bloodstream.

What about magnesium bath salts?

Magnesium flakes (magnesium chloride) and Epsom salts (magnesium sulphate) are known bath-time favourites, claiming to help reduce muscle fatigue and help you relax.

It is claimed that magnesium flakes elevate cellular magnesium levels when exposed to our skin. This allows magnesium compounds to break bonds and travel through the pores into the dermal layers and ultimately the bloodstream.26

When is the best time to take magnesium supplements?

It doesn’t really matter what time you take magnesium supplements, unless you plan on using them to help you sleep. Take magnesium 1-2 hours before going to bed if you want to use it as a sleep aid.

However, make sure you take magnesium supplements with a meal. Due to its laxative effects, you should avoid taking it on an empty stomach or in-between meals or you may have some tummy troubles.

Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.

Last updated: 4 August 2020