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A guide to magnesium

Magnesium seems to be the supplement of the moment, but is it all it’s cracked up to be. Dietitian Katrina Pace gives us the lowdown.

Head into any pharmacy and you’ll see row upon row of magnesium supplements. Sold as a way to help you sleep, calm down and relax your muscles, magnesium is being touted as a cure-all for our modern, stressful lives.

Magnesium is needed by our body to produce energy and to help over 600 different enzyme pathways work. Most notably, magnesium plays an important role in glucose metabolism, DNA repair and mood.

How much magnesium do we need?

The recommended dietary intake (RDI) each day for adult men is 420mg and, for women, 320mg. Getting more magnesium than we need from food is fine, as the body can easily get rid of what it doesn’t need. However, that’s not the case with magnesium supplements. For adults, if we take a supplement, it’s recommended we have no more than 350mg a day.

You might be low in magnesium:

  • If you eat a refined, processed Western-style diet
  • As you get older
  • When taking certain antibiotics, antacids and blood pressure medications
  • If you’re a smoker
  • After diarrhoea or vomiting
  • If you have coeliac disease
  • If you have high blood sugar levels.

What’s the evidence?

Magnesium and muscle cramps

While solid evidence is still lacking, research shows magnesium supplements may be beneficial in reducing the severity of muscle cramps. Adding in calcium and potassium to the magnesium may help even more.

Magnesium and migraine

People who get migraines often have lower magnesium levels than others. There is some evidence that improving magnesium levels may help prevent headaches for some migraine sufferers. For more on migraines, head to page 30.

Magnesium and sleep

Trials have shown that taking magnesium may improve sleep time, reduce insomnia and improve melatonin (the hormone required for sleep) production. This may be particularly helpful for older people.

Magnesium and diabetes

People with diabetes often have lower levels of magnesium. Because of its role in glucose metabolism, increased magnesium intake has been found to be beneficial in both types 1 and 2 diabetes and may help improve insulin sensitivity and blood glucose control.

Magnesium in food

Magnesium is found widely in plant foods including seeds, nuts, legumes, cereals and dark leafy greens.

Each of these foods provides 45mg-50mg of magnesium:

  • 1 tablespoon pumpkin seeds
  • 3 Brazil nuts
  • 1 medium baked potato
  • 13 raw almonds
  • 1 cup peas
  • ¾ cup chickpeas
  • 1½ cups steamed silver beet
  • 150g tarakihi

What to look for in magnesium supplements

Supplement doses vary significantly, from 125mg to 500mg. And there are several different types of magnesium. Magnesium oxide is the least readily available to the body. Magnesium chloride, lactate, citrate and aspartate seem to be more easily absorbed. If you’re buying supplements for sleep or muscle relaxation, then check the labels, as there may be other nutrients or herbals added.

Side effects

One of the first side effects of taking too much magnesium from supplements is diarrhoea, which explains why magnesium is used in some remedies for constipation. Other side effects include low blood pressure, muscle weakness, confusion, cardiac arrhythmia and decline in kidney function.
Check with your doctor to make sure a magnesium supplement won’t affect any medications or medical conditions you have.

First published: Sep 2018



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