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Magnesium (Serum)

What is Magnesium?

Magnesium is an abundant mineral which the body needs for many functions, including energy production, nerve function and muscle contraction. As the body can’t make it, we must acquire magnesium through the diet where it is absorbed via the small intestine. Approximately 50% of the body’s total magnesium is joined to calcium and phosphorus to make bone.[1]

Why take a Magnesium blood test?

A magnesium blood test measures the amount of magnesium present in the blood. There is usually only a small amount, around 1%, of the body’s total magnesium in the blood. Magnesium levels may fluctuate if you have a condition affecting your kidney or intestine function.[2]

Magnesium levels can interfere with calcium level regulation and low magnesium levels can make it harder for low calcium levels to increase.

You can test your magnesium levels by purchasing a simple at-home finger prick test kit which is then analysed at an accredited lab. Forth offers a number of blood tests which include magnesium such as our Nutri-check test and Menopause Health blood test. A magnesium blood test is also available in some of our bigger blood test profiles such as Vitality which tests over 30 biomarkers integral to good health.

What function does Magnesium have in the body?

Magnesium is a co-factor in over 300 biochemical reactions including protein synthesis, muscle and nerve transmission and blood pressure regulation. So, it is important we acquire enough magnesium in our diet to fulfil the needs of the body. Magnesium is also vital for the structural function of proteins, mitochondria and nucleic acids.[3]

Magnesium stabilises many enzymes, particularly those involved in energy production. Energy is essential for many of the body’s functions such as muscle contraction, production of fats, proteins and nucleic acids. For example, during muscle contraction magnesium is involved in the reuptake of calcium allowing contraction to take place.[4] Magnesium also has an important role in bone mineralisation.[5]

How do changes in Magnesium affect health and wellbeing?

Magnesium has many functions within the body and so fluctuations in the levels of the mineral can affect our health and wellbeing. For example, low magnesium (hypomagnesemia) is associated with neurological issues like migraines, depression and epilepsy. It is uncommon for magnesium deficiency to occur in otherwise healthy individuals because the kidneys regulate its excretion.[6] However, there are certain health conditions which can cause excessive magnesium losses or cause habitually low intakes such as chronic alcoholism and taking certain medications. If your magnesium intake is routinely low, then this can cause changes in biochemical pathways, increasing the risk of illnesses, such:

  • high blood pressure
  • cardiovascular disease
  • type ii diabetes
  • osteoporosis
  • migraine headaches

Equally, too much magnesium (hypermagnesemia) can make you feel quite unwell, inducing symptoms such as diarrhoea, abdominal cramping and nausea. Diarrhoea and the laxative effect of magnesium are caused by the osmotic activity in the intestine by unabsorbed salts and the promotion of gastric motility.

If you are worried about your magnesium level or just want to check where you fall on the range, you can test your magnesium level with a simple at-home blood test.

What can cause Magnesium to change?

Usually, high levels of magnesium in the body are caused by dietary supplements or medication containing magnesium and rarely through dietary intake.

Magnesium deficiency, on the other hand, is common and is on the rise in the western world. Often magnesium deficiency occurs alongside other electrolyte deficiencies, particularly calcium and potassium. Magnesium is essential for the regulation of calcium and, therefore, can exacerbate calcium deficiency. There are several factors which can cause decreased magnesium levels. They are:

  • Low dietary intake
  • Vomiting and diarrhoea
  • Chronic alcoholism
  • Genetics

Approximately one-quarter of plasma magnesium is bound to albumin. Therefore, if albumin levels are high or low, this can affect magnesium levels, too.[7]


What are the most common symptoms of Magnesium deficiency?

The most common symptoms associated with magnesium deficiency are:

  • Loss of appetite
  • Nausea
  • Vomiting
  • Weakness
  • Fatigue
  • Muscle contractions and cramps
  • Numbness
  • Tingling

Although rare, the symptoms of excess magnesium are:

  • Diarrhoea
  • Nausea
  • Stomach cramps

How to keep Magnesium in the healthy range

Because magnesium can affect other mineral levels in the body, it is essential that we get enough of it in our diet. By eating a healthy, balanced diet we should be able to acquire all the magnesium the body needs.

You should aim to consume a variety of fruit, vegetables, whole grains, low-fat dairy products and oils. Good sources of magnesium, include:

  • whole grains
  • dark, green leafy vegetables
  • low-fat milk and yoghurt
  • breakfast cereals fortified with magnesium
  • dried beans and legumes
    • baked beans
    • soybeans
  • peanuts
  • almonds
  • cashews

Try to keep your alcohol consumption within a healthy range. The government guidelines state we should all consume no more than 14 units of alcohol per week and we should spread this out over the week rather than binge in one go. Staying hydrated is also key, particularly as the kidneys control the excretion of magnesium. You should aim to drink around two litres of water per day but this can vary according to physical activity and climate.

Magnesium (Serum) Tests

All these tests include Magnesium (Serum). Select the test that suits your personal needs.

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Magnesium Blood Test

Keep track of your magnesium levels with our at-home blood test.

magnesium, energy, bone, heart, nerve, bone health, heart health
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Ultimate Health Check

Advanced health test that checks heart, liver, kidney, thyroid, and muscle function, nutrition, immune health, hormones and more.

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Nutricheck – Vitamin Deficiency Blood Test

Looking to improve your diet and get a better understanding of your overall health and nutrition? Nutricheck home blood test can help.

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[1] Lab Tests Online UK. (2018). Magnesium. Available at:

[2] NHS. (2018). Magnesium Test. Available at:

[3] Grӧber, U et al. (2015). Magnesium in Prevention and Therapy. Nutrients: 7, pp 8199-8226.

[4] Jahnen-Dechent, W and Ketteler, M. (2012). Magnesium Basics. Clin Kidney J: 5(suppl 1), pp i3-i14.

[5] Alawi, A, M, Al et al. (2018). Magnesium and Human Health: Perspectives and Research Directions. International Journal of Endocrinology.

[6] National Institutes of Health Office of Dietary Supplements. (2018). Magnesium. Available at:

[7] NHS Dorset Clinical Commissioning Group. (2017). The Management of Hypomagnesaemia in Primary Care. Available at:

Medically reviewed

This information has been medically reviewed by Dr Nicola Keay.

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas’ Hospital.

Nicky Keay
Dr Nicola Keay

BA, MA (Cantab), MB, BChir, MRCP.​

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