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Magnesium (Serum)

Magnesium is present in every organ and involved in more than 300 biochemical reactions, cementing its importance in human health. Yet, it’s often an overlooked macronutrient. Let’s explore why magnesium is so fundamental for health and wellbeing.

Author: Written by Leanne Edermaniger

May 20, 2024

Reviewed by: Dr Thom Phillips

In this article:

What is Magnesium (Serum)?

Magnesium is a micronutrient. Micronutrients are vitamins and minerals needed in small quantities to support the body’s normal function.

Magnesium is important for regular physiological functions, including:

  • Bone health
  • Energy metabolism
  • Muscle function
  • Nerve function
  • Blood pressure regulation
  • Mood
  • Blood sugar regulation and insulin activity[1]

Magnesium and calcium work closely together in the body. Magnesium is critical for calcium absorption and low levels are linked to low bone mineral density in men and women[2].

The heart and circulatory system need magnesium for regulating ion transporters involved in the heart muscle contraction to ensure blood is pumped efficiently around the body and for vascular tone. Magnesium may have a protective benefit against the development of cardiovascular disease[3].

Magnesium is an essential micronutrient. If you don’t get enough in your diet over a sustained period, you could be at an increased risk of health issues.

The NHS states that men need 300 mg daily and women require a 270 mg daily magnesium intake[4]. Most people should get their recommended daily magnesium intake simply by eating a healthy and varied diet.

What are Normal Magnesium Serum Levels?

A healthy range for magnesium is 0.7 to 1.0 mmol/L.

At Forth, our customer data shows that the average magnesium level in 2024 is 0.93 mmol/L.

The average magnesium level for each sex is:

  • 0.92 mmol/L for women
  • 0.94 mmol/L for men

Are high magnesium levels dangerous/bad?

High levels of magnesium in the blood, also known as hypermagnesemia, can be dangerous, increasing the risk of heart problems, neurological dysfunction, and shock.

However, hypermagnesemia is very rare. The most common causes are kidney dysfunction and consuming or supplementing too much magnesium[5].

What Causes Low Magnesium Levels?

Magnesium deficiency, hypomagnesemia, is a condition characterised by having low magnesium levels in the blood.

There are several reasons why magnesium levels may be below the normal range, including:

  • Inadequate dietary intake
  • Gastrointestinal issues e.g., chronic diarrhoea, reduced absorption, Crohn’s disease
  • Medicines e.g., diuretics to make you pee more
  • Kidney disease or dysfunction
  • Diabetes
  • High alcohol consumption
  • High calcium intake
  • Overactive thyroid[6]

For many people, low magnesium levels are caused by insufficient micronutrients in their diet. So, it is important to incorporate magnesium-rich foods into your daily diet, such as avocados, cashew nuts, almonds, legumes, wholegrains, and spinach.

Symptoms of low magnesium

  • Muscle cramps and weakness
  • Fatigue
  • Tremors
  • Abnormal heart rhythm
  • Feeling sick (nausea)
  • Being sick (vomiting)[7]

It can take months or years for magnesium to fall to noticeably low levels. You may not know you are deficient until you start experiencing these symptoms.

What Causes High Magnesium Levels?

High magnesium levels or hypermagnesemia is a rare condition which results in too much magnesium circulating in the blood.

The most common cause for high magnesium levels is impaired kidney function or kidney failure but it can also be caused by excessive intake.

Taking magnesium-containing laxatives and heartburn medicines increases the risk of hypermagnesemia in some people[8].

Other causes include:

  • Dehydration
  • Underactive thyroid (hypothyroidism)
  • Hyperparathyroidism (overactive parathyroid gland)
  • Addison’s disease
  • Diabetic acidosis[9]

Although high levels are uncommon, hypermagnesemia can be a sign of an underlying health condition, or if you supplement your magnesium intake, it could indicate that you are taking too much.

Symptoms of high magnesium

  • Confusion
  • Sleepiness
  • Headache
  • Constipation
  • Muscle weakness
  • Feeling sick (nausea)
  • Dizziness
  • Blurred vision
  • Low blood pressure8

How To Check Your Magnesium Levels

The most common way to check your magnesium levels is a blood test.

You can conveniently measure your serum magnesium levels with our at-home Magnesium Blood Test kit. You’ll receive everything you need to take a blood sample using a finger prick test kit and return your sample to our lab, to receive your result within 2 working days.

Your magnesium levels are also measured as standard with our at-home:

A blood test can’t quantify total magnesium levels because most of it is stored in the muscles, bones, and soft tissue. Around 1% of the body’s magnesium circulates in the blood. This is called serum magnesium and that’s what we test. Serum magnesium is the most common test for analysing magnesium levels in the body.

How To Increase Your Levels

The human body is not equipped with the tools needed to make magnesium, so it must be acquired in the food you eat. That means you can support or increase your magnesium levels by making some easy lifestyle changes.

The NHS states that men need 300 mg per day and women require a 270 mg daily magnesium intake[10]. Most people should get their recommended daily magnesium intake simply by eating a healthy and varied diet.

Here are a few tips to boost your magnesium levels:

  • Increase your magnesium intake: Magnesium is abundant in many foods, so it is important to incorporate magnesium-rich foods into your diet.
  • Lower alcohol intake: Alcohol interferes with several electrolyte levels but the most common is magnesium. Excessive drinking can cause your magnesium levels to be depleted from your tissues and through increased urine output[11].
  • Reduce your exposure to stress: There is growing evidence to suggest that ongoing stress is a cause of magnesium deficiency and that low magnesium intake makes you more vulnerable to stress, anxiety, and depression[12].
  • Check existing medication: Some medicines are known to lower magnesium levels, such as proton pump inhibitors, prescribed to reduce stomach acid production (omeprazole and lansoprazole), and diuretics that reduce fluid buildup in the body. If you take any medicines, find out if they could lower your magnesium levels and speak to your doctor if you are concerned.
  • Take a supplement: You should be able to get all the magnesium your body needs from your diet, but you might consider magnesium supplements if your levels are low or you have an underlying cause of deficiency. However, if you have an underlying medical condition or are taking any medication, you should first discuss taking magnesium supplements with your doctor.

What foods are high in magnesium?

Good sources of magnesium include:

  • Green, leafy vegetables
  • Nuts
  • Seeds
  • Beans
  • Dark chocolate
  • Avocados
  • Tofu
  • Wholegrains

What drinks are high in magnesium?

  • Mineral water
  • Cocoa
  • Spinach-based smoothies or juice
  • Soy or almond milk

How long does it take to correct magnesium deficiency?

How long it takes to bring your magnesium levels back to within a normal range will depend on how low your levels currently are.

In people with chronic magnesium deficiency, it can take 20 to 40 weeks to reach a normal level using supplements, depending on the prescribed dose[13].

- Health scores calculated


Article references

  1. Swaminathan R. (2003). Magnesium metabolism and its disorders. The Clinical biochemist. Reviews, 24(2), 47–66.

  2. Vatsalya, V. et al. (2020) ‘Lower serum magnesium concentrations are associated with specific heavy drinking markers, pro-inflammatory response and early-stage alcohol-associated liver injury§’, Alcohol and Alcoholism, 55(2), pp. 164–170. doi:10.1093/alcalc/agaa001.

  3. Ismail, A.A., Ismail, Y. and Ismail, A.A. (2017) ‘Chronic magnesium deficiency and human disease; time for reappraisal?’, QJM: An International Journal of Medicine, 111(11), pp. 759–763. doi:10.1093/qjmed/hcx186.

This article was written by Written by Leanne Edermaniger

This information has been medically reviewed by Dr Thom Phillips

Thom works in NHS general practice and has a decade of experience working in both male and female elite sport. He has a background in exercise physiology and has published research into fatigue biomarkers.

Dr Thom Phillips

Dr Thom Phillips

Head of Clinical Services