Magnesium: It's role, sources and cautions

Magnesium is the 4th most abundant mineral in our bodies and has over 300 co-factor roles (co-factors are substances that are required for an enzyme’s activities).  As a cofactor, magnesium enables enzymatic functions, helping stabilise molecules for their biological action.  It is therefore considered a primary 'king' or 'macro' mineral. It is therefore essential, and deficiency could cause ‘malfunction’, as you will read below.

What is Magnesium (Mg), and why is it important?

Magnesium levels are controlled mostly by the kidneys, using urinary excretion. Hypermagnesemia can occur in chronic kidney disease, for example, as the kidneys fail, plasma magnesium levels increase. Therefore, urinary levels will vary dependent on status.

Magnesium can be difficult to monitor, despite its high importance, as it exists in bone (up to 60%) and intracellular states. Bone levels and urinary levels will therefore not necessarily correlate. Evaluation of magnesium levels are best carried out with combined clinical assessment and laboratory testing.

Key roles of magnesium in the body

Co-enzyme factor 

Magnesium assists in many enzymatic activities which allows the synthesis of protein, DNA and RNA and energy production. It is essential or the production of ATP (adenosine triphosphate) which is the body's main source of energy. As an example, low magnesium slows down the production of ATP leading to low energy.

Bone health 

50% - 60% is present in the bones, with the remainder in the soft tissue. A very limited amount exists in the blood serum. It plays a role in regulating calcium and vitamin D levels (essential for bone health) and is linked to improving bone density.

Muscles, nerves and heart health

Muscle and nerve responses are driven partly by magnesium. The heart is a muscle, so it is dependent on the correct balance of magnesium for its function. Also, by regulating calcium absorption Mg in turn regulates heart function/rhythm.

Magnesium supports the ionic movement of minerals (soluble in water) such as calcium, potassium and sodium, policing their levels through cellular osmotic movement. This function reduces inflammation, improves energy, balances insulin levels and reduces blood pressure. Mg deficiency has been found in individuals with congestive heart failure, and correct supervised supplementation could lower the risk of arrhythmia and heart attack mortality.

Blood pressure

A reduction in elevated blood pressure (BP) with a combined mineral approach ie. Reducing intracellular calcium and sodium and increasing intracellular magnesium and potassium, has been found to be successful and in some instances, Mg can improve the effectiveness of some antihypertension medications (although this must be supervised by a health professional).

Vitamin D and calcium

Vitamin D and calcium are regulated by magnesium, so it is essential for strong bones, and preventing osteoporosis. Magnesium acts as a co-factor assisting in the metabolism of Vitamin D. Overdose of Vitamin D could result in elevated calcium, which in turn could cause decreased magnesium. Most adults require 600 iu of vitamin D if supplemented.

Blood sugar control

Glucose metabolism and insulin's role are dependent on magnesium. The World Journal of Diabetes (2015) reported that ‘most, but not all, people with diabetes had low magnesium,’ evidencing its role in diabetes management. Research has also shown that magnesium can improve insulin sensitivity. Again, as a cofactor, magnesium enables glycolysis and the regulation of insulin.

Constipation and digestive health

Magnesium assists in bowel movements and health as well as neutralising stomach acids during stages of digestion. Our microbiome thrive as magnesium reduces gut inflammation and supports the mucosal membranes.

Mental health 

Magnesium assists in nerve responses so plays a role in preventing over-stimulation and contributes to brain health. It regulates a neurotransmitter known as GABA which helps promote sleep and reduce muscular tension. 

Interactions with other minerals and effects

Magnesium and calcium work very closely together, but like any relationship, they can compete for attention. To allow the best absorption and avoid this, it is advisable to take the supplements at either end of the day.

As mentioned above, magnesium is needed for more than just bone and heart health. A vital role is that it acts as a doorman to calcium, stopping it from accumulating in our soft tissues, hardening arteries and organs. When magnesium is low, our bodies are more inclined to deposit calcium into our soft tissues. An example of how this can happen is chronic stress, which can lead to magnesium levels dropping; therefore, lowering stress levels is important to protect magnesium levels. Where stress can lower magnesium, agitation, heart rhythm changes, anxiety, an overactive mind, even cramps and restless legs can then be driven by higher calcium.

Vitamin D also helps our muscles to stay strong, which contributes to better balance and mobility, reducing the risk of fractures and falls. Vitamin D needs magnesium for its activation; therefore, if magnesium is lo,w the effectiveness of Vitamin D may be compromised (even if you have adequate sunlight).

To make the most of magnesium and calcium, supplement half as much magnesium as calcium. Also, take calcium supplements in the morning and magnesium supplements in the evening to avoid conflict.

The nighttime supplementation of magnesium can help with sleep as it stimulates melatonin production in our body and relaxes our muscles. It can also help to reduce our stress levels, contributing to getting a better night's sleep.

Beware the bowels

There can be a temptation to take large amounts of magnesium in the hope of fast-tracking its role. This can trigger diarrhoea, bloating and discomfort. 

Supplementation should be guided as doses can be inappropriate. In most cases, the diet will provide enough, but there are circumstances where this is not the case. Examples of this are:

• fussy eating
• weight loss surgery or injections
• eating Disorders
• anxiety
• certain medications can affect absorption
• inappropriate supplementation

Why is magnesium citrate a popular choice?

Magnesium citrate is magnesium combined with citric acid which forms a salt. This is easily absorbed and gentle on the digestive system if used cautiously. Because of its use for constipation, it has become popular, particularly with the use of weight loss injections, which can cause constipation.

It must be used only occasionally to avoid interrupting the balance of other minerals, leading to health issues, as explained above.

How medications can affect magnesium absorption

Be aware of contraindications to get the best from your medications and supplements. Magnesium is no exception, so a quick reference is listed below:

Antibiotics: Take 2 hrs before or 4 to 6 hrs after any Mg supplement.

Bisphosphonates: Used to help strengthen bones and reduce fracture risk. Mg supplements can reduce the absorption of these medications, lowering their effectiveness.

To reduce this risk, take Mg 2 hrs before or after medicating.

Blood pressure medications: Specifically, calcium channel blockers (amlodipine, verapamil, diltiazem) relax blood vessels, so Mg in combination and lower blood pressure further, causing a risk of collapse, falls, dizziness, and confusion. BP should be monitored carefully with a health care professional.

Sulfonylureas (glimepiride, glyburide, glipizide): A group of medications used to assist in the control of blood sugar levels. Mg can increase their absorption, potentially leading to low blood sugar levels.

Also, some diabetes medications mimic insulin which can lead to Mg leaving the cells and levels dropping. Over a period this drop in Mg will lead to other health problems as mentioned above, so it is important to seek advice when thinking of supplementation.

Proton pump inhibitors (PPIs): These medications are used for acid reflux and can be purchased off the shelf in some cases. There is a real danger of overdose, which can lead to digestive malabsorption. The PPI inhibits magnesium absorption, and symptoms could be fatigue, irregular heartbeat, tremor, anxiety and muscle spasms.

Diuretics or water pills: These medications assist in the removal of excess fluid in the body, but in doing so, they also cause magnesium to be lost through urinary excretion. Some also control potassium levels, which in turn will affect magnesium balance.

Please note that combined medications, so as antacids, diuretics and laxatives have the potential for magnesium deficiency, so serum levels should be monitored.

What foods contain magnesium?

• almonds (roasted): 1 ounce (oz) = 80 mg
• cashews (roasted): 1 oz = 72 mg
• flaxseed (whole): 1 tablespoon = 40 mg
• peanuts (dry roasted): 1 oz = 49 mg
• pumpkin seeds (hulled, roasted): 1 oz = 150 mg
• chia seeds: 1 oz = 111 mg
• black beans (boiled): 1/2 cup = 60 mg
• edamame (cooked, prepared): 1/2 cup = 50 mg
• lima beans (cooked): 1/2 cup = 40 mg
• quinoa (cooked): 1/2 cup = 60 mg
• shredded wheat (plain, unfrosted): 1 cup = 56 mg
• milk (non-fat): 1 cup = 24 to 27 mg
• yoghurt (plain, low fat): 8 oz = 42 mg
• spinach (cooked): 1/2 cup = 78 mg
• swiss chard (cooked): 1/2 cup = 75 mg
• collard greens: 1/2 cup = 25 mg
• kale: 1 cup = 23 mg
• avocados: one whole avocado = 58 mg
• bananas: one medium banana = 32 mg
• papaya: one small papaya = 33 mg
• blackberries: 1 cup = 29 mg
• green peas: 1/2 cup = 31 mg
• sweet corn: 1/2 cup = 27 mg
• potatoes (one medium potato with skin):  48 mg
• tofu: 35 mg per 100g.

Please note: The above quantities are approximate.

Take-home summary

• A balanced diet of fresh whole foods should provide the minerals required for optimal health.
• Magnesium is a ‘king’ mineral with many key functions.
• Certain medications could contribute to magnesium deficiency, so always check with your health care professional and consider blood tests to monitor serum levels.
• Supplementation should be managed with approval of your health care professional (GP, Consultant, Nutritionist or Dietitian) and administered so there are no contraindications or potential for malabsorption or imbalance created with other minerals and vitamins.