Magnesium is the fourth most abundant mineral in the human body, serving as an essential cofactor in over 300 enzymatic reactions. This vital nutrient plays fundamental roles in energy production, muscle and nerve function, bone health, and cardiovascular regulation. With approximately 25 grams stored throughout the body—primarily in bone and soft tissues—magnesium must be obtained entirely through diet or supplementation. Understanding what magnesium does for the body helps explain why adequate intake is crucial for maintaining normal physiological function and why deficiency can manifest in diverse ways across multiple organ systems.

What Does Magnesium Do for the Body?

Magnesium is the fourth most abundant mineral in the human body and serves as an essential cofactor in over 300 enzymatic reactions. This vital nutrient plays a fundamental role in maintaining normal physiological function across multiple organ systems, from energy production at the cellular level to the regulation of muscle contraction and nerve transmission.

The body contains approximately 25 grams of magnesium, with roughly 60% stored in bone tissue, 39% in soft tissues and muscles, and only 1% in blood serum. This distribution can vary by age, sex and bone health. Despite the small circulating amount, serum magnesium levels are tightly regulated because even minor fluctuations can significantly impact cellular function. Within physiological ranges, magnesium helps regulate calcium balance, which is crucial for proper muscle function, including the heart muscle.

Unlike some nutrients that the body can synthesise, magnesium must be obtained entirely through dietary sources or supplementation. The mineral is absorbed primarily in the small intestine, with absorption rates varying between 30% and 50% depending on dietary intake and individual physiological factors. Once absorbed, magnesium is distributed throughout the body where it participates in critical processes including DNA and RNA synthesis, protein formation, and the maintenance of electrical gradients across cell membranes. Understanding magnesium's multifaceted roles helps explain why adequate intake is essential for overall health and why deficiency can manifest in diverse and sometimes subtle ways.

Essential Functions of Magnesium in Human Health

Energy Production and Metabolism

Magnesium is indispensable for adenosine triphosphate (ATP) production, the primary energy currency of cells. The mineral forms a complex with ATP, and this magnesium-ATP complex is the biologically active form that enzymes recognise and utilise. Without adequate magnesium, cellular energy production becomes compromised, potentially leading to fatigue and reduced physical performance. Magnesium also activates enzymes involved in carbohydrate metabolism and influences insulin secretion and action, contributing to glucose homeostasis.

Cardiovascular and Muscle Function

The heart muscle requires magnesium for proper electrical conduction and rhythmic contraction. Magnesium helps maintain normal heart rhythm by regulating the movement of calcium, sodium, and potassium ions across cardiac cell membranes. In skeletal muscle, magnesium acts as a natural muscle relaxant by competing with calcium for binding sites. This calcium-magnesium balance is essential for normal muscle contraction and relaxation cycles. While inadequate magnesium can contribute to muscle cramps and spasms, it's important to note that magnesium supplements are not routinely recommended for idiopathic leg cramps in UK clinical practice unless there is evidence of deficiency.

Nervous System and Bone Health

Magnesium modulates neurotransmitter release and neuronal excitability, playing a protective role in the nervous system. It acts as a natural antagonist at N-methyl-D-aspartate (NMDA) receptors. While some research suggests magnesium may influence mood and cognitive function, the evidence for supplementation in these areas remains limited and of low certainty. Approximately 60% of the body's magnesium resides in bone tissue, where it contributes to bone structural development and influences the activity of osteoblasts and osteoclasts—the cells responsible for bone formation and resorption. Magnesium also affects parathyroid hormone secretion and vitamin D metabolism, both crucial for calcium homeostasis and bone mineralisation.

Signs Your Body May Need More Magnesium

Early and Common Symptoms

Magnesium deficiency, clinically termed hypomagnesaemia, often develops gradually and may initially present with non-specific symptoms that are easily overlooked. Early signs include persistent fatigue, general weakness, and loss of appetite. Many individuals experience muscle cramps, particularly in the legs and feet, along with muscle twitches or fasciculations. These muscular symptoms occur because magnesium deficiency increases neuromuscular excitability. Some people report experiencing eyelid twitching, which, whilst often benign, can indicate suboptimal magnesium status when persistent.

Neurological and Psychological Manifestations

As magnesium plays a crucial role in nervous system function, deficiency can manifest with neurological symptoms including numbness, tingling sensations (paraesthesia), and in some cases, mood changes. There is emerging evidence suggesting a relationship between low magnesium levels and increased anxiety, though there is no established causal link between magnesium deficiency and anxiety disorders. Some individuals may experience difficulty concentrating or mental fog, though these symptoms are non-specific and can result from numerous conditions.

When to Seek Medical Advice

Severe magnesium deficiency, though uncommon in healthy individuals consuming a balanced diet, can lead to more serious complications including cardiac arrhythmias, severe muscle spasms (tetany), seizures, and personality changes. Deficiency is often defined as serum magnesium below 0.7 mmol/L and may be accompanied by low calcium and potassium levels.

Call 999 or go to A&E immediately if you experience:

• Chest pain or severe palpitations, especially with dizziness or fainting

• Seizures

• Acute confusion

Contact your GP if you experience:

• Persistent muscle cramps or spasms that don't improve with hydration

• Unexplained fatigue lasting more than two weeks

• Irregular heartbeat or mild palpitations

• Numbness or tingling that persists or worsens

• Any concerning symptoms, particularly if you have conditions affecting absorption (such as Crohn's disease) or take medications that may deplete magnesium (including certain diuretics, proton pump inhibitors, some chemotherapy drugs or calcineurin inhibitors)

If you're unsure about the urgency of your symptoms, contact NHS 111 for advice. Your GP can arrange a blood test to assess your magnesium levels, though it's important to note that serum magnesium may not always reflect total body stores, as most magnesium resides within cells and bone.

How to Get Enough Magnesium Through Diet

Recommended Intake and Dietary Sources

The NHS recommends a daily magnesium intake of 300 mg for men (aged 19–64 years) and 270 mg for women in the same age group. Fortunately, magnesium is widely distributed in both plant and animal foods, making it achievable to meet requirements through a varied, balanced diet. Excellent dietary sources include:

• Green leafy vegetables: Spinach, kale, and Swiss chard (magnesium is part of the chlorophyll molecule)

• Nuts and seeds: Almonds, cashews, pumpkin seeds, and sunflower seeds

• Whole grains: Brown rice, wholemeal bread, quinoa, and oats

• Legumes: Black beans, chickpeas, and lentils

• Fish: Mackerel, salmon, and halibut

• Dark chocolate: Contains significant magnesium (choose varieties with 70% cocoa or higher)

• Avocados: Provide magnesium along with healthy fats

Optimising Absorption and Practical Tips

Magnesium absorption can be influenced by several dietary factors. Phytates, found in whole grains and legumes, can bind magnesium and reduce absorption, though soaking, sprouting, or fermenting these foods can help mitigate this effect. Magnesium is required for vitamin D activation and metabolism. Excessive alcohol consumption can increase urinary magnesium excretion and impair absorption, so moderation is advisable.

For most people, obtaining magnesium through food is preferable to supplementation, as whole foods provide additional nutrients and fibre. However, certain groups may be at higher risk of deficiency, including older adults (due to reduced absorption and increased losses), individuals with gastrointestinal conditions (such as coeliac disease or inflammatory bowel disease), people with type 2 diabetes, and those taking certain medications long-term.

If you're considering magnesium supplements, consult your GP or a registered dietitian first. According to NHS guidance, supplemental magnesium up to 400 mg per day is unlikely to cause harm in most adults. Higher doses may cause diarrhoea and, in rare cases, more serious adverse effects. People with kidney disease should seek medical advice before taking magnesium supplements.

Important medicine interactions: Separate magnesium supplements from tetracycline antibiotics, quinolone antibiotics, bisphosphonates and levothyroxine by at least 2-3 hours, as magnesium can reduce their absorption.

If you experience any side effects from magnesium supplements, report them through the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions