Magnesium is a vital mineral supporting over 300 enzymatic reactions in the body, from energy production to bone health and muscle function. In the UK, the recommended daily intake varies by age and sex, with adult men requiring 300 mg and adult women 270 mg per day. Most people can meet these needs through a balanced diet rich in green leafy vegetables, nuts, seeds, and whole grains. Understanding your magnesium requirements and recognising signs of deficiency can help you maintain optimal health and prevent complications.

What Is the Recommended Daily Dose of Magnesium in the UK?

The recommended daily intake of magnesium in the United Kingdom varies according to age and sex, as established by the Department of Health. For adult men aged 19 and over, the Reference Nutrient Intake (RNI) is 300 mg per day. Adult women require slightly less, with an RNI of 270 mg per day. These values represent the amount expected to meet the needs of approximately 97.5% of the healthy population.

For children and adolescents, requirements increase progressively with age:

• 0–3 months: 55 mg daily

• 4–6 months: 60 mg daily

• 7–9 months: 75 mg daily

• 10–12 months: 80 mg daily

• 1–3 years: 85 mg daily

• 4–6 years: 120 mg daily

• 7–10 years: 200 mg daily

• 11–14 years: 280 mg for both boys and girls

• 15–18 years: 300 mg for both boys and girls

Pregnant and breastfeeding women do not require additional magnesium beyond the standard adult female RNI of 270 mg per day, according to UK guidance. This differs from some other nutrients where supplementation during pregnancy is routinely advised. However, individual circumstances may warrant different recommendations, and women should discuss their specific needs with their GP or midwife.

It is worth noting that these figures represent the recommended intake for healthy individuals. Some people with certain medical conditions, those taking specific medications, or individuals with increased physiological demands may require different amounts under medical supervision.

Why Magnesium Is Essential for Your Health

Magnesium is the fourth most abundant mineral in the human body and participates in over 300 enzymatic reactions, making it indispensable for normal physiological function. Approximately 60% of the body's magnesium is stored in bone tissue, where it contributes to structural development and serves as a reservoir for maintaining serum levels. The remainder is distributed in soft tissues, muscles, and bodily fluids.

Key physiological roles include:

• Energy metabolism: Magnesium is a cofactor for adenosine triphosphate (ATP) synthesis, the primary energy currency of cells. It facilitates the conversion of food into usable energy and is essential for mitochondrial function.

• Protein synthesis and DNA/RNA production: Magnesium is required for the synthesis of nucleic acids and proteins, supporting cell growth, repair, and genetic expression.

• Neuromuscular function: The mineral regulates nerve impulse transmission and muscle contraction, including cardiac muscle. It acts as a natural calcium antagonist, helping to maintain normal heart rhythm and vascular tone.

• Bone health: Magnesium influences bone mineral density by affecting osteoblast and osteoclast activity. It also regulates parathyroid hormone and vitamin D metabolism, both critical for calcium homeostasis.

• Glucose regulation: Magnesium plays a supportive role in insulin secretion and glucose metabolism. Research suggests associations between magnesium status and glucose handling.

• Blood pressure regulation: Through its effects on vascular smooth muscle and endothelial function, magnesium may contribute to cardiovascular health.

Insufficient magnesium can affect these processes, potentially contributing to various health concerns including muscle cramps, fatigue, and metabolic disturbances.

How to Know If You Need More Magnesium

Magnesium deficiency (hypomagnesaemia) is relatively uncommon in healthy individuals consuming a balanced diet, as the mineral is widely distributed in foods. However, certain populations are at increased risk, and recognising the signs of inadequate intake is important for timely intervention.

Early symptoms of magnesium insufficiency may be subtle and non-specific, including:

• Muscle cramps, twitches, or spasms, particularly in the legs

• Persistent fatigue or weakness

• Loss of appetite or nausea

• Numbness or tingling sensations

More pronounced deficiency can lead to cardiac arrhythmias, personality changes, seizures, and disturbances in calcium and potassium balance. However, these severe manifestations are rare and typically occur only in the context of significant underlying disease.

Risk factors for magnesium deficiency include:

• Gastrointestinal disorders: Conditions such as Crohn's disease, coeliac disease, or chronic diarrhoea impair magnesium absorption in the small intestine.

• Type 2 diabetes: Poor glycaemic control can increase urinary magnesium loss due to glycosuria and altered renal handling.

• Chronic alcohol use: Alcohol increases renal magnesium excretion and reduces dietary intake and absorption.

• Medications: Proton pump inhibitors (PPIs), loop and thiazide diuretics, aminoglycosides, and amphotericin B can reduce magnesium levels.

• Older adults: Age-related changes in absorption, dietary intake, and medication use increase vulnerability.

If you experience persistent symptoms or have risk factors, consult your GP. Diagnosis typically involves a serum magnesium blood test (with levels below 0.7 mmol/L indicating deficiency), though this may not always reflect total body stores. Your doctor may recommend additional tests such as calcium and potassium levels.

Seek emergency care (call 999 or go to A&E) if you experience new palpitations, seizures, or fainting, which could indicate severe deficiency requiring urgent treatment.

Food Sources and Supplements: Meeting Your Daily Magnesium Needs

The most effective and safest way to meet your daily magnesium requirements is through a varied, balanced diet. Magnesium is present in numerous foods, particularly those of plant origin, making dietary sufficiency achievable for most people.

Excellent food 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, oats, and quinoa

• Legumes: Black beans, chickpeas, lentils, and kidney beans

• Fish: Mackerel, salmon, and halibut

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

• Avocados: Provide magnesium alongside healthy fats

• Bananas: A convenient source, though more modest in content

Food preparation methods can affect magnesium content. Boiling vegetables may leach some magnesium into cooking water, so steaming or consuming raw where appropriate may preserve more of the mineral.

Magnesium supplements are available in various forms, including magnesium oxide, citrate, glycinate, and chloride. Some forms, such as citrate and glycinate, may be more soluble than oxide, though individual tolerance varies. Supplements are typically unnecessary for healthy individuals eating a balanced diet, but may be recommended for those with documented deficiency or specific medical conditions.

If considering supplementation, consult your GP or a registered dietitian first. They can assess whether supplementation is appropriate, recommend the correct dose and formulation, and monitor for potential interactions with medications.

Important medication interactions: Separate magnesium supplements from these medicines by at least 2-4 hours:

• Levothyroxine (thyroid medication)

• Tetracycline and quinolone antibiotics (e.g., doxycycline, ciprofloxacin)

• Bisphosphonates (e.g., alendronate for osteoporosis)

The NHS does not routinely recommend magnesium supplements for the general population, and self-prescribing high doses may cause adverse effects.

Risks of Taking Too Much Magnesium

Whilst magnesium toxicity (hypermagnesaemia) from dietary sources alone is extremely rare in individuals with normal kidney function, excessive supplementation can lead to adverse effects. The kidneys efficiently excrete excess magnesium under normal circumstances, but this protective mechanism can be overwhelmed by high supplement doses or impaired in those with renal disease.

The UK Expert Group on Vitamins and Minerals has established a Guidance Level for magnesium from supplements at 400 mg per day for adults, in addition to dietary intake. This guidance specifically applies to supplemental magnesium, not total intake from all sources, as dietary magnesium does not typically cause toxicity.

Common side effects of magnesium supplementation include:

• Diarrhoea (magnesium has an osmotic laxative effect)

• Abdominal cramping and bloating

• Nausea and vomiting

These gastrointestinal symptoms can occur even at doses below 400 mg, particularly with certain forms like magnesium oxide, and typically resolve when intake is reduced.

Severe magnesium toxicity is uncommon but can occur with very high doses (typically several grams) or in individuals with impaired renal function. Symptoms may include:

• Hypotension (low blood pressure)

• Cardiac arrhythmias or heart block

• Respiratory depression

• Muscle weakness or paralysis

• Confusion or altered mental state

Particular caution is warranted in individuals with chronic kidney disease, as reduced renal clearance significantly increases toxicity risk. Those taking certain medications should seek medical advice before supplementing, as magnesium can interact with:

• Antibiotics (tetracyclines, quinolones)

• Bisphosphonates for osteoporosis

• Levothyroxine for thyroid conditions

• Some blood pressure and heart medications

If you experience mild symptoms suggestive of magnesium excess, discontinue supplementation and contact your GP. For severe symptoms such as significant weakness, collapse, or irregular heartbeat, call 999 or go to A&E immediately.

If you suspect side effects from a magnesium-containing medicine, you can report this through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Frequently Asked Questions