Magnesium is a vital mineral supporting over 300 enzymatic reactions in the body, from energy production to heart rhythm regulation. Understanding the recommended dose of magnesium daily helps ensure you meet your nutritional needs without risking deficiency or excess. In the UK, the Reference Nutrient Intake (RNI) is 300 mg per day for adult men and 270 mg per day for adult women. Most people can achieve adequate intake through a balanced diet rich in green leafy vegetables, nuts, seeds, and whole grains. This article explains UK guidance on magnesium requirements, signs of deficiency, dietary sources, and when supplementation may be appropriate.

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 and Social Care. 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 considered sufficient to meet the needs of approximately 97.5% of the healthy population.

For children and adolescents, requirements increase progressively with age:

• Infants 0–3 months: 55 mg daily

• Infants 4–6 months: 60 mg daily

• Infants 7–12 months: 75 mg daily

• Children 1–3 years: 85 mg daily

• Children 4–6 years: 120 mg daily

• Children 7–10 years: 200 mg daily

• Boys 11–14 years: 280 mg daily

• Girls 11–14 years: 280 mg daily

• Boys 15–18 years: 300 mg daily

• Girls 15–18 years: 300 mg daily

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's worth noting that nutrition labels on supplements often use a Nutrient Reference Value (NRV) of 375 mg per day for adults, which differs from the UK RNIs. When assessing your intake, focus on the UK RNI values appropriate for your age and sex.

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 role in insulin secretion and action. Adequate dietary levels support normal glucose metabolism, though routine supplementation for diabetes prevention or treatment is not recommended by UK guidance unless deficiency is present.

• Blood pressure regulation: Through its effects on vascular smooth muscle and endothelial function, magnesium contributes to maintaining healthy blood pressure levels. However, NICE does not recommend routine magnesium supplementation for blood pressure control in the absence of deficiency.

Deficiency can impair these processes, potentially contributing to various health concerns including muscle cramps, fatigue, cardiac arrhythmias, 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. If you experience severe symptoms such as irregular heartbeat, seizures, severe weakness, or fainting, call 999 immediately.

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: Increased urinary magnesium loss occurs 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, certain antibiotics (including aminoglycosides), amphotericin B, and calcineurin inhibitors can reduce magnesium levels. The MHRA has issued a Drug Safety Update regarding PPI-associated hypomagnesaemia with prolonged use.

• 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 (normal range typically 0.7-1.0 mmol/L in adults), though this may not always reflect total body stores. Your doctor may also check calcium and potassium levels and may investigate underlying causes if you are symptomatic, potentially including an ECG.

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 (60-80 mg per 100g cooked), kale, and Swiss chard (magnesium is part of the chlorophyll molecule)

• Nuts and seeds: Almonds (80 mg per 30g serving), cashews, pumpkin seeds, and sunflower seeds

• Whole grains: Brown rice, wholemeal bread (about 30 mg per 2 slices), oats, and quinoa

• Legumes: Black beans, chickpeas, lentils, and kidney beans (40-50 mg per 100g cooked)

• 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. Bioavailability varies between formulations, with citrate and glycinate generally better absorbed than oxide. When choosing supplements, check the "elemental magnesium" content on the label, as this indicates the actual amount of magnesium provided.

Supplements are typically unnecessary for healthy individuals eating a balanced diet, but may be recommended for those with documented deficiency or specific medical conditions.

Important medication interactions: Magnesium supplements can reduce the absorption of certain medications. Separate doses by:

• Levothyroxine: at least 4 hours

• Tetracycline and quinolone antibiotics: 2-4 hours

• Bisphosphonates (e.g., alendronic acid): take bisphosphonate alone per instructions

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. The NHS does not routinely recommend magnesium supplements for the general population.

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 very high supplement doses or impaired in those with renal disease.

The UK Expert Group on Vitamins and Minerals (EVM) has established a Guidance Level for magnesium from non-food sources at 400 mg per day for adults. This guidance specifically applies to supplemental magnesium and fortified foods, not total intake from all sources, as dietary magnesium does not typically cause toxicity.

Common side effects of excessive magnesium supplementation include:

• Diarrhoea (magnesium has an osmotic laxative effect)

• Abdominal cramping and bloating

• Nausea and vomiting

These gastrointestinal symptoms often occur at doses exceeding 400 mg from supplements and typically resolve when intake is reduced. Some forms of magnesium (such as oxide or hydroxide) may cause mild diarrhoea even at lower doses.

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, who should seek medical advice before using any magnesium-containing supplements, antacids or laxatives. Those taking certain medications—including some antibiotics, bisphosphonates, and muscle relaxants—should also seek medical advice before supplementing, as magnesium can interact with these drugs.

If you experience symptoms suggestive of magnesium excess, discontinue supplementation and contact your GP promptly. For severe symptoms such as collapse, severe bradycardia, or breathing difficulties, call 999 immediately.

If you suspect an adverse reaction to a magnesium supplement, report it to the MHRA Yellow Card Scheme, which monitors the safety of medicines and supplements in the UK.

Frequently Asked Questions