Magnesiummmol/L
Magnesium status (poorly reflected by serum test)
Typical optimal range
0.7–1 mmol/L
A typical optimal serum magnesium range is around 0.7–1.0 mmol/L, though reference ranges vary between laboratories and should always be interpreted alongside your specific lab's reported interval. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of serum magnesium follows NHS and standard UK laboratory guidance; NICE and the Association for Clinical Biochemistry (via Lab Tests Online UK) provide the clinical framework used by GPs when acting on electrolyte results.
What is Magnesium?
Magnesium is an essential mineral that acts as a cofactor in more than 300 enzyme reactions in the body, including those involved in energy production, protein synthesis, muscle and nerve function, and blood pressure regulation. Most of the body's magnesium is stored in bone and soft tissues, with less than 1% circulating in the blood, which means a serum magnesium test only partially reflects your true magnesium status. Despite this limitation, measuring serum magnesium remains a useful screening tool — particularly for identifying significant deficiency or excess — and is routinely checked when symptoms such as muscle cramps, palpitations, or fatigue are investigated.
What a high Magnesium means
A raised serum magnesium result is uncommon and, when found, is usually a prompt to investigate an underlying cause rather than a standalone diagnosis. Your GP will likely want to review your kidney function and any supplements you are taking.
- Kidney impairment. The kidneys are the primary route for excreting excess magnesium. If kidney function is reduced — as in chronic kidney disease — magnesium can accumulate in the blood, so a raised result often prompts a check of eGFR and creatinine.
- Supplement or antacid overuse. Taking high-dose magnesium supplements or regularly using magnesium-containing antacids or laxatives can raise serum levels, particularly if kidney function is even mildly reduced. This is worth mentioning to your GP if relevant.
- Rare medical conditions. Certain hormonal disorders, such as hypothyroidism or Addison's disease, can occasionally be associated with elevated magnesium; these are uncommon but may be considered if no other cause is found.
Genuine hypermagnesaemia causing symptoms is rare in people with normal kidney function; a mildly elevated result in this context may reflect lab variation or sample handling and is often worth repeating.
What a low Magnesium means
A low serum magnesium result can be associated with symptoms such as muscle cramps, poor sleep, palpitations, fatigue, and migraines, and warrants further assessment — though it is important to know that serum magnesium can appear normal even when body stores are depleted, meaning a normal result does not completely rule out deficiency.
- Insufficient dietary intake. Diets low in vegetables, wholegrains, nuts, and seeds — which are the main dietary sources of magnesium — are a common contributor to borderline or low magnesium status in the UK population.
- Increased losses. Magnesium can be depleted by gastrointestinal conditions causing prolonged diarrhoea or malabsorption (such as coeliac disease or Crohn's disease), by excessive alcohol intake, and by certain medications including proton pump inhibitors and some diuretics, all of which increase urinary or gut losses.
Because serum magnesium reflects only a small fraction of total body magnesium, some clinicians consider a red blood cell (RBC) magnesium test to be a more sensitive indicator of deficiency; this is worth discussing with your GP if symptoms persist despite a normal serum result.
Should I be worried?
A single out-of-range magnesium result on its own rarely requires urgent action, but it is a useful conversation starter with your GP, particularly if you are experiencing relevant symptoms such as cramps, fatigue, palpitations, or disrupted sleep. Your GP may choose to repeat the test, check kidney function, review any medications or supplements that could affect magnesium levels, and consider whether further tests — such as RBC magnesium, calcium, or potassium — would be helpful, as these electrolytes are closely linked. If your result is significantly low or you have an underlying condition such as kidney disease or a gut disorder, earlier follow-up is sensible. For most people, a mildly low or mildly high result is manageable once the cause is identified.
What actually helps
Supporting healthy magnesium levels centres primarily on dietary choices, with supplementation considered where intake is consistently insufficient or losses are increased.
- Increase dietary magnesium. Prioritising magnesium-rich foods — leafy green vegetables, nuts, seeds, and wholegrains — is the most sustainable and well-evidenced way to maintain adequate status; food-based magnesium is generally well absorbed and comes alongside other beneficial nutrients.
- Reduce alcohol intake. Regular alcohol consumption increases urinary magnesium excretion and can deplete body stores over time; reducing intake in line with UK Chief Medical Officers' low-risk guidelines (no more than 14 units per week) supports better magnesium retention.
- Review medications with your GP. If you are taking proton pump inhibitors (PPIs) long-term or certain diuretics, discuss with your GP whether your magnesium should be monitored regularly, as these medications are a recognised cause of low magnesium levels.
- Consider a supplement if advised. Magnesium glycinate (typically in the range of 200–400 mg elemental magnesium per day) is considered well tolerated with good bioavailability, but supplementation is best discussed with your GP or pharmacist, especially if you have kidney problems or take other medications.
There is good supporting evidence that the following foods contribute meaningfully to magnesium intake as part of a balanced diet.
Leafy green vegetables
Vegetables such as spinach, kale, and Swiss chard are rich in magnesium because the mineral is a central component of chlorophyll, the pigment that makes plants green.
Nuts and seeds
Pumpkin seeds, almonds, cashews, and sunflower seeds are among the most concentrated food sources of magnesium and also provide healthy fats and protein.
Wholegrains
Foods such as brown rice, wholemeal bread, oats, and quinoa retain the magnesium-rich bran and germ layers that are removed during refining, making them significantly better sources than their white or refined equivalents.
Legumes
Beans, lentils, chickpeas, and edamame are good plant-based sources of magnesium and are widely recommended within NHS dietary guidance for overall healthy eating.
Dark chocolate (70%+ cocoa)
High-cocoa dark chocolate contains a notable amount of magnesium per serving; while it should be eaten in moderation, it is a genuinely useful contributor to intake for those who enjoy it.
Fish
Oily and white fish such as mackerel, salmon, and haddock provide moderate amounts of magnesium alongside other nutrients including omega-3 fatty acids and vitamin D.
Track your own Magnesium
Upload a lab PDF and Better Days trends Magnesium over time, flags it when it drifts, and suggests foods that help.
More in Vitamins/Minerals
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.