Magnesium matters, but tiredness and muscle cramps are poor evidence of a deficiency. Here’s when to look at your diet, check your medicines and ask about a test.
Reviewed, edited and approved by Editor-in-chief Daniel Sköld · Updated 23 October 2026
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By the time you’ve reached midlife, a stiff calf and a rubbish night’s sleep can make a supplement advert sound unusually persuasive. Magnesium is often cast as the missing piece: take a tablet, recover better, wake up transformed. If only.
Low magnesium is real, and sometimes important. But tiredness, cramps and stress do not tell you what your magnesium level is. The useful question is not whether magnesium matters. It is whether you have a reason to suspect you’re low — and what else might explain how you feel.
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Is tiredness a sign of low magnesium?
It can be. Magnesium helps your body use energy and supports normal muscle and nerve function. Low blood magnesium may cause lethargy, weakness or cramps; more severe cases can affect the heart’s rhythm. None of those symptoms, though, belongs exclusively to magnesium deficiency. Your calves have not sent a laboratory report.
Persistent tiredness can also come from poor sleep, stress, low mood, medicines or conditions such as anaemia, diabetes and thyroid problems. If you snore loudly, wake gasping or feel sleepy through the day, sleep apnoea deserves attention. A magnesium tablet will not fix interrupted breathing at night.
Nor does feeling worn out prove your testosterone has fallen. There is interest in magnesium and male hormones, but research on micronutrient supplements has not established a reliable testosterone boost for men in midlife. If you have persistent changes in sex drive or erections as well as fatigue, tell your GP rather than buying a product marketed as a hormonal reset.
The distinction matters because chasing one fashionable explanation can delay a more useful conversation. Notice when symptoms started, whether they are worsening, how you sleep and whether they interfere with work or ordinary life. That information will do more for a GP appointment than a drawer full of half-used tubs.
The medicine-cupboard clue
Diet is not the only reason magnesium can fall. Ongoing diarrhoea or problems absorbing nutrients can reduce it. Some medicines can contribute too, particularly diuretics, often called water tablets, and proton pump inhibitors used for acid reflux, such as omeprazole and lansoprazole.
The UK medicines regulator has warned that low magnesium has been reported infrequently with prolonged use of proton pump inhibitors. It advises healthcare professionals to consider checking levels before and during long-term treatment, especially when someone also takes a diuretic or digoxin. That is a reason for a medicines review, not a reason to throw your prescription in the bin.
The best clue to low magnesium may be in your medical history, not in your muscle cramps.
If you have been taking a reflux medicine for a long time, bring it up with your GP or pharmacist, including anything you buy over the counter. Mention water tablets, digestive problems and any previous low potassium or calcium result. Your clinician can decide whether a magnesium blood test belongs alongside other checks and whether your medicines need reviewing.
Having a risk factor does not mean you have a deficiency. Equally, a balanced diet cannot always overcome a problem with absorption or losses. That is why the sensible next step depends on your circumstances, not on how convincingly an advert describes your Tuesday afternoon.
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Should you take a magnesium supplement?
For most people, food is the straightforward starting point. The NHS says men aged 19 to 64 need 300mg of magnesium a day and should be able to get it from a varied, balanced diet. Wholemeal bread, spinach and nuts are useful sources. Beans, seeds and other wholegrains make it easier to build a decent pattern of eating rather than hunt for a single magic ingredient.
Think ordinary meals: porridge with seeds, beans with a jacket potato, or a handful of unsalted nuts with lunch. You need not calculate every milligram. If your diet has become mainly takeaway meals and toast eaten over the sink, improving it has more going for it than buying whichever magnesium powder has the most scientific-looking label.
Supplements have a place when a clinician recommends them for a specific problem. As a general purchase for better sleep, less stress, improved recovery or higher testosterone, the case is much weaker. If you are considering one, ask what you expect it to change and how you would know it had helped. A vague promise to feel ‘optimised’ is difficult to test.
More is not automatically better. The NHS says doses above 400mg of magnesium from supplements can cause diarrhoea, and advises against taking too much; it says 400mg or less daily from supplements is unlikely to cause harm for most people. That figure refers to supplements, not magnesium naturally present in food. Check the stated magnesium amount and remember that multivitamins, antacids or other products may add to what you take.
Speak to a pharmacist or GP before supplementing if you have kidney disease or take regular medicines. Kidney problems can make excess magnesium harder to manage, while magnesium products can interfere with the absorption of some medicines. Do not try to treat suspected deficiency with repeated high doses: if the cause is continuing, the tablets may simply give you diarrhoea and leave the real problem untouched.
When should you ask for a blood test?
Book a GP appointment if tiredness has lasted several weeks without an obvious reason, affects daily life or comes with other symptoms. Be specific about cramps, weakness, digestive trouble, changes in sleep and every medicine or supplement you use. A GP may consider a magnesium blood test if your symptoms and risks warrant it; tests for other possible causes of fatigue may be more useful. Testing is a decision to make with a clinician, not a competition to order the longest panel.
In England, eligible adults aged 40 to 74 can have a free NHS Health Check, generally offered every five years. It assesses risks such as heart disease and diabetes; it is not a magnesium-deficiency test or a substitute for an appointment about symptoms. That particular programme is for England. In Scotland, Wales and Northern Ireland, ask your GP practice about appropriate checks and assessment if you are concerned; do not wait for a Health Check invitation that does not apply where you live.
Get urgent advice through NHS 111 if you have worrying symptoms and are unsure what to do. Call 999 if palpitations occur with chest pain, severe breathlessness or fainting. Most tiredness and cramps are not emergencies, but an irregular heartbeat accompanied by those symptoms is not something to investigate with a supplement aisle and a search engine.
In short
Tiredness, stiffness and cramps alone cannot tell you whether you have low magnesium. Start with a varied diet, and speak to your GP or pharmacist if symptoms persist, you have digestive problems or you take medicines that may lower magnesium. Supplements are not a proven shortcut to better recovery or testosterone, and a clinician can advise whether testing makes sense for you.
Adrian Irving writes about health for men 45 and over who would rather do something than worry. Training, weight loss, sleep, cholesterol and blood tests, heart health, testosterone, the prostate, mental health and your sex life – what the evidence says, what's worth trying, and when it's time to see your GP.
One of Midcent's writers. Spotted something? Write to adrian@midcent.uk.
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