Last updated: October 2026
Early signs of low magnesium include tiredness, muscle cramps or twitches, weakness, poor appetite and feeling sick. More severe deficiency can cause numbness, tingling and an irregular heartbeat, which needs urgent medical care. True deficiency is uncommon in healthy people eating a varied diet, and is more likely with long-term acid-reducing medicines, diuretics, heavy drinking or gut conditions.
Below: signs to watch for, who’s most at risk, how it’s tested, what to do, and food sources.
Signs of magnesium deficiency
| Stage | Possible signs |
|---|---|
| Early or mild | Tiredness, weakness, loss of appetite, feeling sick, muscle cramps, eyelid twitches |
| More severe | Numbness or tingling, muscle spasms, tremors, irregular or fast heartbeat, low calcium or potassium levels, seizures |
These signs are common and have many causes, including poor sleep, stress, low iron or B12, and thyroid problems, so they don’t prove you’re low in magnesium. Get a racing or irregular heartbeat, fainting or seizures checked urgently: call 111, or 999 in an emergency.
Who’s most at risk?
| Risk factor | Why |
|---|---|
| Long-term proton pump inhibitors (such as omeprazole) | The MHRA warns they can cause low magnesium, usually after a year or more |
| Diuretics (water tablets) | Increase magnesium loss in urine |
| Heavy drinking | Reduces absorption and increases losses |
| Gut conditions such as Crohn’s or coeliac disease, or long-lasting diarrhoea | Reduce absorption |
| Type 2 diabetes | Higher losses in urine |
| Older age | Lower intake and absorption |
| Low intake of whole foods | Diets low in nuts, seeds, greens and wholegrains |
How is low magnesium tested?
Your GP can check magnesium with a blood test. Only about 1% of the body’s magnesium is in the blood, so a normal result doesn’t always rule out low stores, but a low result is meaningful. Doctors usually check it alongside calcium and potassium, especially if you take medicines that lower magnesium.
What to do if you think you’re low
- Eat more magnesium-rich foods first (see below).
- Ask your GP for a blood test if you have symptoms or a risk factor.
- Consider a supplement: the NHS says 400mg a day or less from supplements is unlikely to cause harm. Glycinate and citrate are well absorbed. See best magnesium supplement UK.
- Give it time: see how long magnesium takes to work.
Magnesium contributes to the reduction of tiredness and fatigue, normal muscle function and normal psychological function. Severe deficiency is treated by doctors, sometimes with magnesium through a drip. Don’t take supplements if you have kidney disease unless advised. For other reasons you might feel drained, see why am I always tired?
Our Magnesium Glycinate Sleep Complex gives 148mg of magnesium per serving from bisglycinate and citrate, as an evening drink. We don’t recommend our products during pregnancy or breastfeeding.
Foods high in magnesium
| Food group | Examples |
|---|---|
| Nuts and seeds | Pumpkin seeds, almonds, cashews |
| Leafy greens | Spinach, kale |
| Wholegrains | Wholemeal bread, oats, brown rice |
| Beans and pulses | Black beans, chickpeas, lentils |
| Other | Dark chocolate, bananas, avocado |
The NHS says adults need 300mg (men) or 270mg (women) a day, and most people can get this from a varied diet. See magnesium for cramps and magnesium for sleep.
For the full list with amounts per portion, see foods high in magnesium.
FAQs
What are the first signs of low magnesium?
Tiredness, weakness, loss of appetite, feeling sick and muscle cramps or twitches. These are common and have many other causes.
How do I know if I need magnesium?
Look at your diet and risk factors, and ask your GP for a blood test if you have symptoms or take medicines that lower magnesium.
Can low magnesium cause anxiety or poor sleep?
Low magnesium can contribute to tiredness and irritability, but anxiety and poor sleep have many causes. See our guides to magnesium for anxiety and sleep.
Do omeprazole and other PPIs lower magnesium?
Yes, with long-term use. The MHRA advises doctors to consider checking magnesium in people on them for a long time.
How long does it take to fix low magnesium?
Mild low intake improves over weeks with diet or supplements. Severe deficiency needs medical treatment.
Sources
- NHS. Vitamins and minerals: magnesium.
- MHRA. Proton pump inhibitors in long-term use: reports of hypomagnesaemia.
- Gröber U et al. Magnesium in prevention and therapy. Nutrients, 2015.
