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Low magnesium is easy to miss
Most people who are low in magnesium don’t know it. The symptoms tend to look like other problems: fatigue that gets attributed to a busy life, muscle cramps written off as dehydration, anxiety dismissed as stress.
Making things harder, a standard NHS blood test isn’t a reliable way to check. Serum magnesium — the fraction measured in routine blood panels — accounts for roughly 1% of the body’s total magnesium stores. The rest sits in bone, muscle, and soft tissue. You can have normal serum levels while your cells are actually running low.
A review in Clinical Kidney Journal (Jahnen-Dechent & Ketteler, 2012) describes serum magnesium as a poor marker for whole-body status, noting that significant cellular depletion can exist before any change appears in blood results.
Understanding the full range of signs gives you a better basis for deciding whether magnesium is worth investigating further.
Muscle and nerve signs
Magnesium regulates the electrical signals that cause muscles to contract and relax. When levels fall, the neuromuscular system becomes hyperexcitable — meaning muscles fire more easily than they should.
Muscle cramps
Night cramps, particularly in the calves, are one of the most commonly reported signs of low magnesium. The mechanism is straightforward: calcium drives muscle contraction, and magnesium counteracts it to enable relaxation. Without enough magnesium, muscles can lock up rather than release.
Cramps during exercise, or cramps that wake you at night, are worth noting — especially if they happen regularly and don’t seem to be relieved by hydration alone.
Eye twitching
An involuntary twitch in the eyelid (usually the lower lid) is a classic sign of magnesium insufficiency. Clinically, it’s caused by the same hyperexcitability mechanism: peripheral nerves firing without a clear trigger. Most people experience this occasionally, but if it persists for days or becomes frequent, low magnesium is one of the first things worth checking.
Restless legs
The unpleasant urge to move your legs at rest, particularly in the evening or during sleep, has a well-documented connection to magnesium status. For more on this, see our guide to magnesium and restless legs syndrome.
Numbness or tingling
Pins and needles in the hands, feet, or face that don’t have an obvious positional cause can reflect disrupted nerve signal transmission linked to low magnesium. This tends to be more pronounced in moderate-to-severe deficiency rather than mild insufficiency.
Sleep and energy signs
Difficulty falling or staying asleep
Magnesium activates the parasympathetic nervous system and regulates the GABA receptors that help quiet brain activity at night. Low magnesium is associated with lighter, more fragmented sleep and difficulty switching off in the evening.
A randomised controlled trial in the Journal of Research in Medical Sciences (Abbasi et al., 2012) found that magnesium supplementation significantly improved sleep quality, sleep duration, and early morning waking in older adults with insomnia compared to placebo. For a full breakdown of the evidence, see our post on magnesium glycinate for sleep.
Persistent fatigue
Magnesium is required at multiple steps in ATP production, the process your cells use to generate energy. It is also involved in activating over 300 enzymes across the body. When magnesium is insufficient, energy metabolism slows at a cellular level, even if everything else — thyroid, iron, sleep — looks normal on paper.
Fatigue that doesn’t respond to rest or lifestyle adjustments is worth taking seriously, and magnesium status is one of the more overlooked factors.
Mood and cognitive signs
Anxiety and low mood
Magnesium acts as a natural regulator of the HPA axis, the stress response system that governs cortisol release. When magnesium is low, the HPA axis becomes less regulated, and the brain’s stress circuits are easier to trigger.
A randomised trial published in PLOS One (Tarleton et al., 2017) found that magnesium supplementation produced significant improvements in depression and anxiety scores after six weeks, with effects comparable in scale to antidepressant medication in a mildly to moderately affected population. The improvements reversed when supplementation stopped.
For more on the specific evidence around magnesium glycinate and anxiety, see our post on magnesium glycinate for anxiety.
Brain fog and poor concentration
Difficulty with focus, slower thinking, or a general sense of mental heaviness can all reflect low magnesium. The mechanisms include impaired ATP production in neurons, dysregulated glutamate signalling (which, in excess, is excitotoxic), and the downstream effects of poor sleep on cognitive function.
This is not the same as cognitive decline, but it can affect daily functioning meaningfully and is often dismissed as stress or ageing.
Cardiovascular signs
Heart palpitations
Magnesium plays a direct role in cardiac electrical activity, helping regulate the rhythm of the heartbeat. Low magnesium can make the heart more prone to irregular beats, skipped beats, or a fluttery sensation in the chest. These are often harmless but unsettling.
Palpitations that are new, persistent, or accompanied by dizziness always warrant a GP consultation to rule out other causes. But if you have otherwise unexplained palpitations and other signs from this list, magnesium is worth investigating. See our full post on magnesium and heart palpitations.
Headaches and migraines
Magnesium deficiency is consistently associated with higher migraine frequency. The proposed mechanisms include cortical spreading depression (the electrical wave that triggers migraine aura), altered serotonin receptor function, and increased platelet aggregation.
A review in the Journal of Neural Transmission (Mauskop & Varughese, 2012) argued that all migraine patients should be considered for magnesium supplementation, noting that low magnesium is found in a significant proportion of people during acute migraine attacks. Even for tension-type headaches without aura, there is evidence that regular supplementation can reduce frequency over time.
Signs that become more common after 40
Magnesium absorption decreases with age. The kidneys also become less efficient at retaining magnesium, meaning losses increase even when dietary intake stays the same. This makes people over 40 particularly vulnerable to insufficiency.
For women, the hormonal changes of perimenopause and menopause add another layer. Oestrogen supports magnesium uptake in cells, so as oestrogen declines, magnesium insufficiency becomes more likely. This overlaps with the symptoms of menopause itself, making it harder to identify magnesium as a contributing factor.
Signs to watch for specifically in this group include: sleep disruption that worsens progressively, muscle cramps that appear for the first time in middle age, increased headache frequency, and mood changes that coincide with midlife rather than a clear external cause.
For women specifically, our post on magnesium during menopause covers the evidence in more detail.
Why blood tests often miss it
The NHS does not routinely test magnesium. When it is checked, the test measures serum magnesium, which reflects only what’s circulating in the blood at that moment — not the magnesium stored in bone, muscle, and soft tissue where it actually functions.
Because the body tightly regulates serum levels (drawing from bone reserves if needed), your blood result can appear normal until depletion is quite advanced. A result in the lower end of the reference range, even if technically “normal”, may still be associated with functional insufficiency.
This is why symptoms matter more than a single blood result when assessing whether magnesium is worth supplementing. If you have several of the signs listed here and your diet is low in magnesium-rich foods, that context is more useful than a borderline serum reading.
What to do if you recognise these signs
Dietary sources
Magnesium is found in dark leafy greens (spinach, kale), nuts and seeds (particularly pumpkin seeds and almonds), legumes, wholegrains, dark chocolate, and some fish. The UK Reference Nutrient Intake is 300mg per day for adult men and 270mg for adult women.
In practice, many UK adults fall short of these targets due to a diet high in processed foods and low in vegetables and wholegrains. Soil depletion over decades has also reduced the magnesium content of some crops.
Supplementation
If dietary changes aren’t enough, or if your symptoms are pronounced, a magnesium supplement is a practical next step. The form matters. Magnesium oxide is cheap but poorly absorbed. Magnesium glycinate (also called magnesium bisglycinate) is bound to the amino acid glycine, which significantly improves absorption and tolerability, and is the form best supported by research for sleep, anxiety, and muscle function.
It’s also worth checking whether your supplement is buffered with magnesium oxide to inflate the label number, or genuinely pure glycinate. Our post on buffered versus non-buffered magnesium glycinate explains the difference.
Our Epsilon Life Magnesium Glycinate uses pure, non-buffered magnesium bisglycinate with no oxide blending, providing 55mg elemental magnesium per capsule. It is Campden BRI tested and VeganOK certified.
When to see your GP
Heart palpitations, severe muscle weakness, or symptoms that are new and worsening should always be assessed by a doctor before attributing them to magnesium. Many of the signs listed here overlap with other conditions including thyroid dysfunction, anaemia, and vitamin B12 deficiency. It is worth ruling those out, particularly if symptoms are persistent.
FAQ
What are the first signs of magnesium deficiency?
The earliest signs are typically muscle cramps or twitching, difficulty sleeping, and fatigue that doesn’t improve with rest. Eye twitching and increased anxiety are also common early indicators. These signs are non-specific, but if several appear together, magnesium status is worth investigating.
Can low magnesium cause anxiety?
Yes. Magnesium regulates the HPA axis and GABA receptors involved in the stress response. When magnesium is low, the nervous system becomes more reactive and harder to calm. Research has found that magnesium supplementation can produce significant reductions in anxiety scores, with effects appearing within four to six weeks.
Will a blood test show magnesium deficiency?
Not reliably. Standard blood tests measure serum magnesium, which represents only around 1% of total body magnesium. Because the body maintains serum levels by drawing from bone and tissue reserves, blood results can appear normal even when cellular stores are depleted. Symptoms and dietary assessment are often more informative than a single blood result.
What causes low magnesium?
The most common causes are a diet low in magnesium-rich foods, chronic stress (which increases urinary magnesium losses), high alcohol intake, long-term use of certain medications (including proton pump inhibitors and some diuretics), and type 2 diabetes. Magnesium absorption also decreases naturally with age, making insufficiency more common in people over 40.
How long does it take for magnesium to work?
For sleep and muscle symptoms, many people notice improvement within one to two weeks of consistent supplementation. For mood and anxiety, the effects tend to build over four to six weeks. For migraine prevention, studies typically run over eight to twelve weeks before measuring outcomes. For a detailed breakdown, see our post on how long magnesium glycinate takes to work.
Which magnesium is best for deficiency symptoms?
Magnesium glycinate (bisglycinate) is the most widely recommended form for addressing deficiency symptoms. It has superior absorption compared to magnesium oxide, is gentle on the digestive system, and is the form used in most of the research on sleep, anxiety, and muscle function. Ensure the product you choose is non-buffered, meaning it contains pure bisglycinate rather than a blend with cheaper oxide.
References
- Jahnen-Dechent W, Ketteler M. Magnesium basics. Clinical Kidney Journal. 2012;5(Suppl 1):i3–i14. PubMed
- Abbasi B et al. The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. 2012;17(12):1161–1169. PubMed
- Tarleton EK et al. Role of magnesium supplementation in the treatment of depression: A randomized clinical trial. PLOS One. 2017;12(6):e0180067. PubMed
- Mauskop A, Varughese J. Why all migraine patients should be treated with magnesium. Journal of Neural Transmission. 2012;119(5):575–579. PubMed
- Gröber U et al. Magnesium in Prevention and Therapy. Nutrients. 2015;7(9):8199–8226. PubMed
This article is for informational purposes only and does not constitute medical advice. If you have persistent or worsening symptoms, speak to your GP before making changes to your diet or supplementation.
