"You're just stressed" is the sentence Rachel Ainsworth heard from three different GPs over eight months before a blood test finally showed what was actually going on. The 41-year-old marketing consultant from Manchester had the muscle twitches, the crushing fatigue by mid-afternoon, the eyelid that wouldn't stop flickering during meetings. Her magnesium level, when someone finally checked it, was well below range. "Nobody suggested the test until I asked for it myself," she says. "Everything I described fit a stress diagnosis just as well, so that's where it stayed."
Why the symptoms and "just stress" overlap so completely
Magnesium is involved in more than 300 enzymatic reactions in the body, including the ones that regulate the nervous system's response to stress hormones, muscle contraction, and sleep architecture. That overlap is exactly the problem: low magnesium produces anxiety-like symptoms, disrupted sleep, muscle tension, and fatigue — the same cluster GPs are trained to associate first with stress, poor sleep hygiene, or a low-level anxiety disorder. A ten-minute consultation genuinely doesn't have room to work through both possibilities properly, and magnesium deficiency doesn't show up on a standard blood panel unless someone specifically requests serum magnesium, which most routine bloodwork in the NHS doesn't include by default.
The symptoms that get dismissed most often
Eyelid twitching, or myokymia, is the one patients mention most and doctors take least seriously — it's genuinely common with stress and poor sleep alone, so a clinician has no strong reason to suspect magnesium first. Muscle cramps, particularly calf cramps at night, are the second most dismissed symptom, often chalked up to dehydration or simply getting older. Persistent fatigue that doesn't lift with rest, heart palpitations that show up on no cardiac workup, and a specific kind of restlessness that feels physical rather than purely mental round out the pattern that specialists increasingly flag as worth a magnesium check before anything more invasive.
None of these symptoms alone points clearly at magnesium. Together, and especially alongside a diet heavy in processed food or a history of type 2 diabetes, IBS, or regular alcohol use — all of which impair magnesium absorption or increase how much the body loses through urine — the pattern is worth naming to a GP directly rather than accepting a stress diagnosis by default.
Who's actually at risk, and it's more people than "deficient diet" suggests
The obvious risk group is anyone eating a diet low in leafy greens, nuts, seeds, and whole grains — the foods that carry most of the UK's dietary magnesium. But several conditions and medications quietly drain magnesium regardless of diet. Proton pump inhibitors like omeprazole, taken long-term by millions of people in the UK for reflux, are associated with reduced magnesium absorption and carry an MHRA warning about this specific risk. Type 2 diabetes increases magnesium loss through the kidneys. Regular alcohol consumption above moderate levels impairs both absorption and retention. Women on hormonal contraception and anyone dealing with chronic stress — which increases cortisol, and cortisol increases magnesium excretion — sit in a genuine risk category that has nothing to do with how healthy their diet looks on paper.
What the actual numbers look like
Normal serum magnesium sits between roughly 0.7 and 1.0 mmol/L, and anything below that range technically counts as hypomagnesemia. Here's the complication specialists keep raising: serum magnesium only reflects about 1% of the body's total magnesium, since the rest sits inside cells and bone. A patient can have a "normal" blood result and still be functionally deficient at the cellular level, which is part of why this gets missed even when a test is actually run. Some clinicians now push for a red blood cell magnesium test instead, which gives a more accurate picture, though it's not yet standard on the NHS and usually needs to be requested privately or through a specialist.
Food first — and which foods actually move the needle
Pumpkin seeds are the standout food source, delivering roughly 150mg per 30g serving against an adult RDA of 300mg for men and 270mg for women. Dark chocolate above 70% cocoa, spinach, almonds, black beans, and whole grains like brown rice and oats all contribute meaningfully, and a diet built around these — rather than one relying on a supplement to compensate for consistently low intake — is the better foundation by a wide margin. Supplements have a role, particularly magnesium glycinate for anyone whose main symptom is disrupted sleep, since it's better absorbed and less likely to cause the digestive upset that magnesium citrate or oxide often trigger at higher doses. Don't reach for a supplement as the first move if a GP hasn't confirmed low levels — self-supplementing at high doses can cause diarrhoea and, in people with reduced kidney function, a genuinely dangerous magnesium build-up.
Migraine, PMS, and restless legs — the conditions with the strongest evidence link
Magnesium is one of the few supplements a neurologist will actually recommend with confidence, and the evidence for migraine is genuinely solid rather than the usual wellness-industry overstatement. Studies reviewed by the American Migraine Foundation have shown magnesium oxide or citrate, taken daily as a preventive rather than during an attack, reduces migraine frequency in people with documented low magnesium — and low magnesium turns up disproportionately often in migraine patients compared with the general population. That's a genuinely different use case from the "it might help with everything" framing magnesium sometimes gets online, and it's worth raising specifically with a GP or neurologist if migraines are part of the picture alongside the fatigue and muscle symptoms.
Premenstrual syndrome is the other area with real trial evidence behind it, particularly for the mood and bloating symptoms rather than cramping specifically. Restless legs syndrome sits in a murkier spot — some patients report genuine improvement, but the trial evidence is thinner and more mixed than for migraine, so it's worth treating as worth trying rather than a guaranteed fix.
The supplement aisle isn't as simple as "buy magnesium"
Every compound on the shelf is a different absorption story.
Walk into a Boots or Holland & Barrett and the magnesium shelf alone can run to a dozen different compounds, and the differences aren't marketing fluff — they change how much actually gets absorbed and what side effects show up. Magnesium oxide is the cheapest and most common form on general supermarket shelves, but it's also the least well absorbed, with some research suggesting less than 5% of the dose is actually taken up by the gut; most of it does its work as a laxative on the way through, which is why it's sold separately as a constipation remedy under brands like Milk of Magnesia. Magnesium citrate absorbs considerably better and is a reasonable general-purpose choice, though it can still cause loose stools at higher doses. Magnesium glycinate is the form most specialists point toward for sleep and anxiety-adjacent symptoms specifically, because the glycine itself has a mild calming effect independent of the magnesium, and it's gentler on digestion than citrate or oxide.
Magnesium threonate is the newest and most expensive option, marketed heavily on its ability to cross the blood-brain barrier more effectively — the early research is genuinely interesting, but it's nowhere near robust enough yet to justify the roughly triple price tag over glycinate for most people. Price varies enormously for what's nominally the same nutrient: a month's supply of basic magnesium oxide tablets costs under £3 at most pharmacies, while the same month of a branded glycinate or threonate product can run £15 to £25. That price gap isn't scaled to the actual benefit difference in most cases — it mostly reflects absorption quality up to the glycinate tier, then diminishing returns after that.
What it looks like when a GP takes it seriously
Doctors who do investigate magnesium properly tend to follow a similar pattern: a serum test as the first, cheap screen, dietary history to check for the obvious gaps, a review of current medication for anything — PPIs especially — known to interfere with absorption, and only then a supplement recommendation matched to the dominant symptom. That's a fifteen-minute process end to end, most of it just asking the right questions in the right order. The gap isn't clinical complexity; it's that magnesium doesn't have a dedicated referral pathway or a routine screening trigger the way thyroid function does, so whether it gets caught depends heavily on an individual GP thinking to consider it rather than a system that prompts them to.
Getting a GP to actually order the test
Ask specifically for a "serum magnesium" blood test rather than describing symptoms and letting the GP choose which panel to run — a standard full blood count and metabolic panel doesn't automatically include it, and it needs to be requested by name. Bring a symptom list written down beforehand, including duration and frequency, because the pattern reads very differently on paper than it does described verbally in a rushed ten-minute appointment. If the first GP is reluctant, that's worth pushing back on directly rather than accepting "it's probably stress" as the final word — magnesium testing is inexpensive, low-risk, and takes one blood draw to rule in or out.
Rachel's level normalised within six weeks of starting a prescribed glycinate supplement alongside dietary changes, and the eyelid twitch — the symptom she'd been most embarrassed to keep mentioning to doctors who clearly thought it was minor — was gone within ten days. "The frustrating part wasn't the deficiency," she says. "It was how long 'you're just stressed' was treated as a full explanation instead of a starting point for an actual test."