The pattern shows up in your sleep
If you're trying to work out whether magnesium might be running low, the most reliable place to start is the night. Not the difficulty getting off to sleep, which has its own long list of causes. More specifically: calf cramps that wake you, restless legs that need you to move them, and the particular kind of sleep that clocks in at a reasonable number of hours but still leaves you unrefreshed by morning.
During the day, some people notice irritability or a low-level anxiety that doesn't have a clear cause. Headaches can sit in this picture too. None of these symptoms are specific to magnesium alone, but the cluster of them, and especially the night-time muscle pattern, is where the question is worth asking.
Sleep first, then magnesium
There's a sensible order to this. If sleep itself hasn't been addressed, magnesium isn't the first thing to look at. Inconsistent bedtimes, screens in the hour before sleep, caffeine after midday, a room that's too warm, alcohol in the evening: any of these can produce the same tired-but-unrefreshed pattern that magnesium deficiency creates. Fixing the habit usually fixes the sleep.
If you've already done that work, or you're confident your sleep habits aren't the culprit, then the food side is worth a look. The overnight cramps and restless legs, in particular, tend to persist through better sleep habits if there's a nutrient shortfall underneath.
What magnesium actually does
The NHS describes magnesium as a mineral that "helps turn the food we eat into energy" and supports the parathyroid glands that regulate bone health. That's part of it. The fuller picture: magnesium is involved in around 300 enzyme reactions in the body, and two of the most relevant to the patterns above are muscle relaxation and nervous-system regulation.
Muscles need both calcium and magnesium to work properly. Calcium triggers a contraction; magnesium helps release it. When magnesium runs low, that release becomes less reliable, which is why calf cramps at night are a common early signal. The nervous system link explains the anxiety and irritability: magnesium helps regulate neurotransmitter signalling, and when the supply dips, the system can tip toward over-activation.
The numbers
The NHS sets the target at 300mg a day for men and 270mg a day for women aged 19 to 64. Most adults eating a reasonably varied diet clear this without trying. The shortfall tends to show up in people eating very few vegetables over a sustained period, or drinking heavily, since alcohol increases the amount of magnesium the kidneys excrete. Both are factors the NHS specifically calls out.
It is worth noting that magnesium is not on the standard NHS blood panel. A GP asked about it will likely be running tests for thyroid function, full blood count, vitamin D, iron, or electrolytes. They probably will not test magnesium specifically unless there's a strong clinical reason. The right framing for a GP visit, if symptoms persist, is the broader picture of sleep, muscle function, and mood, not a direct request for a magnesium test.
The food side
The NHS names spinach, nuts, and wholemeal bread as its headline sources. That's the shortlist. In practice, a handful of foods do disproportionate work for their portion size.
None of these require a special shop. They're already in most supermarkets, and the easiest move is usually to make pumpkin seeds a regular addition to porridge or a salad, and to keep almonds in the cupboard as a default snack.
On the supplement question
The magnesium-for-sleep supplement market is extremely loud at the moment. There are compelling claims about magnesium glycinate, magnesium threonate, and various other forms. Some of this evidence is real; some of it is amplified by the commercial interest behind it.
It is worth being honest about what we are here. We track food. The food conversation and the supplement conversation are genuinely different ones. Food magnesium comes packaged with fibre, protein, and other minerals, none of which come in a tablet. If you are eating very few magnesium-rich foods, fixing that is the first thing to try. Give it two weeks before reaching for a supplement.
If you do want to consider a magnesium supplement after that, the NHS notes that taking 400mg or less a day is unlikely to cause harm, though higher doses can cause diarrhoea. A conversation with a pharmacist is the right next step, not a 600mg dose from an influencer recommendation. They can help you choose a form and dose that fits your situation.
When to see your GP
If the sleep and muscle patterns persist after two or three weeks of consistent attention to the food side and decent sleep habits, a GP visit is worth it. Go with the full picture: what the sleep looks like, when the cramps happen, whether anxiety has changed, how diet has shifted.
They are unlikely to test magnesium directly. What they will do is triage the broader landscape: thyroid, iron, vitamin D, electrolytes, and sleep patterns. Any of those could be contributing. The GP visit is to rule out the things a blood test can check, not to get a magnesium result specifically. That honesty matters when you are preparing for the appointment.
A short, honest note
This page is a pattern guide, not a clinic. What you read here is drawn from NHS guidance on magnesium and on nutrition generally. If a pattern keeps fitting after you have spent a few weeks on the food side, see your GP. They will run the right tests and read them properly, which is the part a blog cannot do.