There's a particular kind of exhaustion many women know well. The body feels completely drained, but the mind won't slow down. You get into bed expecting sleep to come easily, and instead your thoughts keep moving, your body stays tense, and real rest feels just out of reach.
This is often called tired but wired, and it has less to do with "not trying hard enough to relax" and more to do with a nervous system that's been carrying too much for too long. Magnesium comes up often in this conversation, sometimes oversold as a miracle mineral, sometimes dismissed as overhyped. The truth, as usual, sits somewhere more interesting in between.
Why the Nervous System Gets Stuck in "On"
Think of the nervous system as having an accelerator and a brake. The accelerator is the excitatory system, the signals that sharpen focus and mobilise you for action. The brake is the inhibitory system, led by a neurotransmitter called GABA, whose job is to quieten things back down once a threat has passed. Under chronic stress, that braking system can become less effective over time. The nervous system fires up in response to a difficult day and, instead of returning fully to neutral, settles at a slightly higher resting level than before. Repeated over months, the baseline shifts: low-level situations start to register as bigger threats than they are, irritability rises, and the brain struggles to switch off even when the body is exhausted.
This connects to the HPA axis, the hypothalamic-pituitary-adrenal system that governs the body's stress response and ends with the release of cortisol. Cortisol isn't the villain it's sometimes made out to be, it mobilises energy and sharpens focus when genuinely needed. The issue is that this machinery is built for short bursts, not sustained activation. Under prolonged pressure, cortisol can spike more easily, stay elevated longer, and take more time to settle.
Where Magnesium Fits In
Magnesium is a cofactor in over 300 enzymatic reactions in the body, and several of them relate directly to this picture.
It appears to play a role at NMDA receptors, channels on nerve cells that let calcium in when a genuine signal arrives. When these become overactive, the resulting flood of calcium is associated with the kind of neural hyperexcitability behind racing thoughts and restlessness. Magnesium is thought to help regulate how readily these channels open, functioning somewhat like a gatekeeper for that process.
It's also involved in GABA activity, the nervous system's main calming pathway. Magnesium doesn't produce calm directly; the research suggests it helps the GABA system function as intended, supporting the brain's own capacity to quieten itself rather than creating that effect independently.
And it interacts with the stress-response cascade itself. When magnesium status is adequate, research suggests it may help moderate the signalling chain that leads to cortisol release, supporting a more efficient return to baseline after a stressful event, rather than preventing stress from occurring in the first place.
The Stress-Depletion Cycle
Here's where it becomes genuinely self-reinforcing. Elevated cortisol increases how much magnesium the body excretes through urine. Lower magnesium is associated with a more reactive nervous system. A more reactive nervous system produces more frequent cortisol responses. Researchers have described this as a "vicious circle," a pattern that's been studied since the early 1990s: each stress response depletes some of the very mineral that helps regulate the next one.
This cycle tends to be slow and cumulative, often taking months to become noticeable, which is part of why it can go unrecognised for a long time. It isn't about one bad week. It's the low-grade, always-on kind of stress, the mental load that never quite switches off, that does the real cumulative work here.
Why Perimenopause Can Turn the Volume Up
Oestrogen supports magnesium uptake into cells and influences the sensitivity of GABA and serotonin pathways, two of the nervous system's key calming and mood-regulating systems. As oestrogen fluctuates unpredictably during perimenopause, rather than declining smoothly, that cellular magnesium balance can become less stable. A 2025 review in Nutrients found that sex-based hormonal differences significantly affect magnesium metabolism, identifying perimenopausal women as among those most vulnerable to subclinical deficiency, meaning below the threshold that shows up on a standard blood test, yet still meaningful in the body.
Progesterone adds another layer. It metabolises into a compound that has a calming effect on GABA receptors, so as progesterone declines, that built-in buffer weakens too. Even before perimenopause, this shows up cyclically: during the luteal phase of the menstrual cycle, progesterone metabolism increases and, with it, the body's demand for magnesium.
Why a Normal Blood Test Doesn't Rule This Out
Standard serum magnesium tests measure only what's circulating in the blood at that moment, and less than 1% of the body's total magnesium actually lives there. The other 99% is inside cells, muscles, and bone. When blood levels start to dip, the body is generally good at pulling from those deeper stores to keep blood readings looking normal, which means a "normal" result doesn't necessarily reflect how much magnesium is actually available at a cellular level. An RBC (red blood cell) magnesium test, which measures magnesium inside cells rather than in the bloodstream, is a more informative option worth discussing with your GP if symptoms persist despite a normal standard panel.
What the Clinical Evidence Actually Shows
A 2024 systematic review by Rawji and colleagues, published in Cureus, examined 15 interventional trials against strict inclusion criteria. Of the studies measuring anxiety outcomes, 5 of 7 reported meaningful improvements; of those measuring sleep, 5 of 8 reported improvements in sleep parameters. It's worth being transparent about a limitation here: the majority of trials in this review used magnesium oxide, a poorly absorbed form, which makes the results encouraging in direction but not necessarily specific to the better-absorbed forms most commonly recommended for sleep and anxiety support.
A 2017 systematic review in Nutrients, examining 18 studies across anxiety-vulnerable populations, concluded the evidence was "suggestive of a beneficial effect on subjective anxiety," while explicitly rating overall evidence quality as poor and calling for larger, better-designed trials. That honest assessment still holds today: the biological mechanisms are well-established and plausible, the clinical results are encouraging in the populations studied so far, but magnesium is not a medication and hasn't been tested against first-line anxiety treatments.
Two anxiety trials in the 2024 review that showed no significant improvement both involved women with hormonal factors at play (one in premenstrual symptoms, one postpartum). That's a genuinely useful thing to know rather than a reason for pessimism: it suggests the research hasn't yet caught up with the more complex biology of hormonal transitions, not that magnesium is irrelevant for women navigating them.
Supporting Magnesium Through Food
Food is the foundation. Whole foods deliver magnesium alongside fibre, healthy fats, and other co-factors that support absorption in ways that are harder to replicate through supplementation alone. Useful sources include pumpkin seeds (around 150mg per ounce), dark leafy greens, almonds and cashews, black beans and other legumes, wholegrains like quinoa, avocado, and dark chocolate.
That said, research suggests a substantial proportion of adults don't consistently meet magnesium requirements through diet alone, partly because modern food processing and soil depletion mean whole foods often contain less magnesium than they once did. During periods of heightened demand, such as perimenopause or sustained stress, the body can burn through magnesium faster than a balanced plate reliably replenishes it. That's a reasonable, honest gap, not a reason to feel you're doing something wrong.
When to Speak to Your GP
If you're experiencing frequent or significant heart palpitations, fatigue that isn't improving with rest, or symptoms meaningfully affecting daily life, these are good reasons to speak to your GP. It's also worth raising if you suspect perimenopause may be playing a role, or want to rule out overlapping causes like thyroid changes, anaemia, or B12 deficiency, all of which can produce similar symptoms.
The Takeaway
What you're experiencing, if this resonates, isn't weakness or overthinking. There's a genuine, well-documented biological basis for a nervous system that's stuck in a low-grade state of alert, and magnesium plays a real, evidenced (if not yet fully conclusive) role in how that system regulates itself. The research doesn't support magnesium as a cure-all, and it's honest to say so. But it's also not nothing, and for women navigating the additional hormonal complexity of perimenopause, understanding the mechanism is a genuinely useful starting point.
Sources: Rawji A, et al. Examining the Effects of Supplemental Magnesium on Self-Reported Anxiety and Sleep Quality: A Systematic Review, Cureus 16(4):e59317, 2024. A systematic review of magnesium's beneficial effect on subjective anxiety in anxiety-vulnerable samples, Nutrients, 2017. Review of sex-based hormonal differences in magnesium metabolism, Nutrients, 2025.