Magnesium deficiency: symptoms you might not recognise and how to check

Inadequate dietary intake from modern food

The magnesium content of food has fallen significantly over the past 60 years, with intensive farming practices reducing soil mineral levels by up to 30%. Processing strips further magnesium from grains — by up to 80% in some cases. The result is that even people eating what they consider a nutritious diet may be consistently below the NHS recommended intake of 300mg per day for men and 270mg for women. Magnesium-rich foods include dark leafy greens (spinach, kale), nuts and seeds (pumpkin seeds, almonds), legumes, wholegrains, and avocado — but these are often absent in quantity from typical UK diets.

Chronic stress and the magnesium-stress vicious cycle

Stress causes the body to excrete more magnesium via the kidneys. This is well-established at a biochemical level: the stress response elevates cortisol, which increases urinary magnesium losses. Lower magnesium then makes the nervous system more reactive to stress — reducing GABA activity, the inhibitory neurotransmitter that promotes calm. The result is a self-reinforcing cycle: stress depletes magnesium, and depleted magnesium amplifies the stress response. This pattern is particularly relevant for people experiencing persistent anxiety, poor sleep, or burnout who assume those symptoms are purely psychological.

Gut malabsorption and digestive conditions

Magnesium is absorbed in the small intestine. Conditions that compromise gut integrity or accelerate transit — including Crohn's disease, coeliac disease, and prolonged diarrhoea — significantly reduce absorption. People with inflammatory bowel conditions are at higher risk of magnesium deficiency regardless of dietary intake. Even subclinical gut dysbiosis, which affects the composition and function of the microbiome, can impair mineral absorption over time.

Medications that lower magnesium levels

Proton pump inhibitors (PPIs) — omeprazole, lansoprazole, and similar drugs used to reduce stomach acid — are among the most common causes of magnesium deficiency in the UK. Long-term PPI use is associated with clinically significant magnesium depletion. Diuretics (prescribed for blood pressure and fluid retention) also increase urinary magnesium excretion. Certain antibiotics and immunosuppressants carry similar effects. If you take any of these medications long-term, periodic magnesium monitoring is a reasonable precaution.

Type 2 diabetes and insulin resistance

People with type 2 diabetes have significantly higher rates of magnesium deficiency, driven by increased urinary losses linked to elevated blood glucose. The relationship runs in both directions: magnesium plays a role in insulin sensitivity, and deficiency may impair glucose metabolism, making blood sugar harder to control. Magnesium deficiency is also closely associated with metabolic syndrome, which clusters with insulin resistance, high triglycerides, and cardiovascular risk.

Alcohol consumption and gastrointestinal losses

Alcohol increases renal magnesium excretion and reduces absorption in the gut, while also being associated with inadequate dietary intake. Even moderate regular alcohol consumption can contribute to gradually declining magnesium status over time, without reaching the levels typically associated with clinical alcoholism.

The most common challenge with magnesium testing is that standard serum magnesium — the version measured in a routine blood draw — reflects only the 1% of magnesium that circulates in the blood. Approximately 60% is stored in bone and around 40% in muscle and soft tissue. This means blood magnesium levels can appear normal even when intracellular stores are genuinely depleted. It is possible to have a normal serum magnesium result while experiencing real functional deficiency.

That said, serum magnesium remains the most practical and widely available measurement, and when interpreted alongside symptoms, medications, and other relevant biomarkers, it provides useful clinical information. A result below 0.70 mmol/L is considered clinically low; mild deficiency in the range of 0.50-0.70 mmol/L is estimated to affect 2.5-15% of the general population and often goes undetected.

The more important point for most people is what to test alongside magnesium, because the mineral does not act in isolation. Low magnesium suppresses parathyroid hormone and impairs potassium reuptake in cardiac cells — which means persistent magnesium deficiency can contribute to low calcium and low potassium levels. Testing the full electrolyte and nutrient picture is more informative than magnesium alone.

The standard NHS panel does not routinely include magnesium. If you have persistent symptoms — particularly muscle cramps, poor sleep, anxiety, or unexplained fatigue — and are taking medications known to deplete magnesium, requesting a test through your GP or a private blood test is a reasonable step. Results should be interpreted in the context of your symptoms and any other relevant markers.

Dietary changes that make a measurable difference

Increasing dietary magnesium is the first line of approach. The most magnesium-dense foods accessible in the UK include: pumpkin seeds (one of the richest sources per gram), dark chocolate (70%+), almonds and cashews, spinach and Swiss chard, edamame, black beans and lentils, and wholegrain bread and oats. Swapping refined grains for wholegrains is one of the most practical ways to incrementally improve magnesium intake without significant dietary overhaul.

Addressing the stress-magnesium loop

Because stress both depletes magnesium and is worsened by magnesium deficiency, addressing the physiological stress response is part of managing magnesium status — not separate from it. Practices that measurably reduce cortisol output, including consistent sleep timing, low-intensity exercise, and structured recovery, directly reduce urinary magnesium losses. Research shows that magnesium supplementation of 300mg daily reduced cortisol levels and improved heart rate variability in people under regular stress. Tracking both your stress markers and your magnesium levels over time shows which interventions are actually making a difference for your biology.

Sleep and magnesium's role in GABA function

Magnesium is essential for the function of GABA receptors, which regulate the nervous system's ability to calm down. Low magnesium is associated with poor sleep quality, difficulty falling asleep, and waking in the night. Evidence from a 2024 systematic review supports the benefit of magnesium supplementation for mild insomnia and anxiety. Taking magnesium glycinate or magnesium threonate in the evening, rather than magnesium oxide (which has poor bioavailability), is better supported by the evidence if supplementation is the route you're considering — though this should be discussed with a healthcare provider if you're on other medications.

Exercise, sweat, and athletic magnesium losses

Exercise increases magnesium requirements — both through sweat losses and because magnesium is required for ATP production, the cellular energy currency used in every muscle contraction. People who train regularly, particularly at high intensity, have meaningfully higher magnesium needs than sedentary individuals. Persistent muscle cramps, slow recovery, or unexplained fatigue in an otherwise fit and active person should prompt a magnesium check alongside iron and vitamin D.