Magnesium
Also known as: Mg, Serum Magnesium
What Does Magnesium Measure?
Magnesium (Mg) is an essential mineral measured in the blood serum or plasma, reflecting the amount of magnesium circulating in your bloodstream. The test evaluates whether your body has adequate levels of this vital nutrient, which is involved in over 300 enzymatic reactions throughout the body. However, it's important to note that only about 1% of the body's total magnesium is found in the blood — the vast majority is stored in bones and soft tissues — so serum magnesium may not always capture the full picture of your body's magnesium status.
Why Does Magnesium Matter?
Magnesium plays a critical role in muscle and nerve function, blood sugar regulation, blood pressure control, protein synthesis, and bone development. It is also essential for converting food into energy and synthesizing DNA and RNA. Low magnesium levels (hypomagnesemia) are linked to cardiovascular disease, type 2 diabetes, migraines, osteoporosis, and anxiety, while high levels (hypermagnesemia) — though less common — can impair neuromuscular function and cardiac rhythm. Because magnesium deficiency is widespread and often goes undetected, monitoring serum magnesium is valuable for assessing overall metabolic and cardiovascular health.
Normal Ranges
Males
1.7–2.2 mg/dL (0.70–0.91 mmol/L)
Females
1.7–2.2 mg/dL (0.70–0.91 mmol/L)
Children
1.7–2.1 mg/dL (0.70–0.86 mmol/L); varies by age
Causes of High Levels
- Kidney failure or chronic kidney disease (impaired magnesium excretion)
- Excessive use of magnesium-containing antacids or laxatives (e.g., Milk of Magnesia)
- Adrenal insufficiency (Addison's disease) reducing renal excretion
- Hypothyroidism slowing metabolic clearance of magnesium
- Overuse of magnesium supplements or intravenous magnesium therapy
- Severe dehydration causing hemoconcentration of serum minerals
Causes of Low Levels
- Poor dietary intake — diets low in green vegetables, nuts, seeds, and whole grains
- Chronic alcohol use causing increased urinary magnesium excretion
- Type 2 diabetes and insulin resistance promoting renal magnesium wasting
How to Improve Your Magnesium
Diet
- Eat dark leafy greens daily — spinach, Swiss chard, and kale are among the richest food sources (1 cup cooked spinach provides ~157 mg)
- Include pumpkin seeds and sunflower seeds as snacks (1 oz pumpkin seeds provides ~168 mg of magnesium)
- Consume legumes such as black beans, lentils, and chickpeas regularly (1 cup black beans provides ~120 mg)
- Choose whole grains over refined grains — brown rice, quinoa, and oats retain significantly more magnesium
- Eat dark chocolate (70% cocoa or higher) in moderation — 1 oz provides approximately 64 mg of magnesium
Supplements
- Magnesium glycinate 200–400 mg daily — highly bioavailable and gentle on the digestive tract, ideal for general supplementation and sleep support
- Magnesium citrate 200–400 mg daily — well-absorbed and commonly used; may have mild laxative effects at higher doses
- Magnesium malate 200–400 mg daily — beneficial for muscle function and fatigue; often recommended for fibromyalgia
- Magnesium threonate 1,500–2,000 mg daily (providing ~144 mg elemental Mg) — shown to cross the blood-brain barrier, potentially supporting cognitive function
Related Biomarkers
Frequently Asked Questions
Can I be magnesium deficient even if my blood test is normal?
Yes, this is called 'subclinical' or 'latent' magnesium deficiency. Because only about 1% of your body's magnesium is in the blood, serum levels can appear normal even when your bones and cells are depleted. Some clinicians use a magnesium loading test or red blood cell (RBC) magnesium test for a more accurate assessment of total body magnesium status.
What are the symptoms of low magnesium?
Symptoms of low magnesium (hypomagnesemia) include muscle cramps, twitching, tremors, fatigue, irritability, anxiety, irregular heartbeat (arrhythmia), high blood pressure, insomnia, and headaches or migraines. Severe deficiency can cause numbness, seizures, and abnormal heart rhythms. Many people have mild deficiency with subtle symptoms that are often attributed to other causes.
What is the best form of magnesium supplement to take?
The best form depends on your goal. Magnesium glycinate is the top choice for most people due to its high absorption and minimal digestive side effects. Magnesium citrate is a good general-purpose option. Magnesium threonate is preferred for brain health. Magnesium malate may be better for muscle pain and energy. Magnesium oxide, despite being widely available and cheap, has very poor absorption and is not recommended for correcting deficiency.
Can too much magnesium be harmful?
In healthy individuals with normal kidney function, excess dietary magnesium is safely excreted in urine and rarely causes problems. However, very high doses from supplements can cause nausea, diarrhea, and abdominal cramping. Severe hypermagnesemia (very high blood magnesium) is typically only seen in people with kidney failure or those receiving intravenous magnesium, and can cause dangerously low blood pressure, difficulty breathing, and cardiac arrest. The tolerable upper intake level for supplemental magnesium is 350 mg/day for adults.