If your serum magnesium is in the normal range, you might conclude that you’re getting enough of this mineral.
Sweet, I don’t have hypomagnesemia. I guess I’m not low on magnesium!
That’s how most people think about electrolyte status. They believe the blood test tells all.
It doesn’t. For all the major electrolytes (including magnesium), normal blood levels merely suggest that the person has functional kidneys, isn’t suffering an acute illness, and isn’t taking electrolyte-depleting medications.
Serum electrolyte tests don’t accurately detect nutritional imbalances. Why? Because the body has built-in homeostatic mechanisms for maintaining electrolyte levels, even when you’re not getting enough of that electrolyte through diet. I’ll talk more about this later.
A nutritional deficiency may increase the risk of hypomagnesemia (low blood magnesium levels), but it’s rarely the sole cause. That’s why, despite widespread magnesium inadequacy, hypomagnesemia only affects about 2% of the population. It’s MUCH more common in intensive care patients (~50%) who tend to suffer heavy magnesium losses through the kidneys.
Think of hypomagnesemia as a state of emergency. It means some bodily system (a system that keeps magnesium levels up) isn’t working correctly, usually due to medications or illness.
Though it’s rare in healthy people, hypomagnesemia highlights the need for magnesium in our physiology. When serum levels drop, things go south in a hurry.
Why We Need Magnesium
Magnesium is required for over 300 enzymatic reactions in your body. I’m talking about reactions that promote DNA repair, muscle synthesis, energy production, bone formation, wound healing, you name it.
For instance, a molecule called MgATP2 complex (Magnesium ATP 2 complex) is required to produce the molecule which stores the energy that powers all living cells: ATP. Magnesium is also critical for structuring bones and teeth, which explains why magnesium deficiency is linked to osteoporosis risk.
Magnesium is also involved in all aspects of cardiac function: blood clotting, heart rhythm, calcification, blood vessel relaxation, and even the inflammatory response. As magnesium intakes go down, heart disease risk goes up.
Wait, isn’t magnesium an electrolyte too? That’s right. Like sodium, chloride, potassium, and calcium, magnesium conducts electricity to power your nervous system. Many of its roles, however, are unrelated to this function.
What Is Hypomagnesemia?
Hypomagnesemia is an electrolyte imbalance of low serum magnesium. Specifically, it’s when blood levels of this mineral fall below 1.46 mg/dL. (Normal magnesium levels are between 1.46 mg/dL and 2.68 mg/dL).
Hypomagnesemia symptoms can range from mild (slight tremors, muscle weakness) to moderate and severe (muscle cramps, arrhythmias, seizures, coma, delirium, death). I’ll provide a full symptom list shortly.
According to NIH StatPearls, hypomagnesemia occurs in:
- 2% in the general population
- 10% to 20% in hospitalized patients
- 50% to 60% in intensive care unit patients
- 30% to 80% in persons with alcohol use disorder
- 25% in outpatients with diabetes
Why is hypomagnesemia so rare in the general population? Because most people have a properly functioning system—a setup involving the kidneys, gut, bones, and various hormones—that maintains serum magnesium levels. If you’re critically ill or medicated, this homeostatic system is more likely to become disrupted.
The signs of hypomagnesemia typically manifest as neuromuscular symptoms, cardiovascular symptoms, or electrolyte disturbances. Let’s review these categories individually.
#1: Neuromuscular symptoms
- Muscle cramps
- Muscle spasms
- Muscle weakness
- Vertical nystagmus (involuntary vertical movement of the eye)
#2: Cardiovascular symptoms
- Heart arrhythmias (atrial fibrillation, ventricular arrhythmias)
- Premature systoles (increase in arterial pressure)
- Changes in heart function (as measured by an electrocardiogram)
- Cardiac ischemia (inadequate blood supply to the heart)
#3: Electrolyte and hormone disturbances
- Hypocalcemia (low serum calcium)
- Hypokalemia (low serum potassium)
- Hypoparathyroidism (low parathyroid hormone)
To identify hypomagnesemia, clinicians may run tests including:
- Serum magnesium or serum magnesium
- An electrocardiogram (a simple, non-invasive test that measures the electrical activity of the heart)
- A comprehensive metabolic panel (CMP) for markers of kidney function
- 24-hour urinary magnesium excretion
What Causes Hypomagnesemia?
Your body works hard to maintain serum magnesium levels. When they fall, you excrete less magnesium in urine and absorb more of it from food. Bone is also catabolized to provide any needed magnesium.
In other words, hypomagnesemia isn’t an everyday occurrence. It’s almost always the result of an illness, medical condition, or drugs.
Low magnesium intakes increase the risk of hypomagnesemia, but they’re seldom the sole cause. Your magnesium maintenance system makes sure of that.
I’ll talk more about dietary magnesium deficiency in the next section. Right now, let’s see what can bring blood levels down.
#1: Gut or urinary losses
We lose the bulk of our magnesium through feces and urine. Only a little is lost through sweat.
Because of this, illnesses that impair gut or kidney function are significant causes of hypomagnesemia. These include:
- Any condition involving diarrhea (Crohn’s, ulcerative colitis, IBS, acute gut illness)
- Acute pancreatitis and gastric bypass surgery (both impair magnesium uptake)
- Kidney disease
- Genetic kidney disorders like familial hypomagnesemia with hypercalciuria and nephrocalcinosis
Other conditions fall in this category, but those are the major ones.
#2: Refeeding syndrome
During periods of prolonged nutrient deprivation (an extended fast, say), the human body becomes depleted of magnesium, potassium, phosphorus, and sodium. That’s what happens when they’re not consumed.
When the fast is broken, the body wants to repair muscle, bone, and other tissues that need rebuilding. To do so, it rapidly pulls electrolytes out of the blood and into the tissues. The result is often hypokalemia (low potassium levels), hypophosphatemia (low phosphate levels), or hypomagnesemia.
The longer the fast, and the fewer electrolytes consumed during the fast, the greater the risk of refeeding syndrome. It’s unlikely with a 24 hour intermittent fast, but a 5 day water-only fast is a different story.
If you want to disturb electrolyte levels, drink lots of alcohol. Heavy alcohol consumption, it’s been shown, increases magnesium loss through urine and tissues. As blood alcohol levels rise, blood magnesium levels fall. Unsurprisingly, hypomagnesemia is very common in folks with alcoholic liver disease.
#4: Hungry bone syndrome
Hungry bone syndrome (HBS) refers to the excessive bone formation that often follows the removal of the parathyroid gland. Parathyroid hormone (PTH), by the way, is crucial for maintaining electrolyte levels and bone homeostasis.
The signature of HBS is hypocalcemia (low serum calcium), but it’s also associated with hypomagnesemia and hypophosphatemia. All of these minerals get sucked out of the serum to feed the hungry bones.
A variety of pharmaceuticals can deplete magnesium levels. These include:
- Diuretics (which increase urinary magnesium loss)
- Proton pump inhibitors (which decrease magnesium absorption)
- Aminoglycoside antibiotics
- Amphotericin B (an antifungal)
- Digitalis (used to treat certain heart conditions)
- Chemotherapy drugs
If you’re taking any of these meds, work with your doctor to monitor magnesium levels.
Hypomagnesemia vs. Magnesium Deficiency
Hypomagnesemia means low serum magnesium. It will show up on your blood electrolyte panel.
Magnesium deficiency means suboptimal magnesium intake. It will NOT consistently show up on a serum magnesium test. (Note: red blood cell magnesium is a better biomarker for magnesium status, but doctors don’t usually test for it).
Why won’t magnesium deficiency show up on a blood test? Because if you don’t consume enough magnesium, your body will tap its magnesium reserves: bone. From a survival perspective, blood magnesium is WAY more important than bone magnesium.
Low serum magnesium is a five-alarm fire. Basic functions (like the beating of your heart) are at risk. Low bone magnesium, however, won’t kill you right away. Osteoporosis and osteopenia are slow-burning, chronic conditions.
Beyond increasing fracture risk, where else might a magnesium deficiency manifest? In many places, but most notably in the heart.
A growing body of literature links magnesium insufficiency to various heart problems including:
- Hypertension (high blood pressure)
- Coronary artery disease
- Atrial fibrillation
- Increased stroke and heart attack risk
Let’s talk about managing your magnesium status now.
Optimizing Magnesium Status
Let’s assume that you don’t have hypomagnesemia. Your magnesium-retention system works well enough and you’re wondering how much magnesium you need to consume for optimal health.
Well, the RDA is 400-420 mg for adult men and 310-320 mg for adult women, but anthropological evidence suggests intakes around 600 mg per day are more commensurate with our biological needs. Since there’s little downside to extra magnesium, I lean towards the upper end of this range.
The best sources of dietary magnesium are leafy vegetables. Magnesium sits at the center of the chlorophyll molecule, so think green.
To determine your daily magnesium intake, log your meals in a nifty app called Cronometer. It spits out your magnesium consumption and you can take it from there.
Anecdotally, I’ve found that most people—even health-conscious people—still need about 200-300 mg more magnesium per day. With low-carb or ketogenic diets, it may be slightly more (again, anecdotal, not clinical). LMNT contains 60 mg of magnesium malate per stick to help move folks towards that goal.
One last point to remember is that dietary magnesium won’t necessarily prevent hypomagnesemia. Low serum magnesium generally indicates a medical condition, not a dietary deficiency.