Magnesium drops below normal levels through two main routes: your body loses too much of it (through urine or your digestive tract), or you don’t absorb enough from food. A normal blood magnesium level falls between 1.7 and 2.2 mg/dL, and nearly half of all Americans don’t get enough magnesium from their diet to begin with. From there, medications, medical conditions, and lifestyle factors can push levels even lower.
Not Enough Coming In
The simplest explanation is also the most common. An analysis of NHANES data from 2013 to 2016 found that 48% of Americans consume less magnesium from food and beverages than the estimated average requirement. Adults over 71 and teenagers of both sexes are the most likely to fall short. Magnesium-rich foods like leafy greens, nuts, seeds, and whole grains have been partly replaced by processed foods that contain very little. Research has also shown that the magnesium content of cereal grains themselves has declined over time due to changes in agricultural practices and soil quality.
A mild dietary shortfall might not cause obvious symptoms for a while. Your body stores most of its magnesium in bone and muscle tissue, and it can draw on those reserves to keep blood levels stable. But if intake stays low for months or years, those reserves gradually thin out, and deficiency symptoms start to appear: muscle cramps, fatigue, irritability, and poor sleep.
Medications That Drain Magnesium
Several widely prescribed drugs force the kidneys to flush out more magnesium than normal. Diuretics (water pills) are among the most common culprits. Both loop diuretics and thiazide diuretics impair the kidneys’ ability to hold onto magnesium, and studies in elderly patients have confirmed increased magnesium loss in urine during long-term use of either type.
Acid-blocking drugs called proton pump inhibitors (PPIs) are another major cause. The FDA has warned that PPIs taken for at least three months can lower magnesium levels, though most cases appear after a year of continuous use. The consequences can be serious: reported complications include abnormal heart rhythms, seizures, and severe muscle spasms. In most affected patients, fixing the problem required both magnesium supplementation and stopping the PPI. If you take a PPI alongside a diuretic, the risk compounds, and periodic magnesium monitoring is recommended.
Other medications linked to magnesium wasting include certain antibiotics, some chemotherapy drugs, and immunosuppressants used after organ transplants. If you’ve started a new medication and notice muscle twitching, cramping, or unusual fatigue, low magnesium is worth investigating.
Digestive Conditions That Block Absorption
Your small intestine is where most magnesium absorption happens, so anything that damages or inflames that lining can cause a deficit. Celiac disease is a clear example. The immune reaction to gluten flattens the tiny finger-like projections (villi) that line the intestine, dramatically reducing the surface area available to absorb nutrients. Untreated celiac disease can lead to severe malabsorption of magnesium along with iron, calcium, and several vitamins.
Crohn’s disease, particularly when it affects the small intestine, creates a similar problem through chronic inflammation. Chronic diarrhea from any cause, including irritable bowel syndrome, infections, or surgical removal of part of the intestine, speeds food through the gut too quickly for magnesium to be fully absorbed. Even prolonged vomiting can deplete magnesium, since digestive fluids contain meaningful amounts of it.
How Alcohol Depletes Magnesium
Heavy drinking attacks magnesium levels from multiple directions at once. Alcohol increases urinary magnesium loss, pulls magnesium out of tissues, and often replaces nutrient-dense meals with empty calories. In one study of patients with alcohol use disorder, over 55% had low serum magnesium. Even among heavy drinkers who hadn’t yet developed a clinical disorder, nearly a third showed low levels.
Chronic alcohol use has been shown to deplete total body magnesium stores, not just the amount circulating in blood. Animal research confirms that long-term alcohol exposure impairs the body’s magnesium transport systems in tissues, making it harder to maintain normal levels even when dietary intake is adequate. This is one reason magnesium replacement is a standard part of treatment during alcohol withdrawal.
Kidney Problems and Magnesium Wasting
Your kidneys normally reclaim about 95% of the magnesium they filter from blood. When kidney function is disrupted, that reabsorption rate drops and magnesium pours out in urine. This can happen with chronic kidney disease, but it also occurs in more subtle situations. Poorly controlled diabetes, for instance, causes excess glucose to spill into urine, and magnesium follows it out. High blood sugar also directly impairs the kidney’s magnesium-reclaiming machinery.
Certain genetic conditions cause the kidneys to waste magnesium from birth, though these are rare. More commonly, temporary kidney stress from illness, dehydration, or medication changes can tip someone who’s already borderline into deficiency.
Why Standard Blood Tests Can Miss It
One frustrating aspect of magnesium deficiency is that it’s easy to overlook. The standard blood test measures serum magnesium, the amount dissolved in your blood plasma. But only about 1% of your body’s total magnesium is found in the bloodstream. The rest, over 99%, sits in bones, muscles, and soft tissues. This means your blood level can look normal even when your overall stores are significantly depleted.
There is currently no simple, rapid, and accurate test to measure total body magnesium status. Your body works hard to keep serum levels stable by pulling from bone and tissue reserves, so by the time a standard blood test shows a low number, the deficit has usually been building for a while. Some clinicians use a 24-hour urine collection or a magnesium loading test (measuring how much your body retains after a dose) to get a better picture, but these are less commonly ordered.
Because blood testing is imperfect, doctors sometimes treat suspected magnesium deficiency based on symptoms and risk factors rather than waiting for a definitively low lab result. If you take PPIs or diuretics, drink heavily, have a digestive condition, or eat a heavily processed diet, you’re at higher risk regardless of what a single blood draw shows.
How Deficiency Builds Over Time
Magnesium deficiency doesn’t happen overnight. It develops gradually because there is little rapid exchange between the magnesium circulating in your blood and the much larger stores locked in bone and cells. A small deficit, from a week of poor eating or a bout of diarrhea, is easily corrected. But when the cause is ongoing, like a daily medication or an untreated digestive condition, the deficit compounds month after month.
Early signs tend to be vague: loss of appetite, nausea, fatigue, and general weakness. As levels drop further, muscle cramps, numbness, tingling, and abnormal heart rhythms can develop. Severe magnesium depletion also drags down calcium and potassium levels, because magnesium is needed for the body to regulate those minerals properly. This is why low magnesium sometimes only comes to light after a doctor notices that calcium or potassium won’t respond to supplementation.