Low magnesium has several common causes, but the biggest one is straightforward: not getting enough from food. Nearly half of Americans fall short of the recommended daily intake. Beyond diet, medications, digestive conditions, alcohol use, diabetes, and kidney problems can all drain magnesium levels or block absorption. Adults need between 310 and 420 mg of magnesium per day, depending on age and sex.
Not Enough Magnesium in Your Diet
This is the most widespread cause. An analysis of national nutrition survey data from 2013 to 2016 found that 48% of Americans of all ages consume less magnesium from food and beverages than they need. Men over 71 and teenagers of both sexes are the most likely to fall short.
A big reason is how food gets processed. Refining grains strips away the germ and bran, which are the parts richest in magnesium. White flour, white rice, and other refined staples contain significantly less than their whole-grain versions. If your diet leans heavily on processed foods and light on nuts, seeds, leafy greens, and legumes, your intake is likely below the target. For reference, adult men need 400 to 420 mg per day and adult women need 310 to 320 mg, with slightly higher needs during pregnancy.
Certain compounds in food can also reduce how much magnesium your body actually absorbs. Phytates, found in whole grains, seeds, legumes, and some nuts, bind to magnesium in the digestive tract and make it less available. This doesn’t mean you should avoid those foods (they’re excellent sources of magnesium overall), but it helps explain why absorption is never 100% efficient.
Medications That Deplete Magnesium
Several widely prescribed drug classes push magnesium levels down, often by changing how your kidneys handle it. The most common culprits are loop and thiazide diuretics (water pills), which increase urinary magnesium loss. These are among the most frequently prescribed blood pressure medications in the world, so this is a significant cause at a population level.
Proton pump inhibitors, the heartburn and acid reflux drugs many people take daily for months or years, also lower magnesium. The mechanism is different from diuretics. Rather than flushing magnesium through the kidneys, PPIs appear to impair absorption in the gut. Other medications linked to magnesium wasting include certain antibiotics and platinum-based chemotherapy drugs. If you take any of these long-term, your magnesium levels may drift downward gradually enough that you don’t notice symptoms until the deficit is substantial.
Digestive Conditions That Block Absorption
Magnesium is absorbed primarily in the small intestine, so any condition that damages or disrupts that part of the gut can cause deficiency. Crohn’s disease, ulcerative colitis, celiac disease, Whipple’s disease, and short bowel syndrome are all associated with low magnesium. Chronic diarrhea from any cause speeds food through the intestines too quickly for adequate absorption.
Conditions that cause fat malabsorption (steatorrhea) are especially problematic. When fat isn’t properly absorbed, it binds with magnesium in the intestine to form insoluble compounds called magnesium soaps. These pass through without being absorbed. A lower-fat diet can actually improve magnesium balance in people with these conditions.
There is also a rare inherited form of magnesium malabsorption caused by a mutation in the TRPM6 gene, which codes for an ion channel in the intestinal lining. In affected infants, the fraction of dietary magnesium absorbed drops to about 35%, compared to roughly 70% in healthy infants. This can cause seizures and dangerously low calcium levels early in life.
Alcohol Use
Chronic heavy drinking is one of the most reliable predictors of low magnesium. The primary mechanism is the kidneys: people with alcohol use disorder excrete inappropriately high amounts of magnesium in their urine, even when their blood levels are already low. Normally, the kidneys conserve magnesium when levels drop, but alcohol disrupts this feedback loop.
Poor nutritional intake compounds the problem. Heavy drinkers often replace food calories with alcohol calories, which contain no magnesium. The combined effect of increased loss and decreased intake makes magnesium deficiency common in this group.
Diabetes and Blood Sugar Problems
Type 2 diabetes is strongly linked to low magnesium. Studies report that anywhere from 14% to 48% of people with diabetes have levels below normal, depending on the population studied. Multiple mechanisms work together to cause this.
When blood sugar runs high, the kidneys filter out excess glucose into the urine, pulling water and magnesium along with it. This process, called osmotic diuresis, increases magnesium loss every time blood sugar spikes. Insulin resistance adds another layer: insulin normally helps move magnesium into cells, so when cells stop responding to insulin properly, more magnesium stays outside cells and gets flushed by the kidneys. The kidneys themselves also become less efficient at reclaiming magnesium from urine when insulin signaling is impaired. These overlapping losses make magnesium deficiency both a consequence and a potential accelerator of diabetes, since magnesium plays a role in insulin signaling.
Kidney Problems
Your kidneys are the main regulators of magnesium balance. They filter magnesium out of the blood and then reabsorb most of it before it reaches the urine. When this reabsorption process breaks down, you lose magnesium faster than you can replace it through food.
Clinicians can measure this directly: if more than 2% of filtered magnesium ends up in the urine in someone with otherwise normal kidney function, the kidneys themselves are the problem. This can happen because of medications (diuretics, certain antibiotics, chemotherapy), genetic conditions, or damage from chronic kidney disease. Inherited conditions like Gitelman syndrome cause lifelong magnesium wasting through the kidneys, requiring ongoing supplementation.
Genetic Conditions
Several rare inherited disorders cause chronic low magnesium from birth or early childhood. Mutations in the TRPM6 gene impair magnesium absorption in the intestine. Mutations in CNNM2, a gene active in the kidney’s filtering tubes, disrupt the kidney’s ability to hold onto magnesium. Patients with CNNM2 mutations can develop seizures, low magnesium, and impaired brain development. These conditions are uncommon but important to recognize because they require lifelong magnesium replacement and don’t respond to dietary changes alone.
How Low Magnesium Is Detected
A standard blood test measures serum magnesium. The normal range for adults is 1.7 to 2.3 mg/dL. Levels below that range confirm deficiency, but there’s an important caveat: only about 1% of your body’s magnesium circulates in the blood. The rest is stored in bones and inside cells. This means your blood level can look normal even when your total body stores are significantly depleted. A low blood reading reliably indicates deficiency, but a normal reading doesn’t rule it out.
Symptoms of deficiency typically don’t appear until levels drop to 1.0 mg/dL or lower, which represents severe depletion. Mild to moderate deficiency can exist for a long time without obvious signs.
Symptoms to Recognize
Early magnesium deficiency often causes muscle cramps, twitching, fatigue, and weakness. As levels drop further, you may experience numbness or tingling, especially in the hands and feet. Nausea and loss of appetite are common.
Severe deficiency affects the heart and nervous system. It can cause abnormal heart rhythms, personality changes, and involuntary muscle spasms. One hallmark sign is a spasm of the hand and wrist when blood flow to the arm is briefly restricted, where the fingers draw together in a distinctive posture. Tapping near the jaw can trigger facial muscle twitching, another sign of the heightened nerve excitability that comes with very low magnesium. Low magnesium also tends to drag down calcium and potassium levels, since magnesium is involved in regulating both. This means symptoms of those deficiencies, like more severe cramping and heart rhythm issues, can layer on top.