Low magnesium is most commonly caused by not getting enough from food, losing too much through your kidneys, or taking medications that interfere with absorption. Adults need between 310 and 420 mg of magnesium daily depending on age and sex, and many people fall short. Below that threshold, a combination of dietary gaps, medications, alcohol use, and certain health conditions can push your levels into deficiency.
How Much You Need and Where the Gaps Are
Men aged 19 to 30 need about 400 mg of magnesium per day, rising to 420 mg after age 31. Women in the same age ranges need 310 mg and 320 mg respectively. Pregnant individuals need 350 to 400 mg depending on age. These numbers come from the National Academies of Sciences, Engineering, and Medicine, and they represent the amount that covers the needs of most healthy people.
The problem is that magnesium is concentrated in foods many people don’t eat enough of: dark leafy greens, nuts, seeds, beans, and whole grains. A diet heavy in processed foods strips away much of the magnesium that was present in the original ingredients. Refined grains, for example, lose most of their magnesium during processing. If your diet leans toward white bread, packaged snacks, and fast food, you’re likely coming up short without realizing it.
Certain compounds in food also reduce how much magnesium your body actually absorbs. Phytic acid, found in whole grains, legumes, and seeds, binds to magnesium in your gut and prevents it from entering your bloodstream. Research in animal models shows this effect is dose-dependent: the more phytic acid in a meal, the less magnesium your body retains. Oxalic acid in foods like spinach and rhubarb does something similar. This doesn’t mean you should avoid these foods, since they’re nutritious in other ways, but it does mean the magnesium listed on a nutrition label isn’t the same as the magnesium your body actually uses.
Medications That Drain Magnesium
Several widely prescribed medications are known to lower magnesium levels over time. The two biggest culprits are acid-blocking drugs and water pills.
Proton pump inhibitors (PPIs), commonly taken for acid reflux and ulcers, interfere with magnesium absorption in a specific way. Your intestines absorb magnesium through specialized channels in the gut lining. These channels work best when the chemical environment in your intestine is within a certain range. PPIs change the acidity of the gut, which reduces the ability of those channels to grab onto magnesium molecules. The effect builds gradually. Most cases of PPI-related magnesium depletion show up after months or years of continuous use, which is why short courses are less of a concern.
Diuretics (water pills) used for high blood pressure and heart failure cause your kidneys to flush out more fluid, and magnesium goes with it. Loop diuretics and thiazide diuretics are particularly known for this effect. If you take one of these medications and notice muscle cramps or fatigue, low magnesium is worth investigating.
Other medications linked to magnesium loss include certain antibiotics, some anti-fungal drugs, and immunosuppressants used after organ transplants. If you’re on long-term medication of any kind and experiencing symptoms of low magnesium, your prescriber can check your levels.
How Alcohol Pushes Magnesium Out
Alcohol is one of the most potent triggers for magnesium loss. A study published in the Journal of Clinical Investigation found that a single dose of alcohol increased urinary magnesium excretion by an average of 167%, with some subjects losing up to 357% more magnesium than normal. This spike happened quickly and consistently in both alcoholic and non-alcoholic subjects.
The mechanism appears to be a direct effect on the kidneys. Normally, your kidneys reabsorb most of the magnesium that passes through them, sending it back into your bloodstream. Alcohol, or one of its breakdown products, disrupts this reabsorption process. The magnesium passes straight through into your urine instead. This effect is independent of how much urine you’re producing, so it’s not simply that you’re peeing more. The kidneys are genuinely letting magnesium slip away that they would normally reclaim.
For heavy or chronic drinkers, this creates a compounding problem. Magnesium stores drop, the body can’t replenish them fast enough, and the next round of drinking depletes them further. This is one reason magnesium deficiency is extremely common in people with alcohol use disorder.
Health Conditions That Lower Magnesium
Several medical conditions make it harder for your body to hold onto magnesium, even if your diet is adequate.
- Digestive disorders: Crohn’s disease, celiac disease, and chronic diarrhea all reduce the amount of magnesium your gut can absorb. Any condition that damages the intestinal lining or speeds food through the digestive tract limits absorption time.
- Type 2 diabetes: High blood sugar causes the kidneys to filter more glucose, and magnesium gets swept out along with it. People with poorly controlled diabetes are at especially high risk.
- Kidney disease: Damaged kidneys lose their ability to regulate magnesium properly. Depending on the stage and type of kidney disease, this can go in either direction, but magnesium wasting is common in earlier stages.
- Older age: Magnesium absorption in the gut decreases with age, while kidney excretion tends to increase. Older adults are also more likely to take medications that deplete magnesium, creating a triple disadvantage.
What Low Magnesium Feels Like
Mild magnesium deficiency often starts with symptoms that are easy to dismiss: fatigue, general weakness, and muscle cramps or spasms. You might notice tingling or numbness in your hands and feet, or a feeling of tightness in your muscles that doesn’t seem related to exercise. Tremors and abnormal eye movements can also appear early on.
If the deficiency worsens, the symptoms become more serious. Severe magnesium depletion can cause abnormal heart rhythms, seizures, and delirium. These are medical emergencies and typically only happen when levels drop significantly below normal. The normal blood range for magnesium is 1.6 to 2.6 mg/dL, and severe symptoms usually appear at the lower end of that range or below it.
One tricky aspect of magnesium deficiency is that it tends to drag other minerals down with it. Low magnesium makes it harder for your body to maintain normal potassium and calcium levels, so symptoms of those deficiencies can overlap and compound the problem.
Why Standard Blood Tests Can Miss It
Here’s something most people don’t realize: a normal magnesium result on a standard blood test doesn’t necessarily mean your magnesium levels are fine. The typical test measures magnesium in your blood serum, but only about 1% of your body’s magnesium is in your blood. The rest is stored in your bones and tissues. When blood levels start to drop, your body pulls magnesium out of your bones to keep blood levels stable. This means your serum test can look perfectly normal while your actual magnesium stores are depleted.
A more sensitive option is the RBC magnesium test, which measures magnesium inside your red blood cells rather than in the liquid portion of your blood. This gives a better picture of what’s actually stored in your cells. If you suspect low magnesium but your standard blood test came back normal, asking for an RBC magnesium test is a reasonable next step.