Your kidneys are the safeguard.
Magnesium pills are usually safe for people with healthy kidneys. But when kidneys work at less than 30% of normal, they can't get rid of extra magnesium - and that can be dangerous. Understanding kidney function is key to magnesium safety.
Filtered by healthy kidneys daily
Healthy kidneys can handle per day
Kidney function threshold for danger
How healthy kidneys protect you.
Your kidneys are like super-smart filters. Every day, they clean about 2,400 mg of magnesium from your blood - then put most of it back, only excreting about 100 mg.
Three-Part Team
Your kidneys have three special parts: the first saves 10-25% of magnesium, the second does most work saving 65-70%, and the third makes tiny adjustments saving 3-7%.
Adaptive Response
When you have too much magnesium, healthy kidneys can change from saving almost all of it to getting rid of most of it. They can handle 50 times more than what you normally need!
When kidneys can't keep up.
Above 30% Function
Kidneys work extra hard to compensate, increasing excretion from 3-5% up to 15-20%. Most people are still safe at this stage with monitoring.
Below 30% Function - The Danger Zone
Kidneys can't keep up anymore. At 20% function, they can only filter 800 mg instead of 2,400 mg. Even if they try their hardest, they can only excrete 160 mg a day.
Below 10% Function - Critical
About 10-15% of hospitalized patients with very sick kidneys get too much magnesium. Even regular antacids or laxatives with magnesium can make them very sick in just a few days.
Symptoms from mild to dangerous.
Early Signs (2.5-4.0 mg/dL)
Weakness, fatigue, nausea, dizziness, facial flushing. Low blood pressure that medicine can't fix is a critical early warning.
Medium Warning (7-12 mg/dL)
The knee-tap test stops working, muscles get very weak, feeling very sleepy, heart beats too slowly, heart tests show problems.
Emergency (>12 mg/dL)
Complete muscle paralysis, may stop breathing on their own, heart can stop working right and may even stop beating.
Safe dosing by kidney function.
Healthy Kidneys
Government recommends up to 350 mg from supplements daily. Most people take 200-400 mg safely. Can handle 50x normal without issues.
Kidney Function 15-59%
Can still take magnesium with doctor supervision. Start with 200-300 mg daily. Blood tests every 2-4 weeks.
Kidney Function <15%
Usually shouldn't take magnesium pills. If needed, only 50-100 mg with weekly blood tests. Just 1,000-1,650 mg can cause severe illness.
Important: 93% of people needing emergency treatment for too much magnesium were elderly. As we age, kidneys work less efficiently - often without knowing it without a test.
Know your kidney function first.
Magnesium pills are safe for most people, but kidney function matters. People with sick kidneys are 10 times more likely to get sick from magnesium. Before taking magnesium pills, especially if you're over 65, ask your doctor to check kidney function. If someone loses their knee-jerk reflex, they need help right away.