I’m trying to find the prevalence of magnesium deficiency in the US. This USDA site says that 57% of the US population does not meet the RDA for dietary intake of magnesium. But remember, when intake is low, we absorb more from food and excrete less:

“Symptomatic magnesium deficiency due to low dietary intake in otherwise-healthy people is uncommon because the kidneys limit urinary excretion of this mineral.”

How is it then that the doctor on this site says, “80% of all Americans are magnesium deficient.” Deficiency is serious business. A magnesium deficiency is a defined state (serum and tolerance tests) accompanied by overt symptoms such as nausea, vomiting, hallucinations, rapid heartbeat, delirium, and death. Suboptimal intakes of magnesium or magnesium inadequacy are not as serious. A doctor is trained to use the word “deficiency” carefully. So, 80% are deficient? I don’t see it, do you?

We don’t need much: 320 mg for a woman, 420 mg for a man. And it’s in lots of foods:

Where do statistics like ‘80% deficient’ come from?