Most men get around 60 percent of the magnesium they need from food. The rest they're not getting. And unlike iron deficiency or vitamin D deficiency, there's no obvious symptom that points directly to it.
That's what makes it so easy to miss.
Why deficiency is so common
Three reasons. First, modern diets are low in the foods that contain it: leafy greens, nuts, seeds, whole grains. Most men aren't eating enough of those. Second, soil depletion means the food that does contain magnesium has less of it than it did fifty years ago. You'd need to eat significantly more spinach today to get the same magnesium content. Third, anything that stresses the body depletes it faster. Alcohol. Caffeine. Hard training. Chronic stress. All of them increase magnesium excretion.
Put those three things together and you've got a large proportion of men running low.
The symptoms you'd never attribute to it
Fatigue that sleep doesn't fix. Muscle cramps, particularly at night. Difficulty staying asleep. Low mood with no clear cause. Tension headaches. A general sense of being on edge. None of those scream magnesium. They scream stress, or overtraining, or just getting older.
That's the problem. The symptoms are vague enough that most men never investigate the cause.
Why blood tests miss it
Standard blood tests measure magnesium in the blood. Only about one percent of the body's magnesium is in the blood. The rest is in cells and bones. You can have normal blood magnesium and still be functionally deficient in the tissues that need it most.
If the symptoms fit, it's worth supplementing regardless of what a blood test says.
Related reading: Does magnesium actually help with sleep?, Does magnesium boost testosterone?