How Much Magnesium Adults Need
The NIH Office of Dietary Supplements sets the magnesium RDA at 400–420 mg/day for men and 310–320 mg/day for women [1]. Magnesium supports hundreds of enzyme reactions — energy, muscle and nerve function, and more — yet many people don't reach the recommended intake from diet alone.
Who Is Most at Risk
NIH identifies several groups more likely to have inadequate magnesium [1]:
- People with GI conditions — Crohn's disease and celiac disease impair absorption and increase losses.
- People with type 2 diabetes — higher urinary magnesium losses.
- People with alcohol dependence — poor intake plus increased excretion.
- Older adults — lower intake and reduced absorption with age.
Why Blood Tests Can Miss It
Less than 1% of the body's magnesium circulates in blood; most sits in bone and soft tissue. That means a standard serum magnesium test can read normal even when whole-body stores are low. There's no perfect everyday test, so clinicians weigh intake, risk factors, and symptoms together.
Common Signs (and Why They're Non-Specific)
Low magnesium can show up as muscle cramps, fatigue, poor sleep, or irritability — but these overlap with many other causes, so symptoms alone don't confirm a deficiency. Severe depletion is a medical issue that needs clinical evaluation.
Food First, Then Form
Magnesium-rich foods include leafy greens, nuts, seeds, legumes, and whole grains. If you supplement, the form strongly affects absorption (see Magnesium Types Compared) — and some forms are gentler on the gut than others. If you take medications, note that magnesium can interact with several (see Supplements and Medications).