Magnesium Intake Calculator

How Magnesium Intake Is Calculated

Magnesium is involved in over 300 enzymatic reactions, including energy production, muscle function, and protein synthesis. How much you need depends on age, sex, and life stage.

Recommended Dietary Allowances (RDA) for Magnesium, from the NIH:

What the calculator does not add. Some calculators raise the target 10 to 20% for exercise or add a fixed amount for stress. No guideline does either. Sweat does carry some magnesium, and hard training raises urinary losses a little, but no guideline raises the allowance for it. Someone eating to match their training takes in more magnesium with the extra food. The stress claim rests on small studies of urinary magnesium, and nobody has turned it into a number.

Upper Tolerable Limit: 350 mg a day from supplements for anyone 9 and over (65 mg for children 1 to 3 and 110 mg for 4 to 8). This is the number people get wrong most often. It applies to supplemental magnesium only. Magnesium from food has no upper limit, because the gut absorbs a smaller fraction when intake is high and the kidneys clear the rest. So a 420 mg target is perfectly reachable through food, while a 420 mg supplement is not a good idea. Too much supplemental magnesium causes diarrhea first, which is also why magnesium citrate is sold as a laxative.

Magnesium in Common Foods (mg per 100 g):

• Pumpkin seeds: 550 mg (156 mg per ounce)
• Almonds: 270 mg (77 mg per ounce)
• Dark chocolate, 70%+: 228 mg
• Spinach, cooked: 87 mg (157 mg per cooked cup)
• Black beans: 70 mg
• Avocado: 29 mg
• Banana: 27 mg

Worked Example:

A 35-year-old woman (RDA = 320 mg/day):

• 30g almonds = 81 mg
• 100g spinach = 87 mg
• 100g black beans = 70 mg
• 1 medium banana = 33 mg
• Total: 271 mg, so about 49 mg short. A handful of pumpkin seeds closes it.

Note how easily food gets you there. That is the general case: magnesium deficiency severe enough to show on a blood test is uncommon in people eating a varied diet, and the far more common situation is a diet heavy in refined grains, where most of the magnesium is milled out.

Deficiency Signs: muscle cramps, fatigue, irregular heartbeat, anxiety, poor sleep. These are all non-specific, which is the problem. A serum magnesium test is also a poor guide, since less than 1% of body magnesium is in the blood and the body defends that level hard. If you suspect a real deficiency, that is a conversation with a doctor rather than a supplement bought on a hunch.