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The cheapest option, but you get what you pay for. Magnesium oxide has the worst bioavailability of any common form -- only 4% is absorbed. The 400mg label dose is misleading.
Despite USP verification and extremely low cost, the fundamentally poor bioavailability of magnesium oxide means you are not getting what the label promises. The formulation score is the lowest in the category because the form itself undermines the purpose. No hype penalty because Nature Made does not overclaim -- but the product is still evidence-weak for magnesium supplementation goals.
Magnesium oxide provides 400mg elemental magnesium per tablet, but bioavailability studies consistently show only 4-5% absorption, meaning you effectively absorb approximately 16-20mg per dose. Comparative studies show magnesium glycinate, citrate, and threonate are all significantly better absorbed. Magnesium oxide does have evidence as an osmotic laxative, but that is not typically the intent of supplementation.
| Ingredient | Dose | Verdict |
|---|---|---|
| Magnesium Oxide | 400mg elemental | Underdosed |
Why the true cost is higher
This product has 1 underdosed and 0 unknown-dose ingredients. To actually get clinically effective doses, you would need approximately 3 servings per day -- making your real cost $0.15 per effective dose instead of the listed $0.05.
Only 4-5% bioavailability -- effectively delivers ~16mg of absorbable magnesium. Often causes loose stools due to osmotic effect. The 400mg label claim is technically accurate but functionally misleading. Better forms exist at modestly higher prices.
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