What Is Bioavailability?
Bioavailability refers to the proportion of a nutrient that enters systemic circulation and is available for use by the body. A supplement with 80% bioavailability delivers 4x more usable nutrient than one with 20% bioavailability at the same dose.
Why Form Matters More Than Dose
The most common mistake in supplement selection is focusing on total milligrams rather than the form. A 500mg magnesium oxide capsule (4% bioavailability) delivers approximately 20mg of usable magnesium, while a 200mg magnesium glycinate capsule (80% bioavailability) delivers approximately 160mg — 8x more from a lower dose.
Factors That Affect Bioavailability
Chemical form: Chelated minerals (bound to amino acids) absorb better than inorganic salts. Methylated B vitamins absorb better than synthetic forms.
Timing: Fat-soluble vitamins (A, D, E, K) require dietary fat for absorption. Taking them with a meal containing fat can increase absorption by 200-300%.
Nutrient interactions: Calcium and iron compete for absorption. Vitamin C enhances iron absorption by up to 67%. Vitamin D enhances calcium absorption.
Individual factors: Age, gut health, medications, and genetic variations in metabolic enzymes all affect individual bioavailability.
Bioavailability by Common Supplement
| Supplement | High Bioavailability Form | Low Bioavailability Form | Difference |
|---|---|---|---|
| Magnesium | Glycinate (~80%) | Oxide (~4%) | 20x |
| Iron | Bisglycinate (~90%) | Ferrous sulfate (~10%) | 9x |
| Zinc | Picolinate (~60%) | Oxide (~15%) | 4x |
| CoQ10 | Ubiquinol (~95%) | Ubiquinone (~40%) | 2.4x |
| Curcumin | With piperine (~2000%) | Standard extract (~1%) | 20x |