What Is Bioavailability — and Why It Matters More Than Dosage

May 3, 2025

You might think a supplement’s effectiveness is all about the number on the label. But the truth is: your body can only use what it actually absorbs. That’s where bioavailability comes in.

What is Bioavailability?

Bioavailability refers to how much of a nutrient is actually absorbed into the bloodstream and made available to cells. You might take 100 mg of a vitamin, but if your body only absorbs 25 mg, the bioavailability is just 25%.

This matters — a lot. Because no matter how high the dose, if your body can’t absorb it, it won’t benefit you.

What Affects Bioavailability?

The chemical form (organic vs. inorganic)
Presence of natural cofactors (fats, enzymes, amino acids)
Digestive health and gut flora
Your age, stress levels, and metabolism

For example, magnesium oxide has a bioavailability of just ~4%.

Why Bigger Doses ≠ Better

Many assume a higher number on the bottle means greater benefit. Not necessarily. A 500 mg synthetic vitamin might deliver less than a 100 mg natural source.

Unabsorbed nutrients pass through the system unused
Some may even burden the liver or kidneys
High doses of isolated nutrients can spike, then crash

Vitamin D2 and D3 are great examples. D3 (from lichen) is far better absorbed than D2 — even at equal dosages.

Natural Forms Offer Synergy

When nutrients come from natural sources — such as berries, seaweed, seeds, or plants — they arrive in the body not as isolated chemicals, but as part of a complex biological system. These forms include natural cofactors that enhance absorption and effectiveness.

Why whole-food-based nutrients are better absorbed:

They include supporting compounds: enzymes, amino acids, lipids, flavonoids — all of which help the body recognize and utilize the nutrients.
Naturally bio-compatible: natural forms follow familiar metabolic pathways, unlike synthetic forms that may require extra processing.
Solubility and pH compatibility: plant-based nutrients typically dissolve and absorb more efficiently in the digestive tract.

Natural vs. Synthetic: A Clear Difference

Vitamin C: Natural vitamin C from acerola or rosehip offers 70–80% bioavailability due to the presence of bioflavonoids, organic acids, and enzymes. It’s absorbed more gradually and retained longer in tissues, providing a sustained antioxidant effect.
In contrast, synthetic ascorbic acid is absorbed quickly but has a much lower retention rate, with only 15–30% bioavailability, especially at high doses — the excess is rapidly excreted.
Magnesium: Natural magnesium from marine sources (like algae) delivers 70–90% bioavailability. These forms are gentle on the gut and efficiently absorbed at the cellular level.
Synthetic magnesium oxide, however, has bioavailability of only 4–5%. It is poorly absorbed and often causes gastrointestinal discomfort or a laxative effect.
Calcium: Derived from marine algae calcium offers 70–80% bioavailability, while synthetic calcium carbonate provides only 20–30%.
Vitamin E: The natural d-alpha-tocopherol form is 1.7 to 2 times more bioavailable than the synthetic dl-alpha version.
Omega-7: Natural omega-7 from sea buckthorn comes with built-in antioxidants like vitamins A and E, enhancing stability and absorption to 60–70%, whereas isolated synthetic omega fatty acids are absorbed at around 30%.