Bioavailability Explained: How to Maximise Supplement Absorption

Introduction

You can take the highest quality supplement, but if your body doesn't absorb it, the benefit is minimal. Bioavailability refers to the proportion of an active ingredient that actually reaches your bloodstream (Rein et al., 2013) and is available to the body. Understanding this helps you make smarter choices and get more from your supplements.

What Is Bioavailability?

Bioavailability is the percentage of an active ingredient that is absorbed and reaches the systemic circulation. If you take 100 mg of magnesium and 30 mg reaches your bloodstream, the bioavailability is 30%.

Bioavailability depends on several factors:

• The chemical form of the active ingredient
• Whether you take it with food or on an empty stomach
• Interactions with other nutrients and medications
• Gut health
• Individual differences

Factors Affecting Absorption

1. Chemical Form

The same mineral in different forms absorbs very differently.

Magnesium example:

Iron example:

• Iron bisglycinate — good absorption, gentle on stomach
• Ferrous sulfate — cheaper, but more digestive side effects
• Iron carbonate — low bioavailability

2. Food and Timing

• Fat-soluble vitamins (A, D, E, K) — absorption multiplies with fat
• Iron — up to 2x better on an empty stomach; vitamin C increases absorption
• Calcium carbonate — better with food (needs stomach acid)
• Calcium citrate — doesn't depend on food

3. Interactions

Some nutrients help each other's absorption, others hinder it.

Positive interactions:

• Vitamin C + iron = better absorption
• Vitamin D + calcium = better absorption
• Black pepper (piperine) + curcumin = significantly better absorption

Negative interactions:

• Calcium + iron = worse absorption
• Coffee/tea + iron = tannins block it
• Zinc + copper = compete

4. Gut Health

A healthy gut absorbs nutrients better. If you have digestive issues, absorption may be lower.

• Stomach acid levels — low acid (e.g., from PPI medications) reduces mineral absorption
• Gut microbiome — a healthy microbiome supports nutrient absorption
• Inflammation — chronic gut inflammation reduces absorption

Practical Tips to Improve Absorption

1. Choose a well-absorbed form — magnesium glycinate vs oxide, iron bisglycinate vs sulfate
2. Time it right — fat-soluble with food, iron on empty stomach
3. Use positive interactions — vitamin C alongside iron, vitamin D with calcium
4. Avoid negative interactions — separate calcium and iron by at least 2 hours
5. Split your doses — the body absorbs a limited amount at a time (especially calcium — max 500 mg at once)
6. Take care of your gut — probiotics and fibre-rich food support absorption

Is Cheaper Always Worse?

Not necessarily. Price depends on many factors — brand, packaging, marketing. What matters:

• Active ingredient form — this affects absorption the most
• Elemental amount — not the capsule's total weight
• Price per serving — not the package price

A cheap magnesium citrate may be a better choice than an expensive magnesium oxide, because the form affects absorption more than the price.

Common Mistakes

1. Choosing based on price alone — the cheapest product in the worst form is a waste of money
2. Taking the entire daily dose at once — the body absorbs a limited amount at a time
3. Ignoring interactions — iron with coffee, calcium with iron
4. Ignoring the form — "magnesium is magnesium" is not true
5. Ignoring gut health — even the best supplement won't help if absorption is impaired

Frequently Asked Questions

Are chelated minerals always better? Chelated forms (e.g., bisglycinate) are typically better absorbed and gentler on the stomach, but also more expensive. Citrate forms are a good compromise.

Are salt forms bad? Not necessarily — some are cheaper and work well enough. Magnesium citrate is a salt form but absorbs well.

How much does food affect absorption? Significantly. Fat-soluble vitamins without fat absorb up to 50% worse. Iron without vitamin C also absorbs worse.

Are liposomal forms better? Liposomal forms (e.g., liposomal vitamin C) may offer better absorption, but are significantly more expensive. An adequate dose of the standard form is usually effective.

Does an empty stomach affect all supplements? No. Some (iron, amino acids) absorb better on an empty stomach, others (zinc, fat-soluble vitamins) need food.

References

1. Rein, M.J., Renouf, M., Cruz-Hernandez, C., Actis-Goretta, L., Thakkar, S.K. & da Silva Pinto, M. (2013). Bioavailability of bioactive food compounds: a challenging journey to bioefficacy. British Journal of Clinical Pharmacology, 75(3), 588–602.
2. Hurrell, R. & Egli, I. (2010). Iron bioavailability and dietary reference values. American Journal of Clinical Nutrition, 91(5), 1461S–1467S.
3. Pressman, P., Clemens, R.A. & Hayes, A.W. (2017). Bioavailability of micronutrients obtained from supplements and food. Toxicology Research and Application, 1, 1–2.

See also:

• Chelated vs Regular Minerals
• Supplement Forms and Bioavailability
• Magnesium Types Compared

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Disclaimer

A food supplement is not a substitute for a varied and balanced diet and a healthy lifestyle.