Bioavailability

What is bioavailability?

Bioavailability is a term used in medicine, pharmacology and nutrition to describe how much and how quickly an active ingredient or nutrient is actually available after being absorbed by the body – i.e. into the bloodstream, where it can take effect. In other words: It is about what proportion of a substance is available in the body unchanged after ingestion.

In a medical context, bioavailability usually refers to drugs and active ingredients. In nutrition, it describes how well a nutrient is released from food, absorbed and utilised.

Why is bioavailability so important?

Bioavailability directly influences the effectiveness of a drug or the supply of nutrients to the body. No matter how healthy or effective a substance may be, if it is not absorbed sufficiently, it cannot be effective. That is why bioavailability is a key factor in the development of drugs and in the evaluation of nutrients in food or food supplements.

Example: Vitamin C Liquid preparations are often absorbed more quickly and better than tablets. Likewise, Beta-Carotin from dietary supplements a higher bioavailability than from plant-based foods.

How is bioavailability measured?

Bioavailability is determined by measuring the concentration of an active ingredient or nutrient in the blood or other body fluids after ingestion. The proportion that reaches the systemic circulation unchanged is calculated. Bioavailability is often expressed as a percentage.

When an active substance is administered intravenously, its bioavailability is by definition 100% (absolute bioavailability). When taken orally, it is usually lower because the substance is first released in the digestive tract, absorbed and partially metabolised in the liver (first-pass effect).

Factors influencing bioavailability

• Physical and chemical properties of the active ingredient or nutrient (e.g. solubility, stability)
• Formulation and dosage form: Tablets, capsules, liquids, nanoparticles, liposomes, etc.
• Lebensmittelmatrix: The structure and composition of food influences how well a nutrient is released.
• Begleitstoffe: Fat promotes the absorption of fat-soluble vitamins and carotenoids; fibre or fat substitutes can inhibit absorption.
• State of health: Gastrointestinal function, enzyme activity, bile flow and other individual factors play a role.
• First-Pass-Effekt: Metabolisation in the liver before reaching the systemic circulation reduces bioavailability.
• Interactions with other foods or medications: Some substances may promote or inhibit absorption.

Bioavailability in nutrition

Bioavailability is also crucial for nutrients. For example:

• Beta-carotene: Fat-soluble, better absorbed when consumed with fat. Cooking and chopping increase bioavailability, while raw foods and fibre-rich foods can reduce it.
• Vitamins: Water-soluble vitamins (e.g. vitamin C) are absorbed differently than fat-soluble vitamins (A, D, E, K).
• Minerals: Iron from animal sources is better absorbed than iron from plant sources. Vitamin C can improve iron absorption.

Improvement of bioavailability

• Combination with fats (e.g. oil with vegetables)
• Chopping, puréeing or cooking food
• Use of special formulations in medicines (e.g. nanoparticles, liposomal capsules)
• Avoidance of inhibiting factors such as excessive fibre consumption or certain medications

Summary

Bioavailability describes how much of an active ingredient or nutrient actually reaches the body after ingestion and becomes effective. It is a key factor in the effectiveness of medicines and the supply of nutrients. Many factors influence bioavailability, including the chemical properties of the substance, its formulation, the food matrix and individual health aspects. Understanding bioavailability helps to optimise the effectiveness of medicines and improve healthy nutrition.