Expert Nutrition

Bioavailability of Nutritional Supplements

Bioavailability is defined as the degree and rate at which a substance (as a drug or supplement) is absorbed into a living system or is made available at the site of physiological activity. On this page we will discuss factors that can affect the bioavailability of nutritional supplements and help to bust some common myths along the way.

To start with it is important to understand that all vitamins and minerals have different absorption rates and there are many factors that can affect the absorption of these vitamins and minerals into the body. Some of these factors are a function of the person taking the nutrient and are dependent on the age of the person, the integrity of their digestive system, the state of their health, the time of day, the person's gender, and if the supplements was taken on a full or empty stomach. Additionally people whose nutrient needs are greater, such as growing children, pregnant or lactating women, and those who are currently deficient, may have significantly enhanced absorption rates for certain nutrients.

Recently, some individuals and companies have made claims that their products are superior because they are "98-percent absorbed". This is a misleading statement because there are too many variables to imply that an individual's absorption is a certain percent of the material consumed. Even absorption of minerals from food sources can vary significantly. Boron, molybdenum, and iodine can be absorbed at over 90 percent while the average absorption rates of zinc, copper, and selenium can range from 30 to 80 percent depending on the form. It should seem reasonable then, that stating an average absorption rate is very misleading.

One way to evaluate supplements to see if they have good bioavailability is to look for products that have been independently tested and certified. For example some products meet British Pharmacopoeia (BP) standards for disintegration meaning that they are fully disintegrated and made available to the body within 30 minutes of consumption. BP standards can also be used to evaluate potency and uniformity. These products can normally be identified by reading the nutritional information panel as there will be a statement (normally in bold or highlighted) that says they have tested and evaluated to meet certain standards.

We know that there are many factors that affect the bioavailability of vitamins and minerals and although we have no control over many of those factors listed above there are a few things that help to distinguish some quality nutritional supplements. Two important factors that spring to mind are the form in which the supplement comes in (ie liquid vs tablet) and the form of which the active ingredients come in (chelated minerals vs mineral salts). For more information on these subheadings, please follow the links below.

1. Bioavailability cited on the 1st Feb 2007.
2. National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. Department of Health and Ageing, Canberra 2006.

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