What does the term bioavailability mean?

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Bioavailability has been broadly defined as the “absorption and utilisation of a nutrient”.1 This means that it is all very well taking a drug or a nutrient, but what really matters is how well we can absorb the substance and then how well can our body make good use of it.  So people prescribed drugs such as calcium channel blockers and some statins such as simvastatin and lovastatin are advised against drinking grapefruit juice since the anti-oxidants in the grapefruit juice interact with the drugs and make them more effective by increasing their bioavailability, leading to the danger of an overdose because the substances in the drugs are uptaken more effectively by the body.  Or, for the opposite effect, people taking Orlistat, a drug designed to prevent the absorption of fat may well suffer from Vitamins A, D, E and K deficiencies since these vitamins are fat based nutrients, so Orlistat drastically reduces the bioavailability of all 4.

A different example of bioavailability is demonstrated by the uptake of the vitamin C found in oranges and blueberries. In 100gm of orange there is 59.1 mg of Vitamin C where as blueberries have a paltry 9.7mg of vitamin C.2 However, oranges contain 0.9mg of antioxidants,3 whereas blueberries contain about 53mg per 100gm fresh, ripe fruit.4  This difference means the vitamin C in blueberries becomes much more bioavailable and, for this reason, blueberries are a much better source of vitamin C than oranges.  This better uptake is due to synergy: the interaction of 2 substances that, combined together, make something greater than the 2 parts taken separately.

It is synergy that Dr Janeel Henderson is referring to in the above video clip.  She is saying that a cheap multi not only has inferior constituents but these constituents are also not in balanced amounts to get proper synergy, so do not have good bioavailability. At best, a cheap multi is a waste of money; at worst it is actually bad for us.

Another example where we need a supplement to have good bioavailability for it to work is when we supplement with minerals.  Without a shadow of doubt, the best form of nutrition comes from our food; the nutrients exist in proper synergy.  Modern, highly processed foods apart, our body knows what to do with proper food.  In an ideal digestive situation, when we eat real food, we break the food down into its component nutrients which the liver processes and repackages as it needs to.  Sadly modern farming methods, which use agro chemicals and not natural fertilisers, mean that our soil has been leached of many important nutrients so it really is necessary to take supplements to stay healthy and active into old age – either that or we end up taking drugs instead – to lower the blood pressure, to reduce the cholesterol, to lower the inflammation and pain, to help the pancreas deal with the sugar load, to keep our brain working a bit longer- the list is endless and the drug companies happy.  Most minerals we eat the body likes to get from animal or fish protein: in the digestive process, it breaks down the protein, cleaves the mineral, be it magnesium, zinc or calcium, for example, from the protein, shuttles it to the liver where further action is taken with the goodies.  So for a mineral supplement to become bioavailable, it should be attached to a protein, a process called chelation.  If the mineral is attached to a much cheaper vegetable source, the industry calls this a salt, in order to get enough of the mineral to do any good we usually unpleasant side effects such as the trots.  So a quick example is magnesium;  magnesium glycinate is magnesium chelated to glycine, a protein.  Magnesium citrate is magnesium attached to citric acid.  Magnesium citrate or oxide or any other salt compound is much cheaper but much less bioavailable than magnesium glycinate etc.

There are other ways of making a supplement or drug more bioavailable. Taking them in liquid form is more easily absorbed in the body, with the obvious problem of unpleasant tastes making this not always possible.

Finally, in the above paragraph but one, I referred to an ideal digestion.  This is very rare these days, due to stress, which weakens the gut walls, making them porous; the overeating of difficult to digest foods like wheat and dairy, which causes great damage to the gut walls; drinking chlorinated tap water, which slowly decimates the good gut bacteria; taking anti-biotics without restoring the good bacteria afterwards plus excessive sugar eating, all 3 of which lead to a proliferation of bad bacteria in the guts.  Both drug companies and the high quality supplement companies know the state of the average gut and so there is a lot of research going into using skin creams to make the drug or supplement bioavailable.  What we rub on our skin we do absorb and this by-passes the dysfunctional digestive tract.

So, to quote Charles Poliquin, “It isn’t so much what we eat that matters, it is what we assimilate.”


  1. Anekonda T S.  Resveratrol – a boon for treating Alzheimer’s disease:  Brain Research Review 52 (2006) 316-326 []
  2. USDA nutrient data base []
  3. Carlsen MH.  The total antioxidant content of more htan 3,100 foods, beverages, spices, herbs and supplements used world wide.  Nutrition Journal 2010,9:3 []
  4. Ribera A E et al.  Maturity stages in high bush blueberry grown in Southern Chile.  J Soil Sc Plant Nutr 10(4):509-536 (2010 []

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