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Bioavailability Of Nutritional Supplements

Not every nutrient you swallow is absorbed by your body! The bioavailability of nutritional supplements is an often overlooked factor when comparing supplement brands. It has major implications for the efficacy and particularly value for money of a supplement.

So when it comes to all those costly ingredients you’re paying for, bioavailability basically means “the proportion of a nutrient or bioactive ingredient that was absorbed from the gastrointestinal tract” (1) for use or storage in the body.

After passing through the intestinal wall lining, the ingredients enter your bloodstream and find their way to their target organ or body system where they go to work performing their specific duties to support your health and make you feel great – well that’s the plan anyway.

Under the US Dietary and Health Education Act 1994 (DSHEA) nutritional supplements are regulated under ‘food’ GMP – this means absorption rates do not have to be tested – this has played a part in creating a credibility problem for the supplement industry.

Research data on bioavailability levels for supplements is very limited and incomplete to say the least. There is an urgent and continuing need to develop simple in-vitro methodologies to determine bioavailability of nutritional supplements.

Standardized measurements (of bioavailability) are what we need but for numerous reasons (cost being the major one) it looks like it will be many years before this eventuates.

So, one very important thing that you need to keep in mind is -

…the ingredients and amounts of each on a supplement label are in no way an indication of how much actually makes it into your bloodstream for use in your body!

Different factors such as;
disintegration time

dissolution percentage

types of excipients used

nutrient forms

presence of co-factors or inhibitors in the formula

interactions with drugs

time of the day taken

area in the body that disintegration occurs (supplement delivery system)

level of absorption at the intestine and cellular level

your body’s nutritional needs

all influence the total level of bioavailability.

The label gives you no idea how bioavailable each ingredient is!
There are also nutritional and physiological factors involving not the product but rather the individual taking the supplement. Being pregnant is one example, being elderly or sick are others. These are highly individual so I will limit this article to factors related to the supplement only.

High quality supplements are formulated to allow much higher levels of bioavailability than cheaper, mass produced vitamin and mineral products. This is because they are science based and use more sophisticated manufacturing processes. This is one reason why they cost more (but work better!).

OK, let’s get down to the nuts and bolts of bioavailability and how it can be increased.

I’ll explain how you can use ‘bioavailability in nutritional supplements’ as criteria to evaluate and compare supplement brands – this involves requesting some ‘missing’ information from supplement companies.

Questions to ask are listed for you below.


Disintegration refers to a tablet’s ability to break apart and fragment into small particles in order to distribute the contents - a rather important thing that we take for granted will happen. Let’s discuss that further down.

Even though disintegration has occurred that doesn’t mean that the ingredients have dissolved! A tablet can have fast disintegration time yet be biologically unavailable i.e. the ingredients can’t get in to do their magic.

Dissolution refers to the ability of a supplement to dissolve in solution – expressed as a percentage. Supplements which dissolve most rapidly have the highest bioavailability because nutrients have a limited and defined region of absorption in the intestinal tract [Bland, 1985] (2)

Non-governmental, not for profit organizations such as the United States Pharmacopeia (USP) and British Pharmacopeia (BP) have set standards assuring integrity and uniform quality of: drugs, excipients, dietary supplements, vitamins, and minerals.

These standards include disintegration and dissolution rate guidelines for supplements (USP section <2040>) and pharmaceutical drugs.

When supplements meet these standards you can have confidence that their formulation process is representative of the best state-of-the-art technology currently available.

The USP works closely with the FDA and pharmaceutical industry in producing these quality standards (which have been produced since 1820). Today they are recognized worldwide and are enforced not only by the FDA but by the governments of many countries.

Examples of USP disintegration standards for tablets;

calcium supplements must dissolve in 30 minutes

magnesium supplements must dissolve in 45 minutes

multi vitamin/mineral formulations in 45 minutes

Professional standard supplements disintegrate within 20-30 minutes!

If you would like to see the British Pharmacopeia disintegration test for pharmaceutical grade tablets please follow this link. Unfortunately these disintegration standards are only guidelines when it comes to supplements. In other words they’re voluntary.

Reputable supplement companies however always manufacture in line with USP/BP standards. It’s important to always check on this when evaluating and comparing supplements!

It’s well known that some cheap, mass produced supplement formulations do not break down and pass straight through the body intact! If this happens (with your supplement) your money goes straight down the toilet.

Perhaps you’ve heard the documented stories of nurses finding intact supplements in patient’s bedpans! 

At the bottom of the ‘Supplement Facts’ label on a supplement bottle is a listing called “Other Ingredients”. These are inactive substances added into the formula to give the desired consistency, form and assist the manufacturing process. Collectively they are referred to as ‘excipients’ and the number and type used can affect a tablets ability to disintegrate.

To learn more about whats an acceptable tablet binder including which ones should and shouldn’t be in your supplement please follow this link.

There are 4 effective ways in which nutrients can get into your blood stream.

Via Injection

Via the mucous membranes of the mouth.

Via the lining of the walls of the upper intestine.

via the lining of the walls of the colon (suppositories)

Nutrients in supplements enter the blood stream via the small intestine. That’s the way nature designed it to happen. Just like when we eat food - the nutrients are eventually delivered to the intestine for absorption.

The actual delivery of the nutrients from the stomach to the intestine is a major factor to be considered because stomach acid and some enzymes in the stomach significantly damage or destroy certain nutrients!

Vitamins and minerals are not affected by stomach acid but others including pancreatic enzymes, some vegetable enzymes and expensive/highly beneficial ingredients like L-Glutathione, alpha lipoic acid, SAMe and herbals are.

At the end of this article you’ll find a table listing examples of common supplement ingredients which are susceptible to stomach acid.

So if a special delivery system to overcome this problem is not employed then bioavailability is significantly reduced! - as is your supplements’ effectiveness and value for money (not to mention your health!).

NOTE: Some experts believe that due to damage from stomach acid only 10-15% of the active ingredients actually get into the blood stream. Other experts would of course disagree. More research is needed!

What is this special delivery system?
Enteric Coating
Enteric coating has been extensively used for many years with pharmaceutical drugs (which is one reason why drugs work so well and so quickly). Enteric coating provides a protective layer on a tablet as it passes through the stomach. Once the tablet reaches the duodenum (small intestine) the coating reacts to the alkaline environment, strips away and the tablet contents are harmlessly released.

A much greater level of bioavailability is thus guaranteed.

Enteric coated nutritional vitamin supplements do not have to be taken with meals – as is the case with non-enteric coated tablets.

Why is enteric coating rarely used with nutritional supplements?
Cost and knowledge!

It’s a very expensive technology and since most supplements are made to a price they can’t afford to use it. On top of that many supplement companies are merely marketers – not science based companies – so they don’t have the technical know how.

It doesn’t matter whether a supplement is in a liquid, tablet or capsule form - if it is released in the stomach then its contents will be affected.

Manufacturers of liquid products who claim ridiculously high levels of bioavailability always conveniently forget to mention this!

How do leading companies explain the fact that they don’t use enteric coating?
Three of the industry's four best vitamin supplements which are reviewed and compared in this site, do not employ enteric coating! So I asked their suppliers/manufacturers “why?” They all said they don’t need it because nature ensures nutrients reach the intestine for absorption.

That’s true, to varying degrees, but as supplement consumers what we are interested in is how much of each of the various nutrients reach the intestine? That’s the real issue because we’re paying for those nutrients! Basically they sidestepped the question.

If a supplement doesn’t contain ingredients susceptible to stomach acid then enteric coating is not needed. This is of course the answer as to why many supplement companies don’t need to use enteric coating.

The problem with this is that most of the ingredients affected are important and expensive/efficious ones that you definitely want in a quality supplement aimed at complete good health.

So the decision on whether to use enteric coating as a delivery system rests on the type of ingredients, integrity and structure of the company, and objective of the product.

The product which does use enteric coating is called Total Balance from the Xtend- Life Company, based in New Zealand.

This is the supplement my family and I take, and the bioavailability/enteric coating issue was a major factor in our decision to originally use it.

Mr. Warren Matthews, the chairman of Xtend-Life offered the following example as to the importance of enteric coating: (quoted with permission)

“For many ingredients in a supplement it does indeed make a big difference as to where they are released in the body. Let me give you a fairly detailed example using L-Glutathione which is extremely important for the health of your cells. This substance will be severely damaged if released in the stomach. This is well documented! It must be released in the upper intestine in order to be effective.

The amount of L-Glutathione we consume in food is very low and has little or no impact on the levels within our blood. This is because the L-Glutathione which is present in food is damaged by stomach acid. Because of this the body relies on the liver to synthesize L-Glutathione.

Whereas relying on the liver to produce this nutrient and others is fine when you are young and healthy, but it is a different story as you get older. Your organs are not as efficient and as a result the production of many essential nutrients is reduced, so it is easy to slowly develop deficiencies in many essential ingredients.

You will not even be aware of these developing deficiencies unless you have extensive blood testing. I am sure that you appreciate how critical it is that you don’t develop nutrient deficiencies, as they are the primary cause of most diseases.

If you want to do everything to help yourself avoid diseases then you must ‘top up’ with these key nutrients and this is simply not possible using a conventional tablet or capsule. The nutrients need to bypass the stomach, and the only practical way to do this is with an enteric coated tablet which we use for Total Balance and our Neuro-Natural range. An alternative would be by intravenous drip, or suppositories, neither of which is practical for most people.

In summary on this point, those people who suggest that there is no point in enteric coating tablets unfortunately do not either understand bio-chemistry or are unaware of the importance of certain ingredients.”

If you would like to learn more about the delivery system for enteric coating and vitamin absorption please follow this link.




Nutrients can exist in more than one chemical form!

Different forms result in different levels of bioavailability.

For example zinc and copper have average absorption ranges of 30% – 80% depending on the source and the individual user. That’s a huge difference!

So disintegration and dissolution levels by themselves are insufficient indicators of bioavailability in nutritional supplements.

The nutrient 'form' must be considered!
Using current research we can determine the more bioavailable forms of some nutrients and then check to see if that form is included in a supplement we are evaluating.

Minerals are probably the most well known and well researched example when discussing bioavailable forms.

Minerals are so crucial to optimal health and vitality yet many people do not take in enough minerals from diet alone. They are very hard to absorb. The body often mis-regulates their transport and some, sharing the same metabolic pathways, will compete against one another resulting in too much of one and a deficiency of another.

Some minerals can be manufactured in certain forms that are better at ‘getting in’.One such form is the chelated form.

A ‘chelator’ is a substance formed of molecules that tightly bind to metal atoms (minerals in this case) and forces them to go wherever the chelator goes - helper molecules which assist minerals on their journey into our bodies.

This bound pair is a compound and it is called a chelate. In the simplest sense you could think of the term ‘chelated’ to mean ‘firmly attached’.

So, chelates enhance the passage of minerals through the intestinal wall lining into the blood, tissues and cells thus increasing total mineral bioavailability. They allow for greater amounts of minerals to enter your blood stream than what your body would ordinarily allow.

There are different types of mineral chelates
The most absorbable form of mineral chelates is called Organic acid salts. There is a great deal of accepted research available to support this.

Examples of these chelates which you want in your supplement are: Picolinates Gluconates Lactates Luccinates Citrates Orotates Nicotinates
Carbonates (usually classified as inorganic but function more like organic)
For example:

If calcium is included in a supplement as an organic salt you will see it listed on the nutritional facts label as;
Calcium as Calcium Citrate
Start checking your labels!

What you don’t want to see are inexpensive and relatively non-absorbent inorganic mineral salts:
Chloride Hydroxide Oxides Phosphates Sulfates

Organic salt chelators do not however form a particularly strong bond with minerals atoms and the bond can be broken by water molecules in your body or random cell jostling. If this happens the mineral does not get its forced ride into your blood stream and cells.

Another form of chelate which produces a stronger bond with Amino Acid Chelate. The minerals are chelated with amino acids. (You guessed that – right!) The body readily absorbs amino acids.

On a Supplement Facts label you’ll commonly see amino acid chelates listed like this example:
'Boron as amino acid chelate'
But this type of listing is not good enough!

Products labeled like this may not be true chelates – it depends on the source and properties of the chelating agent. If a supplement contains true amino acid chelates the name of the amino acid to which the mineral is chelated must be shown.

Keep checking those labels!

Not all amino acid chelates are superior to other forms. For example Magnesium and Calcium have been shown to offer about the same bioavailability in the organic salt chelate form as in the amino acid chelated form.

* That’s why leading professional level supplements differ in their usage of chelated mineral forms.

A quick mention about Colloidal Minerals
There are a number of supplements available that promote the use of ‘colloidal minerals’. Manufacturers of these products commonly claim that colloidal minerals have 98% absorption.

The bottom line is that this has never been proven!

There are no documented clinical tests what-so-ever to show that colloidal minerals are absorbed at all.

Without clinical research to support the use of a particular ingredient/ingredient form it shouldn’t be included in a supplement.

Other chelates exist (e.g. Kreb’s cycle intermediates) but we don’t need to dig down any deeper - its gets too technical. The main ones have been discussed above.

There are other important factors which also effect absorption such as ‘co-factors’ (nutrients which help other nutrients do their job) and the synergy of the formula. You can read about these in my ‘synergy’ page.

Nutrients not absorbed can still be beneficial !

Don’t worry about the common belief that excessive nutrients produce expensive urine and are of no benefit to you.

Research has shown that many nutrients have important roles to play by remaining in the lumen of the intestine rather than being absorbed. For example vitamin C and calcium in the large intestine offer protection against cancer by inhibiting the conversion of agents into carcinogens and to enhancing healthy flora.

Bioavailability of Nutritional Supplements - Lets Sum it all up! 

High quality multi nutrient supplements have been formulated by highly qualified scientists to offer much higher degrees of bioavailability. This is not the case with cheap or middle of the road products.

So please don’t let price be your determining factor when selecting supplements.

If you are spending good money on what you think is a quality supplement it’s crucial to know that a high percentage of the ingredients will actually make it into your bloodstream.

There is a lot of conflicting and inconclusive science as to the most bioavailable form for many nutrients. Therefore it becomes impossible in trying to determine the absolute most bioavailable form for every common ingredient used in supplements. Use the established facts above to guide you in this regard.

For some nutrients however the supporting science is strong. Take Resveratrol as an example - an expensive, beneficial phyto-chemical found in most quality multi nutrient supplements. There is clear evidence that Resveratrol in the ‘Trans’ form is significantly more bioavailable than in the cheaper ‘Cis’ form.

In cases like this it is easy for you to check and compare. But finding credible research is a real challenge for consumers.