The Bioavailability Spectrum 

Let's take a closer look at the bioavailability of supplements on a spectrum, from least bioavailable to most bioavailable. On the low end of the spectrum you would have an inexpensive, store bought, hard-packed tablet. Something brightly colored that you can't break with your fingers. Such supplements have many fillers and binders, including ingredients that can be found in wood putty and tar. You can't take these on an empty stomach, or else you'll get an upset stomach. These are difficult to digest and breakdown, and often times your body doesn't at all. And these have been known to have been passed whole! For that reason you can understand why they have a bioavailability of 0-25%. So, just as a reminder, when you look at the daily values of nutrients on the label of these products, your body is not getting those percentages of nutrition, but rather up to 25% tops.

Moving up the bioavailability spectrum we come to the capsule delivery system. They have no fillers or binders, and you usually have to take larger quantities of these because they are not very concentrated. The bioavailability is a little better, but still only 40-60%.

Getting higher up the bioavailability spectrum brings us to liquid supplements. These are better then the previous two in bioavailability and range between 80-90%, but many liquid herbs and oils do not taste very good.

Finally we arrive to isotonic-capable supplements. Isotonic supplements are the most bioavailable delivery of supplements and are up to 95% absorbable.

Isotonic-Capable Supplements 

Isotonic nutritional formulas are an osmotic adjuvant system composed of a series of related formulas. All of the formulas may be used to manufacture products for use in human nutrition that, when prepared for ingestion as solutions are of the same osmotic pressure (or osmolarity) as most of the fluids in the human body. By definition, these solutions may be called isotonic “equal tonicity.”

Specifically, the fluid pressures of the solutions across semi-permeable membranes (the walls of the small intestines, for example, are semi-permeable membranes) in biological systems are generally referred to as having a particular osmolarity. For the purposes of this discussion, the osmolarity is measured in units referred to as milliosmoles/kilogram (mOs/kg). It can be said that when solutions on opposite sides of a membrane have the same osmolarity, they are iso-osmotic or isotonic, regardless of whether that osmolarity is 100 mOs/kg or 650 mOs/kg.

However, in human medicine that definition is considerably narrowed. Normal human blood serum (the fluid portion of the blood without cells and platelets) has an osmolarity of 288.6 mOs/kg, as do most other fluids in the body (notable exceptions being sweat and urine). Therefore, in human medicine when a solution’s osmolarity is the same, or nearly the same as that of normal human blood serum, it is referred to as isotonic.

Black’s Medical Dictionary defines isotonic as follows: “ISOTONIC is a term applied to solutions that have the same power of diffusion as one another. An isotonic solution in medicine is one that can be mixed with body fluids without causing any disturbance. Solutions that are weaker or stronger than the fluids with which they are intended to be mixed are known as hypotonic or hypertonic respectively.”

In 1905, P. Carnot and A. Chassevant, French physiologists, reported that isotonic saline (0.9% sodium chloride) solutions administered orally to dogs emptied from the stomach more rapidly than either a hypotonic solution (water) or a hypertonic solution (3% sodium chloride).

Over the following 91 years, this physiologic phenomenon has been repeatedly verified in many species of animals and in humans. Researchers at the University of Leeds, Guy’s Hospital in London, Baylor University, and the Mayo Clinic, among others, have shown that not only do isotonic solutions leave the stomach faster, but also that the osmolarity of the stomach contents (its osmotic pressure) is one of the controlling mechanisms for the rate at which the stomach empties.

Micronutrients (vitamins and minerals) are most commonly consumed in solid (tablet or capsule) form. These solid forms must be broken down in the stomach and the active ingredients (micronutrients) must then dissolve in the gastric fluids in the stomach. This disintegration and dissolution process is often slower than any other process involved in the absorption of a micronutrient or a drug. When the active ingredients have dissolved, the body must adjust the concentration of the stomach contents to become an isotonic solution before the contents can proceed into the small intestine for absorption. If there are any foods or beverages in the stomach at the time the tablet or capsule is taken, the active ingredients will be delayed further in their transit to the small intestine until the food is properly prepared to leave the stomach.

Absorption into the bloodstream is a function of surface area, and the small intestine has a huge surface due to its length, its many folds, and the microvilli (minute finger-like projections) on intestinal epithelial cells. In comparison, the surface area of the stomach is very small, and the absorption that occurs there is negligible. The fastest and greatest absorption takes place in the small intestine.

It is important to note that not all liquids are isotonic capable, again it is a specific ratio of medicine or nutrients to water which makes it isotonic. Everything that you ingest and put into your stomach has to be digested down to an isotonic state before it is released to the small intestine. When you eat some food and take a standard pill or capsule vitamin, it all remains in your stomach digesting for anywhere from 40 minutes to 4 hours. At that point a certain amount of dilution of nutrients has taken place. Some low quality pills do not even break down due to harsh fillers and binders, but still pass to the small intestine where none of the content of the supplement can be absorbed. This is why the bioavailability of pills and capsules are so significantly lower than isotonic capable supplements.