Bioavailability is a term heard often when discussing medication. Do consumers know what it means??
For a medication to be useful for the patient, it needs to be bioavailable for the body to use. In another way, when you take a tablet the medicine in that tablet needs to be able to get out of the digestive system and into the blood stream. There are two factors that affect bioavailability:
• Solubility of the drug in digestive fluids
• Permeability of the drug. How easily does the drug pass through the digestive lining into the blood stream.
A drug that is very soluble in the digestive system usually has a high bioavailability. A drug that is highly permeable has a high bioavailability. There is a classification system that describes bioavailability pictorially. The picture below describes the BCS (Biopharmaceutics Classification System). Each drug molecule can be classified as Class I, II, III or IV. Class I drugs are usually very easy to formulate into a medication. Many of the drugs in development today are Class II or IV. These drugs are very difficult to formulate because they are very insoluble or do not permeate digestive lining. In the pharmaceutical formulation business, those compounds are nicknamed “brick-dust”, something that isn’t going anywhere.
For more information, please see the following.
Bioavailabilty of nutritional supplements is also studied. There are a vast number of metal based nutrients that a person needs in trace quantities to survive. Did you know that your body contains 3.5 grams of iron and 2.5 grams of zinc? Here is a short list of some of the important trace metals and their role.
• Iron — blood function
• Copper — electron and oxygen transport
• Zinc — antioxidant and immune system properties (proposed!)
Food Fortification versus Nutritional Supplementation
Food is fortified with trace elements so deficiencies in the population are reduced. Cereal is fortified. Read the Nutrition Facts on the closest box of cereal. In addition to added vitamins you’ll see “zinc (zinc oxide)”. Zinc oxide is very inexpensive and very stable; a good candidate for food fortification. It does, however, have fairly poor bioavailability. Luckily, you don’t need a lot of zinc daily. The USRDA for zinc is 8 mg to 11 mg.
Nutritional supplements are designed to compensate for low bioavailability by utilizing a metal containing organic chemical for better bioavailability. An example is zinc picolinate. Zinc picolinate is considerably more bioavailable than zinc oxide; it is also more expensive hence its use in nutritional supplements. (Barrie, SA, Wright, JV, Pizzorno, E, Kutter, and Barron, E Comparative absorption of Zinc Picolinate, Zinc Citrate and Zinc Gluconate in Humans. Agents and Actions. 21 1/2 (1987)
Please, if you are considering taking a nutritional supplement in addition to your normal daily diet TALK WITH YOUR DOCTOR. Excessive intake of most anything can be very bad. Too much zinc, for example, “Zinc toxicity can occur in both acute and chronic forms. Acute adverse effects of high zinc intake include nausea, vomiting, loss of appetite, abdominal cramps, diarrhea, and headaches.”
For more information on Zinc supplementation: The Office of Dietary Supplements, National Institute of Health.
© Grove Ridge Consulting, 2011