here's some good info regarding bioavailability of nutrients from my enewsletter from Infinity2, sorry about any product refs..

"Thousands of people take supplements everyday, but few people know what is actually in the supplement they're taking. In order to know what's in the supplement, you must first know how to read and interpret the information presented on the label. Unfortunately, when it comes to evaluating nutritional products by their labels, the old adage, "You can't believe everything you read," seems to hold particularly true. It is hard to sort out fact from fiction when it comes to some of the inflated claims made on product labels. It is even more difficult to understand how to compare one product to another based on listed ingredient amounts.

Take enzymes for example. Some companies indicate enzyme potency in milligrams. While this may look impressive on the label, it is actually meaningless. Enzyme effectiveness depends on activity, not on weight. Other companies choose to express enzyme activity in an obscure system of units that originated in a foreign country. Some enzyme products keep you completely in the dark and don't list the potencies at all.

The system for determining enzyme potency used by the American food industry is derived from the Food Chemical Codex (FCC) and is accepted as the standard by the FDA. The activity of enzymes such as protease, lipase, amylase, etc. can be expressed in units which are well-defined by the FCC (in English). Anyone who cares to do so may look up the protocol for assay in the FCC reference book. If all enzyme activity were expressed in FCC units, comparisons could easily be made.

Trying to compare the labels on vitamin and mineral supplements can also create confusion. Vitamin companies may use their labels to inflate their allegations or hide their product's flaws. Some supplements appear to be powerful combinations of vitamins, but in reality have little nutritional value and may even create drug-like reactions in the body. Weighing the effectiveness of vitamins, then, comes down to understanding some fundamental differences.

In an attempt to standardize supplement labels and reduce confusion, new government regulations have been put in place. A key part of the new supplement labels is the Supplement Facts section where specific nutrients are listed by amounts and as a percentage of the Daily Value (%DV). But what is the Daily Value and how is it calculated?

The Daily Values are standard values developed by the Food and Drug Administration (FDA) for use on food and supplement labels. The Daily Values were created based on two sets of reference values, the DRI and the DRV. The DRI (Dietary Reference Intakes) are the food label values for protein, vitamins, and minerals based on population-adjusted means of the RDA (Recommended Dietary Allowances). The DRV (Daily Reference Values) are food label values for nutrients and food components (such as fat and fiber) that do not have an RDA value but do have important relationships with health. Together, the DRI and DRV make up the Daily Values used on food and supplement labels.

The RDAs used to calculate the DRIs and the DVs (Daily Values) were originally designed in the 1940's for the purpose of providing war rations that would provide adequate nutrition to keep military personnel from becoming deficient in these nutrients. These values were generally determined using laboratory experiments (and military experiments) to ascertain the amount of a synthetically created nutrient that is required to prevent or correct a nutrient deficiency. These values were then adjusted according to how well the nutrient used in the experiment was absorbed and then adjusted again based on the mean (or average) of the population's needs. For example, the iron (Fe) requirement for adult males is calculated as follows:

Males lose 1.0 mg of iron each day that must be replaced or iron deficiency anemia will occur. The type of iron used as a baseline has a 10% absorption rate. Therefore the RDA was set at 10 mg per day for men. For adolescent males the RDA is 12 mg/day, for premenopausal women 15 mg, and for pregnant women 30 mg. The Daily Value is then calculated based on the average of the requirements for the various subgroups of the population, which for iron is 12 mg/day.

Iron found in a supplement or food will be listed on the label as a percentage of the Daily Value of 12 mg/day. If a supplement contains 6 mg of iron it will be listed as 50% DV regardless of whether that form of iron has a 10% absorption rate or a 100% absorption rate.

As you can see, the labels do not tell you much about the "biological" daily value of the nutrient you are ingesting. The labels do not take into consideration that the absorption of the nutrient in that particular supplement may be higher (or lower) than the form of the nutrient used to calculate the daily value. For example, ferrous sulfate is the most commonly used form of iron in supplements, but is very poorly absorbed (10% absorption). In contrast, the amino acid chelated form of iron, Ferrochel(tm) has a 70 to 75% absorption rate, which is much higher than ferrous sulfate. This means that a supplement containing 5 mg of iron as Ferrochel(tm) will actually supply 3.5 to 3.75 mg of iron to the body. This is three times the amount required to replace the iron losses and prevent anemia in males even though it is listed as only 50% of the Daily Value. Ferrochel(tm) is in a form that is more readily used by the body and is many times more effective than ferrous sulfate. Rathe!
r than looking only at the milligram amounts of nutrients and the percent daily value (%DV), it is important to determine the quality of ingredients included in a supplement.

Again, the benefits of vitamin supplements cannot be measured by dosage alone. In fact, vitamins that are provided as natural food complex supplements are typically of a low dose, which may lead some people to believe they are not as potent or valuable. Adding to the confusion in comparing vitamin supplements is the fact that whole food vitamins do not fit the labeling model used by the FDA. The FDA's product labeling regulations were designed with only the cheaply produced, fractionated synthetic vitamins in mind. Whole food vitamins, which provide the complete vitamin complex, simply don't fit the FDA's archaic model.

The good news is that the labeling laws do allow the consumer to easily distinguish between a natural, whole food supplement and a synthetic supplement. Only a natural, whole food supplement will show the nutrient rich, natural food source from which the vitamins are derived, such as green pepper, acerola cherry and wheat grass. Don't be fooled by synthetic products that list high milligram amounts of vitamins. The label may look impressive, but they are not complete nutrients, will not be fully utilized in the body and your precious money spent on that product may literally get flushed down the toilet. Whole food vitamins provide the vitamin with all of its cofactors as nature intended it and will be absorbed and used by the body far more effectively.

"Natural" or "whole food" refers to vitamins as found in natural foods, unaltered in any way that might change their molecular, biological or biochemical combinations, or their action. You should see listed on the label the exact food source from which that vitamin is obtained. It will either be listed in parentheses next to the vitamin with its declared %DV or, more commonly, it will be listed in a "Proprietary Blend" in the lower section of the supplement facts label.

Choosing natural, whole-food vitamin supplements will ensure that you get the entire vitamin complex, not just the isolated fraction that science identifies as the 'vitamin.' For example, science has identified ascorbic acid as vitamin C and for vitamin E, it is alpha-tocopherol. Many people think that if you supply the body with these simplified synthetic or fractionated vitamins in the amounts specified by the RDA, you provide all the 'nutrition' required for health. That is why the vast majority of vitamin products on the market provide only ascorbic acid as Vitamin C, and only provide alpha-tocopherol as Vitamin E.

The problem with this idea is it does not take into consideration all of the enzymes, precursors, coenzymes, antioxidants, trace elements, activators and numerous other naturally occurring synergistic nutrients that we may or may not know about at this time. These other elements are a vital part of the complete vitamin complex and are required for the vitamin to be used by the body.

Imagine if we likened a vitamin to a car. If you analyze a car it doesn't take long to realize that most of the "action" takes place in the engine. Does this mean that we can eliminate all the other components of a car - the tires, seats, steering wheel, brakes, car body, etc. - and still have an good mode of transportation? Absolutely not! Although the majority of the "action" may take place under the hood, all the components of a car are necessary for a safe and effective mode of transport. Similarly, although ascorbic acid may be the most "active" component of a Vitamin C complex, all the other components are required for a completely safe and effective Vitamin C.

Quality is achieved by providing bioavailable vitamins and minerals that result in true cellular nutrition."