Many liquid supplement manufacturers claim that because their product is in a liquid form it is more bioavailable. In fact, some even use phony statements regarding the
Physician's Desk Reference
to support such claims. The statement they reference about liquid supplements being more bioavailable first appeared in the PDR under a listing for a specific nutritional supplement product. That statement has since been removed because it could not be substantiated.
Nutrients are typically absorbed by the small intestine (unless they are taken sublingually or injected). When you ingest a supplement in either liquid or tablet form, it must first pass through the stomach before reaching the small intestine. If liquids were simply absorbed directly into the bloodstream, as some supplement companies claim, what would happen when individuals consumed soup? Would it also be absorbed directly into the bloodstream?
Bioavailability is defined as the degree and rate at which a substance (as a drug) is absorbed into a living system - or more correctly, the degree or rate at which it is ultimately made available at the site of physiological activity. Different vitamins and minerals have different absorption rates regardless of whether they come from a tablet, liquid, powder, or food. Calcium, for example, has a fairly standard absorption rate (25-35%), and the form does not generally make a significant difference.
A well-made tablet provides a very effective delivery system and is the chosen form of most pharmaceutical medications. This is because tablets have been confirmed, through years of carefully controlled studies, as a reliable and efficient delivery system for medications. Why would vitamin and mineral supplements be any different? Does anyone doubt that an aspirin tablet is ineffective because it comes in a tablet?
Tableted products can also provide an increased amount of active ingredient (almost 3x as much as a capsule and much more than a liquid or spray). In general, the stability of tablets is also superior to liquids.
Bioavailability is a complicated topic because it is not dependent solely on product formulation. Many external factors can affect the absorption of vitamins, minerals, and other compounds. Some of these factors are a function of the person taking the nutrient, including age, digestive system integrity, overall health status, the time of day, gender, and if the product is taken on a full or empty stomach. People whose nutrient needs are greater - such as growing children, pregnant or lactating women, and those who are currently deficient - may have significantly enhanced absorption rates for certain nutrients.
Recently, some individuals and companies have made claims that their products are superior because they are "98% absorbed" or some similar number. This is a misleading statement because there are far too many variables to imply that an individual's absorption is a certain percent of the material consumed. Even absorption of minerals from food sources can vary significantly. Boron, molybdenum, and iodine can be absorbed at over 90 percent, while the average absorption rates of zinc, copper, and selenium range from 30 to 80 percent depending on the form. As such, stating an absolute absorption rate on product packaging or advertising is almost always misleading.
USANA tablets are formulated to meet United States Pharmacopoeia standards, which require full disintegration within 30-45 min. They are also formulated to meet standards for dissolution. Innovative formulations have been developed to optimize nutrient bioavailability. Each lot of
USANA tablets is tested against finished product specifications to ensure that standards are met for identity, target weight, hardness, thickness, disintegration, potency, purity, and microbial counts.
The dietary supplement industry could not exist without rigorous, peer-reviewed studies that used tableted forms of vitamins and minerals to establish what we is now regarded as common nutritional knowledge. With thousands of studies connecting various vitamins and mineral supplements with markers of health, it is impossible to dispute the effectiveness of tablets as a delivery system. If tablets were ineffective, why have so many researchers observed positive results? If liquid or spray supplements are obviously superior, why are they rarely - if ever - used in published scientific research?
(Keep in mind that this article primarily addresses
multivitamin formulations. There may be certain products, such as children's medicines, that are more appropriate in liquid form. However, such products are the exception - not the rule.)
Finally, liquid supplement promoters often contend that liquids are better because they don't contain fillers (excipients used in tablets for disintegration, form, binding, coating, etc). This is perhaps the most illogical argument of all, since liquid supplements require many more "other" ingredients, including emulsifiers, solvents, preservatives, stabilizing agents, coloring, flavoring, and more. Generally speaking, the more vitamin and mineral ingredients there are in a liquid supplement, the more excipients that product will require.
