Dietary Supplements and Bioavailability: Does Size Matter?

“Many organizations are investigating how particle size and nanosizing may improve bioavailability,” says Federico Franceschi, PhD, a senior scientist from Indena S.p.A.

“Nanotechnology may well solve a lot of bioavailability problems,” says George Burdock, PhD, president and founder of Burdock Group. “For example, only about 17% of an orally administered dose of vitamin E is absorbed; however, when converted into nanoparticles, 100% of the dose will be absorbed because as nanoparticles, the particles are very, very small, and they can actually pass through or even between cells. Once absorbed, as a nanoparticle, it will also be easier to reach the target site within the cell.”

Many factors can inhibit absorption in the gastrointestinal tract, such as the acidity of a substance, the presence of highly charged constituents of a molecule, and solubility in cell membranes, adds Burdock. But with nanotechnology, these challengers “now take a backseat to the fact that the particle is so very small,” he says.

Microencapsulation may also improve bioavailability by altering the surface properties of a material. “For example, if you can encapsulate a fat-soluble vitamin such as vitamin E in a water-soluble coating, you increase its solubility-and its bioavailability,” says Bernadine Magnuson, senior scientific and regulatory consultant for Cantox Health Sciences International (Mississauga, ON, Canada).

But just because these technologies can be used to enhance bioavailability, should they be? “That is a question that’s compound-by-compound dependent,” says Magnuson. “If you have a compound that has a very good record of safety and beneficial properties, it could be quite advantageous. In other situations, perhaps there would need to be more due diligence. For example, if we’re talking about some of the vitamins such as vitamin A, which has known toxicities at certain levels, then the question of whether these technologies could be a good thing would have to be evaluated. If you’re going to increase the bioavailability several fold, you’d need to look fairly carefully at how close you’re coming to a level that could potentially have adverse effects.”

“The big disadvantage to nanoparticles is that they have the potential to be very toxic, in at least three ways,” says Burdock. “One, where the substance may have been marginally bioavailable and maybe require many hours for all of it to be absorbed, as a nanoparticle, it may be absorbed instantly. A quick absorption may have toxic effects-just like some substances are not toxic [when taken] orally because they are absorbed so slowly but that can be toxic if injected. Two, some substances exhibit different properties at the nanoparticle level, and formerly nontoxic substances could now become toxic. And three, the substance might become too bioavailable and get into places unavailable to it before, like the brain, or it could gain access to the fetus.”

“The bottom line-because substances have the potential to act differently at the nano level, they should be tested in animals before given to humans,” he concludes.

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