Some people find it nearly impossible to obtain all of the nutrients they need from a regular diet, which is why each year Americans spend billions of dollars on nutritional and health supplements.

What they may not realize, however, is that many supplements are so densely packed that their bodies cannot properly absorb all of the nutrients or fully break down the vitamin. Some vitamins also are wrapped in a coating that inhibits the absorption of the nutrients into the body, doctors say.

Supplements should dissolve in about 30 minutes in order for the body to absorb the full amount of nutrients, said Dr. John P. Mamana, who practices internal medicine at Virginia Medical Alliance and teaches at Georgetown University School of Medicine. But a simple at-home test reveals that some of the most popular vitamins can take several hours, even days, to fully dissolve.

To try this experiment, combine equal parts of warm water and white vinegar. Then drop the supplement into the mixture, gently stirring the water every few minutes. The pH of vinegar is similar to that of stomach acid, so the reaction should replicate what will happen when you take the supplement.

The failure of supplements to dissolve properly not only leaves the body lacking in nutrition, but it wastes money since most undigested vitamins simply pass through the body. It can result in health troubles as well. Mamana says consumers often experience constipation, indigestion and general discomfort after taking such a vitamin.

"Our active bodies need the highest quality nutrients available, with the ability to easily absorb them," he said.

With this in mind, companies such as American Health Sciences have developed supplements that dissolve within 30 minutes. American Health Sciences worked with a team of over 30 physicians and scientists to create its pharmaceutical-grade line of supplements, Clinician's Choice. These toxin-free supplements efficiently deliver essential vitamins and minerals directly to where the body needs them, according to the company.