In studies on the effects of curcumin on various types of cancers, researchers often observed inhibitory effects only on specific types of cancer. One study attributed the lack of beneficial effects of curcumin on induced lung and breast carcinogenesis in animal models to the poor circulating bioavailability of curcumin. In the same study, the authors substantiated the significant inhibitory effects of topical curcumin on chemically induced tumors in mouse skin. It is generally recognized that the therapeutic effectiveness of curcumin is limited due to its poor absorption from the gastrointestinal tract. Oral doses result in only traces appearing in the blood, with most of the dose being excreted in the feces.

One study evaluated the efficacy of Bioperine®, a standardized extract of black pepper containing the alkaloid, piperine, in enhancing the bioavailability of curcumin in animal models and human volunteers 84 . Piperine is proven to enhance the circulating bioavailability of several drugs and nutrients.

In the animal model study, two identical groups of rats were selected, one group receiving piperine alone (20 mg/kg body weight) or curcumin (2 g/kg) followed by piperine (20 mg/kg). The pharmacokinetic profile was determined for both groups of animals. In the human study, ten healthy male volunteers participated in a randomized crossover trial to determine the comparative bioavailability and pharmacokinetic profile of curcumin (2 g) when given along with piperine (20 mg). The results of these studies are indicated in Figures 1 and 2.

The results obtained in this study demonstrate that Bioperine® enhanced the oral bioavailability of curcumin in both rats and humans at doses that were devoid of adverse side effects. However, certain differences between rats and humans with respect to curcumin were evident. Curcumin alone attained overall moderate serum concentrations over a 4 hr period in rats with peak levels occurring between 0.75 and 1 hr. In humans, when curcumin was given alone only negligible serum concentrations of curcumin were detectable and the serum concentration-time curve was almost flat. This difference may be due to the high oral dose employed in the rat (2 g/kg), whereas the human dose was about 60 times less, approximately 33 mg/kg. Curcumin serum concentrations reached zero at 5 hr in rats and at 3 hr in humans. Furthermore, in rats the addition of piperine resulted in a higher curcumin concentration than in humans (although for a short period) which took a relatively longer time to increase and then decline. In contrast, in humans the maximum concentration was attained earlier and then declined precipitously. The study shows that piperine enhances the serum concentration and bioavailability of curcumin in both rats and humans. The authors postulate that this effect is probably due to increased absorption of curcumin in the presence of piperine.