Clinical trials on curcumin in relation to its bioavailability and effect on malignant diseases: critical analysis

Curcumin is an ingredient of the root Curcuma longa, which is responsible for the characteristic yellow color of curcuma. Curcumin is said to have the potential ability to fight malignant diseases and to have an anti-inflammatory effect. In addition, it is used as a dietary supplement. However, one problem with the use of curcumin is its extremely low bioavailability. The aim of this study is to systematically review and critically analyze clinical studies related to the pharmacokinetics (or bioavailability) and to the use of curcumin in the treatment of malignant diseases. The platforms clinicaltrials.gov and PubMed served as the database for the literature research. A total of 293 available studies on curcumin were filtered according to their focus (bioavailability, therapy of malignant diseases) and other criteria (study results, main substance, topic reference, existing disease/other research purpose, reference to malignant diseases). The studies were further analyzed regarding their outcome measures, their design (number of participants, randomization, placebo group, masking, ethical standards, sponsor, primary outcome measures, secondary outcome measures, study bias) and their findings. The analysis failed to convincingly demonstrate that curcumin has a significant, positive effect on the therapy of malignant diseases. Regarding the increase in bioavailability, positive results have been obtained, which are in proximity to the pharmaceutical industry. Independent studies could not achieve increased bioavailability of curcumin. The available reviews in the literature also do not provide convincing evidence for the efficacy of curcumin. Thus, at the time being, the use of curcumin in malignant diseases is not justified scientifically.