Does Turmeric Essential Oil Enhance Curcumin Bioavailability? A Critical Review of the Human Pharmacokinetic Evidence and Its Implications for Curcuma Nutraceuticals

Abstract

Abstract

Reviews of Curcuma essential oils catalogue many biological activities of turmerones, and a recent review states that adding turmeric oil increases curcumin bioavailability 6.93- to 8.2-fold. This review appraises the human evidence behind that claim. Six human pharmacokinetic studies of curcumin formulations containing turmeric oil or turmerones were identified. Every study favoured the product of its sponsor. The study sponsored by the oil-formulation manufacturer reported a 6.93-fold increase, whereas two randomised, double-blind crossover studies analysed by mass spectrometry found 1.1- to 1.3-fold increases after dose normalisation, and two further studies ranked oil formulations below competing products. The two manufacturer studies reported curcumin peaks of 1.2 to 1.8 µM without separating conjugated from unconjugated curcumin, roughly 600 to 900 times higher than independent measurements of unconjugated curcumin. The 8.2-fold figure traces to an unpublished document. After a 360 mg dose, plasma ar-turmerone peaked at 3.38 ng/mL, 650 to 1540 times below the concentrations at which it acts in vitro. Current evidence does not support the claim that turmeric oil substantially enhances curcumin bioavailability. Product claims should be withdrawn or tested in independent, factorial trials that measure unconjugated curcumin.