Medicinal properties of turmeric (Curcuma longa L.), a plant used for centuries as an anti-inflammatory, are attributed to its polyphenolic curcuminoids, where curcumin predominates. Although “curcumin” supplements are a top-selling botanical with promising pre-clinical effects, questions remain regarding biological activity in humans. To address this, a scoping review was conducted to assess human clinical trials reporting oral curcumin effects on disease outcomes. Eight databases were searched using established guidelines, yielding 389 citations (from 9528 initial) that met inclusion criteria. Half focused on obesity-associated metabolic disorders (29%) or musculoskeletal disorders (17%), where inflammation is a key driver, and beneficial effects on clinical outcomes and/or biomarkers were reported for most citations (75%) in studies that were primarily double-blind, randomized, and placebo-controlled trials (77%, D-RCT). Citations for the next most studied disease categories (neurocognitive [11%] or gastrointestinal disorders [10%], or cancer [9%]), were far fewer in number and yielded mixed results depending on study quality and condition studied. Although additional research is needed, including systematic evaluation of diverse curcumin formulations and doses in larger D-RCT studies, the preponderance of current evidence for several highly studied diseases (e.g., metabolic syndrome, osteoarthritis), which are also clinically common, are suggestive of clinical benefits.

While the chemotherapeutic effect of curcumin, one of three major curcuminoids derived from turmeric, has been reported, largely unexplored are the effects of complex turmeric extracts more analogous to traditional medicinal preparations, as well as the relative importance of the three curcuminoids and their metabolites as anti-cancer agents. These studies document the pharmacodynamic effects of chemically-complex turmeric extracts relative to curcuminoids on human breast cancer cell growth and tumor cell secretion of parathyroid hormone-related protein (PTHrP), an important driver of cancer bone metastasis. Finally, relative effects of structurallyrelated metabolites of curcuminoids were assessed on the same endpoints. We report that 3 curcuminoid-containing turmeric extracts differing with respect to the inclusion of additional naturally occurring chemicals (essential oils and/or polar compounds) were equipotent in inhibiting human breast cancer MDA-MB-231 cell growth (IC₅₀=10-16µg/mL) and secretion of osteolytic PTHrP (IC₅₀=2-3µg/mL) when concentrations were normalized to curcuminoid content. Moreover, these effects were curcuminoid-specific, as botanically-related gingerol containing extracts had no effect. While curcumin and bis-demethoxycurcumin were equipotent to each other and to the naturally occurring curcuminoid mixture (IC₅₀=58µM), demethoxycurcumin did not have any effect on cell growth. However, each of the individual curcuminoids inhibited PTHrP secretion (IC₅₀=22-31µM) to the same degree as the curcuminoid mixture (IC₅₀=16µM). Degradative curcuminoid metabolites (vanillin and ferulic acid) did not inhibit cell growth or PTHrP, while reduced metabolites (tetrahydrocurcuminoids) had inhibitory effects on cell growth and PTHrP secretion but only at concentrations ≥10-fold higher than the curcuminoids. These studies emphasize the structural and biological importance of curcuminoids in the anti-breast cancer effects of turmeric and contradict recent assertions that certain of the curcuminoid metabolites studied here mediate these anti-cancer effects.

Objective: Scientific evidence is lacking for the antiarthritic efficacy of turmeric dietary supplements that are being promoted for arthritis treatment. Therefore, we undertook studies to determine the antiarthritic efficacy and mechanism of action of a well‐characterized turmeric extract using an animal model of rheumatoid arthritis (RA).Methods: The composition of commercial turmeric dietary supplements was determined by high‐performance liquid chromatography. A curcuminoid‐containing turmeric extract similar in composition to these supplements was isolated and administered intraperitoneally to female Lewis rats prior to or after the onset of streptococcal cell wall–induced arthritis. Efficacy in preventing joint swelling and destruction was determined clinically, histologically, and by measurement of bone mineral density. Mechanism of action was elucidated by analysis of turmeric's effect on articular transcription factor activation, microarray analysis of articular gene expression, and verification of the physiologic effects of alterations in gene expression.Results: A turmeric fraction depleted of essential oils profoundly inhibited joint inflammation and periarticular joint destruction in a dose‐dependent manner. In vivo treatment prevented local activation of NF‐κB and the subsequent expression of NF‐κB–regulated genes mediating joint inflammation and destruction, including chemokines, cyclooxygenase 2, and RANKL. Consistent with these findings, inflammatory cell influx, joint levels of prostaglandin E₂, and periarticular osteoclast formation were inhibited by turmeric extract treatment.Conclusion: These translational studies demonstrate in vivo efficacy and identify a mechanism of action for a well‐characterized turmeric extract that supports further clinical evaluation of turmeric dietary supplements in the treatment of RA.