Curcumin Supplementation and Human Disease: A Scoping Review of Clinical Trials

Abstract

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.

Keywords: Curcuma longa L.; curcumin; curcuminoids; dietary supplement; human clinical trials; turmeric.

Figure 1

Chemical structures of turmeric-derived curcuminoids, of which curcumin is the most abundant.

Figure 2

Preferred Reporting Items for Systematic Reviews (PRISMA) flow diagram of scoping review process used to search literature and extract citations meeting inclusion criteria.

Figure 3

Turmeric clinical trials by organ system or disease process. Clinical trials were organized for analysis by organ system (e.g., musculoskeletal [MSK], neuropsychiatric [NEURO], gastrointestinal [GI], cardiovascular [CV], oral mucosa, renal, reproductive organs [REPRO], pulmonary [PULM], or dermatologic [DERM] disorders) or disease process (metabolic disorders including non-alcoholic fatty liver disease [METABOLIC + NAFLD] or cancer [CA]).

Figure 4

Publication timeline for curcumin clinical trials. Citations per year are presented in stacked plots to demonstrate secular trends for the five most common categories, including metabolic (with NAFLD graphed separately), musculoskeletal (MSK), neuropsychiatric (NEURO), and gastrointestinal (GI, excluding NAFLD) disorders or cancer [CA]. All other diseases (OTHER) are graphed as a group.

Figure 5

Curcumin clinical trial design elements by disease category. (A) Prevalence of citations reporting double-blind, randomized, placebo-controlled (D-RCT) trial results. (B) Curcumin clinical trial duration or (C) size, noting individual citations (open circles) and averages (red line). (D) Prevalence of citations reporting enhanced bioavailability curcuminoid product treatment effects.

Figure 6

Frequency of specific conditions studied within each of the top five categories, which together accounted for 75% of curcumin clinical trial citations. N = number of citations.