Turmeric (Curcumin)

Turmeric is the rhizome of Curcuma longa, a plant in the ginger family cultivated across South Asia. It has been used as both food and traditional medicine for thousands of years, and gives curry powder its colour.

The compounds of interest are curcuminoids, principally curcumin. Raw turmeric root contains only around 2 to 5 per cent curcuminoids by weight, which is why eating turmeric and taking a curcumin extract are not remotely the same thing. A standardised extract is typically 95 per cent curcuminoids.

Absorption is the central problem and the reason this category is so crowded with branded formats. Curcumin is poorly water soluble, poorly absorbed, rapidly metabolised and quickly cleared. Phospholipid complexes, nanoparticle preparations, liposomal formats and piperine combinations all exist to address this, and they are not marketing padding — the difference in plasma levels between plain curcumin and an enhanced format is substantial.

Curcumin acts on a broad range of signalling pathways rather than a single target. The most studied is NF-kB, a transcription factor that switches on genes involved in the inflammatory response. Curcumin appears to dampen its activation, which is the basis for most of the research interest.

It also influences the enzymes that produce inflammatory signalling molecules, and has direct antioxidant activity alongside effects on the body's own antioxidant defence systems.

This breadth is both the appeal and the difficulty. A compound that touches dozens of pathways in a laboratory dish is interesting, but it also makes it hard to predict what it does in a person at achievable plasma concentrations — which, for plain curcumin, are very low indeed.

Joint comfort in active adults is among the better-supported areas, with several trials reporting improvements in reported stiffness and comfort scores over 8 to 12 weeks. Effect sizes are modest, and results are considerably more consistent in trials using enhanced-absorption formats.

Exercise-induced muscle soreness is a smaller but reasonably encouraging area, with trials reporting reduced soreness and lower markers of muscle damage in the days after hard training.

The wider literature is enormous and much of it is preclinical. Curcumin has been flagged by chemists as a compound that produces misleading positive results in laboratory assays, which is a fair reason to weight human trials heavily and treat cell-culture findings with scepticism. Where the human data holds up, it does so at doses using absorption-enhanced preparations.

Turmeric has an excellent safety record as a food and is well tolerated as a supplement. Digestive upset, nausea and loose stools are the most common complaints, generally at higher doses.

Curcumin has a mild effect on how readily blood clots and stimulates bile flow, so check with your doctor before use if you take regular medication or have been told there is a problem with your gallbladder.

Concentrated extracts are a different proposition from turmeric in food, and reports of liver-related adverse effects have appeared, most often with high-dose enhanced-absorption products. Stop and seek advice if you notice yellowing of the skin or eyes, unusually dark urine or unexplained fatigue.