Turmeric

Turmeric (Curcuma longa) is a perennial rhizomatous herb 0.6–1.5 m tall in the ginger family (Zingiberaceae). Its oblong-lanceolate leaves, 30–45 cm long, rise in rows from a pseudostem, and small pale-yellow flowers form a cylindrical spike in the leaf axils. The harvested part is the orange rhizome, a branching underground stem whose colour comes from curcuminoids. The plant grows vigorously in the rainy season and dies back to a dormant rhizome in the dry season, favouring a tropical climate of 20–30 °C with 1,500–2,500 mm of rain per year.

According to Plants of the World Online (Kew), turmeric is treated as a cultigen originating in southwestern India and now spread throughout the tropics and subtropics. India dominates with roughly 75–80% of world output, mainly in Andhra Pradesh, Telangana, Tamil Nadu and Karnataka; other significant producers include Bangladesh, China, Indonesia, Thailand, Myanmar, Nigeria and Vietnam. Turmeric prefers loose, organic-rich, well-drained sandy loam and cannot tolerate waterlogging.

The main active constituents are curcuminoids, making up 2–5% of the dried rhizome: curcumin (about 60–70% of total curcuminoids), demethoxycurcumin and bisdemethoxycurcumin — the trio responsible for the yellow colour and the antioxidant and anti-inflammatory activity. The essential oil accounts for 1–3% and is rich in sesquiterpenes such as ar-turmerone, α- and β-turmerone and zingiberene, which give the warm aroma. The rhizome also contains starch, polysaccharides, fibre and minor phenolics. Curcumin is fat-soluble but almost insoluble in water and is rapidly metabolised, so its oral bioavailability is very low.

Turmeric is both the colouring spice of curry powder and many Asian dishes and a medicine of Ayurveda and traditional Chinese medicine used for millennia. Curcumin has been studied extensively: a meta-analysis of randomised controlled trials (Ferguson et al., 2024) found that curcumin supplementation lowered the inflammatory markers CRP, IL-6 and TNF-α and improved endothelial function, while a GRADE-assessed dose–response meta-analysis (Dehzad et al., Cytokine, 2023) reported antioxidant and anti-inflammatory effects. A review by Kunnumakkara et al. (ACS Pharmacology & Translational Science, 2023) compiled more than 400 clinical studies of curcumin in chronic disease. Because absorption is poor, newer formulations (phytosome, nanoparticles, piperine combinations) have been developed to raise bioavailability (Hegde et al., ACS Omega, 2023).

At culinary doses turmeric is considered safe; high supplemental doses may cause digestive upset and rare reports of liver injury, so caution is advised with anticoagulants or before surgery. For conservation, Curcuma longa was assessed as Data Deficient (DD) by the IUCN in 2021 and is predicted not to be threatened with extinction (Bachman et al., 2024); as a globally cultivated crop, conservation priorities centre on maintaining local landraces and wild genetic resources in its area of origin.