Turmeric is a plant prevalent in South Asia, and is now cultivated in tropical areas around the world. The rhizome is used as a spice in regional cuisines, and as a coloring agent in food and cosmetics for its yellow-orange color. It is also used in traditional medicine for improving circulation and digestion. Turmeric extracts are marketed as dietary supplements to improve memory, for arthritis, and for cancer prevention.

The active constituents are turmerone oil and water-soluble curcuminoids, among which curcumin has largely been the focus of research. In vitro studies suggest that it acts as a weak phytoestrogen ⁽¹⁾, and exhibits neuroprotective ⁽²⁾, choleretic ⁽³⁾, anti-inflammatory ⁽⁴⁾, immunomodulatory ⁽⁵⁾, anti-proliferative ⁽³⁾, and chemopreventive effects ^{(6) (7) (8)}. Curcumin, its analogs, and liposomal formulations also demonstrated chemosensitizing ^{(9) (10) (11)} and radiosensitizing effects ^(12) (13).

Turmeric and its active constituents have been studied extensively. Clinical findings indicate that it may be effective against major depressive disorder  ⁽⁶²⁾, and epidemiological data suggest improved cognitive performance in elderly Asians who consumed turmeric in the form of curry powder ⁽¹⁴⁾. However, there were no benefits of curcumin supplementation in patients with Alzheimer’s disease ⁽¹⁵⁾. Turmeric may also help alleviate gastrointestinal symptoms  ⁽⁸¹⁾; symptoms of irritable bowel syndrome  ⁽¹⁶⁾ and quiescent ulcerative colitis ⁽¹⁷⁾. But in  patients with familial adenomatous polyposis, there was no reduction in lower intestinal tract adenomas with long-term use of curcumin ⁽⁷⁰⁾.

Turmeric may help reduce arterial stiffness in patients with type 2 diabetes mellitus ⁽⁷⁷⁾ and benefit children and adolescents with asthma ⁽⁷⁸⁾. It was also found to be safe and as effective as paracetamol ⁽⁸²⁾ or a non-steroidal anti-inflammatory drug ⁽¹⁸⁾ for the treatment of osteoarthritis of the knee, but did not affect knee effusion-synovitis or cartilage composition ⁽⁸³⁾.

Supplementation with curcumin may be useful in managing sarcopenia in older subjects ⁽⁸⁴⁾. But it is not known whether it increases cholesterol levels, as available data are mixed ^(19) (20). In a study of postmenopausal women, consumption of curcumin, along with aerobic exercise training, improved vascular endothelial function ⁽⁶¹⁾. Findings of a systematic review suggest that supplementation with turmeric or curcumin may benefit patients with non alcoholic fatty liver disease by positively affecting serum concentrations of liver enzymes ⁽⁷⁵⁾. Preliminary findings suggest benefits of combining curcumin with antipsychotics for controlling symptoms in patients with chronic schizophrenia ⁽⁷⁹⁾.

Turmeric has also been studied in cancer patients. Oral curcumin administered to colorectal cancer patients during the pre-surgery waiting period improved cachexia ⁽²¹⁾. In a phase II trial of oral curcumin in patients with advanced pancreatic cancer, clinically relevant biological activity was seen in two patients despite limited absorption ⁽²²⁾. Preliminary data also suggest that turmeric supplementation during capecitabine treatment may reduce rates of hand-foot syndrome  ⁽⁷¹⁾. Supplementation with a blend of green tea, pomegranate, broccoli and curcumin resulted in a reduction in the rate of prostate-specific antigen (PSA) increase among men with prostate cancer following a PSA relapse post-radical treatment ⁽⁶⁵⁾.

In early phase studies, curcumin combined with docetaxel ⁽²³⁾ and gemcitabine ^(24) (25) was found to be safe, but a high dose of curcumin was needed to achieve systemic effect ^(23) (25). Also, in a study of patients with metastatic colorectal cancer, curcumin was reported to be a safe and tolerable adjunct to FOLFOX chemotherapy ⁽⁷²⁾.
Supplementation with turmeric improved quality of life and hematological parameters in breast cancer patients  ⁽⁸⁵⁾.

Preliminary studies in head and neck cancer patients suggest effectiveness of a topical turmeric-based cream for reduction of radiotherapy-induced dermatitis ⁽⁶⁴⁾, and of a curcumin mouthwash to delay the onset of radiation induced oral mucositis ⁽⁸⁶⁾. Topical application of turmeric or curcumin was also found useful for controlling signs and symptoms of oral mucositis ⁽⁷⁶⁾. In addition, curcumin, combined with hydroxytyrosol and omega-3 fatty acids, may help reduce inflammation and pain in early breast cancer patients with aromatase-induced musculoskeletal symptoms ⁽⁸⁰⁾.

Curcumin is known to interfere with cytochrome P450 enzymes ^(26) (27) and may interact with chemotherapy drugs like cyclophosphamide and doxorubicin ⁽²⁸⁾. Overall, the development of turmeric for clinical use needs further investigation due to its inherent poor absorption, rapid metabolism, complex mechanistic profile, and largely preclinical data.