Nature's Pharmacopeia: A World of Medicinal Plants
Originating in South and Southeast Asia, turmeric is an herbaceous perennial now cultivated throughout the tropics. It grows to a height of about 1 meter, composed of numerous 50-centimeter-long flat, green, sword-shaped leaves and a spike of leaves and tubular pale-yellow flowers each about 5 centimeters in length. The underground portion, called the root, consists of a rhizome and roots that are used in cuisine, dyes, and medicine. Long valued in South Asia, the rhizome can grow to about 3 centimeters in diameter and 6 centimeters or more in length, and its orange-yellow flesh is eaten fresh, ground for use in flavoring dishes (turmeric being a key component of curries, for example), taken in medicinal food or herbal teas, and used as a pigment to color paper and textiles (figure 14.25).189
Widely esteemed for health-related properties in the traditional and folk medicines of Asia, its ancient use is evidenced in the written lore of India and China. At the inception of one of the major South Asian medical traditions, an ancient Sanskrit text suggests turmeric to treat the skin, slow graying hair, and—perhaps because of its color—ward off jaundice.190 In China, turmeric first appeared in a seventh-century medical treatise, considered a warming herb capable of invigorating the blood and driving qi downward. Later, in 1596, the author Li Shizhen recommended turmeric to treat obstructions of qi and relieve pain.191
FIGURE 14.25 Turmeric root: (left) fresh; (right) dried and scraped; (center) ground.
Turmeric entered the western European pantry during medieval times, considered a cheaper substitute for another precious imported spice: the brightly colored, subtly flavored female structures of the Near Eastern saffron crocus flower (Crocus sativus).192 Turmeric was little employed in European medicine, where many considered it less potent than its botanical relative ginger (Zingiber officinale) and useful only as a dye.193 Perhaps it is not surprising that Europeans found more value in turmeric as a pigment than as a medicine or spice because the combination of volatile oils and polyphenolic chemicals in the rhizome are liable to dissipate and become modified over time, which explains why freshly prepared turmeric is preferred by those seeking its flavor, aroma, and other health-related effects.194
The essential oil of turmeric makes up about 6 percent of the weight of the rhizome and contributes to the scent and flavor of the herb; a set of polyphenols (accumulating to 5 percent) collectively called curcumin is responsible for much of the color.195 Curcumin is also thought to be responsible for many of turmeric’s perceived medicinal effects. Considerable research has accrued in recent decades that shows curcumin to have numerous possible therapeutic targets.
In laboratory tests, curcumin polyphenols demonstrate antioxidant and anti-inflammatory properties, which might recommend them for age-related degenerative concerns and cancers.196 Curcumin displays anti-inflammatory activity by suppressing a suite of enzymes that propagate pro-inflammatory signals and by blocking the expression of a key gene responsible for inflammation, cell proliferation, and other aspects of chronic disease.197 The capacity to interfere with the inflammatory processes suggests curcumin as a possible agent against, for example, rheumatoid arthritis and inflammatory bowel disease. It might also be of value in promoting wound healing and treating skin problems.198 Furthermore, curcumin’s inhibition of genes that regulate cell division make it an appealing candidate for the treatment of cancers, which are characterized by abnormal cell proliferation.199 While active investigations in other areas seek to demonstrate whether curcumin might be a good candidate as a neuroprotectant, an antiviral, a cardiovascular protectant, and the like, few clinical trials have addressed its speculated therapeutic effects.200
One factor that may complicate curcumin’s transition from laboratory to clinic is its hydrophobic nature (poor ability to dissolve in water). As a simple turmeric extract taken by mouth, very little of a curcumin dose passes into the bloodstream. There are some additives that might aid its uptake, but they are in the exploratory stages.201 To render the active principles more effective, chemists have suggested altering the fundamental structure of the molecules into more water-soluble derivatives.202 With the knowledge of thousands of years of traditional culinary and health practices, the experimental data of curcumin’s prospects in the laboratory, a rational basis for modifying select compounds for increased activity, and a growing body of clinical literature, much more remains to be written on turmeric’s medicinal legacy.