Alfalfa (also known as lucerne or purple medic) is a perennial legume of the pea family, native to western Asia and the eastern Mediterranean region and cultivated throughout much of Europe, North America, and South America. The plant has an erect stem growing 40 to 90 centimeters tall, and grayish-green, clover-like leaves. Alfalfa flowers throughout much of the summer, bearing clusters of small, blue or purple flowers, which produce coiled pods containing multiple seeds. Perhaps the most remarkable attribute of alfalfa is its extremely deep root system, which may reach depths as great as 15 meters in porous subsoil. After just five months of growth, the tap root may reach as deep as two meters. Cultivated primarily for hay and silage, alfalfa has a remarkable capacity for rapid regeneration of stems and leaves after cutting, allowing several crops of hay in one growing season.
A rich source of protein, fiber, and vitamin K, alfalfa also contains carotenoids (especially lutein), saponins, isoflavonoids (including glycosides, genistein, and diadzein), triterpenes, coumarins, glycosides, fatty acids, and betaine.
No therapeutic dosage of alfalfa has been established for humans. Consumption of alfalfa leaves and seeds have not been associated with any toxicity. Alfalfa sprouts have induced symptoms of systemic lupus erythematosus (SLE) in lab experiments, apparently due to the action of L-canavanine, an amino acid found in alfalfa seeds and sprouts. In vitro studies indicate that L-canavanine influences the activity of immunoregulatory cells, which may account for lupus-inducing activity. Consequently, many herbalists recommend that people with SLE avoid alfalfa products. In recent years, consumption of fresh alfalfa sprouts, a popular ingredient in salads and sandwiches, has been associated with outbreaks of Salmonella and E. coli infections. Until effective measures are found to prevent sprout-associated disease, people who wish to reduce their risk for food-born illnesses (in particular, the elderly, children, people with compromised immune systems, and others at risk for severe complications of E. coli or salmonella infection) should not eat raw sprouts.