Papaya leaf extract has not been shown to treat or prevent cancer.
Papaya tree is common to many tropical regions of the world. Papaya leaves and their extracts are sold as dietary supplements to improve immune system, platelet counts, and to prevent side effects of chemotherapy. Laboratory and animal studies show that papaya leaf extracts can stop growth of a variety of bacteria, improve platelet count, and reduce stomach damage caused by alcohol. Human studies have not been conducted.
Papaya tree is commonly found in tropical areas around the world. The fruits are consumed as food and as medicine; dried and powdered stem and leaves are used to prepare medicinal teas against infections and to improve digestion. Papaya leaves and their extracts are also marketed as dietary supplements to enhance the immune system, to improve platelet function, and to prevent chemotherapy-related adverse effects.
Papaya leaves exhibit antitumor, immunomodulatory (1), and antioxidant (9) effects in vitro. The leaf extracts contain antibacterial compounds that inhibit the growth of a wide variety of Gram-positive and Gram-negative bacteria (4).
In mice, a powdered suspension of papaya leaves increased thrombocyte count (2) and a water extract reduced alcohol-induced stomach damage (5). Hypoglycemic effects were also reported with use of papaya leaf extract in streptozotocin-induced diabetic rats (10).
According to a case report, a water extract of papaya leaves was shown to increase the platelet count of a patient with Dengue fever (3).
Papaya leaf extract showed low toxicity (6) in an animal model, but it has not been studied in humans. An international patent has been filed for its use in increasing low platelet counts (7). Papaya leaf extracts should not be used as a treatment for cancer or for low platelet count until more is known about its efficacy and adverse effects in humans.
Papaya leaf extract modulates the immune system by enhancing the production of Th1 type cytokines, such as interleukin (IL-12), interferon (IFN-gamma) and tumor necrosis factor (TNF-alpha). Fractions with molecular weight less of than 1000 are most active in inhibiting tumor cell growth (1). Papaya leaf extract also has antioxidant effects (5) and contains antibacterial and phenolic compounds (6)(8) but the mechanism of action remains unclear.