Studies have not established the effect of papaya on breast cancer
Papayas (Carica papaya) and their seeds contain substances that have been shown to have antihypertensive, antioxidant, anti-amoebic, antiparasitic, antiseptic, wound and burn healing, contraceptive and neuroprotective properties, as well as improving cholesterol profile and assisting with digestion. Papaya is a good dietary source of vitamin C and vitamin A (through its beta-carotene content). The fruit has been selected to raise levels of vitamin A in children in deficiency-prone countries such as Cameroon and Sri Lanka. Compounds with known cancer-fighting properties found in papayas include carotenoids such as lycopene, beta-carotene and cryptoxanthin, as well as several isothiocyanates. The benzyl isothiocyanate found in papaya has been shown to induce apoptosis in pancreas, prostate, and leukemic cancer cells and to inhibit carcinogen-induced bladder cancer.
Breast cancer-related effects of eating papaya
Benzyl isothiocyanate, found in papaya flesh and seeds, has been shown to selectively induce apoptosis in human breast cancer cells. The high carotenoid levels found in papayas suggest that consuming the fruit could serve to protect against breast cancer. However, no population studies have been performed that directly assess the effects of papaya on the risk of breast cancer.
Additional comments
Papayas are sometimes referred to as paw paws, but the paw paw (Asiminia triloba) sold in the U.S. is a different fruit. Papayas have two possible flesh colors, yellow and red. The red color of red papaya fruit is due to an accumulation of lycopene; the yellow color of yellow papaya is the result of conversion of lycopene to beta-carotene and beta-cryptoxanthin. Papayas should be eaten ripe, without the skin or seeds. Even though the peel is not eaten, papayas should be washed thoroughly before being cut up for consumption since potent pesticides typically are used in growing them.
Both raw and cooked green papayas (i.e., unripe papayas) are used in some Asian cuisines. For example, atchara, a Filipino condiment or side dish, is made of primarily of pickled raw green papaya. Ground papaya seeds are used in some cuisines similarly to black pepper. However, we recommend against consuming green papaya (whether raw, cooked or dried) or papaya seeds. Unlike ripe papaya, green papaya contains a high concentration of a type of latex that has been shown to produce uterine contractions in rats; this may be the basis for the belief in parts of Asia that consumption of papaya is unsafe during pregnancy. In fact, green papaya is used for female contraception and abortion in some traditional medicine systems.
Papaya seeds contain a higher proportion of benzyl isothiocyanate than does the flesh and they are sometimes used as part of herbal preparations. However, one study found that rats consuming papaya seed extract exhibited liver cell damage and precancerous liver changes in a dose-dependent manner. Another study found that benzyl isothiocyanate promoted urinary bladder carcinogenesis in rats. Papaya seed extracts also have been shown to have dose-dependent spermicidal effects, causing human sperm immobilization and death.
Dried papaya typically has been treated with sulfur dioxide to prevent the fruit from oxidizing during and after the drying process, thereby preserving its color. However, sulfur dioxide and its derivatives have been shown to increase the frequencies of chromosomal aberrations in mammalian cells and cause oxidative damage in multiple organs of male and female mice. Therefore, we recommend obtaining unsulfured dried fruit where possible.
Papain, a component of papaya found in some powdered meat tenderizers and some herbal supplements, has been shown to increase the effect of warfarin (coumadin) blood thinning therapy.
Note that while we are continually searching for new evidence specifically concerning this food, there is not much interest in it among breast cancer researchers, so few studies are available.