Onions, garlic and other members of the allium genus, such as leeks, chives, scallions and shallots, have been shown to have antimicrobial, radioprotective, antithrombotic, hypolipidaemic, anti-inflammatory, antiarthritic and hypoglycemic effects, as well as improving immune function. Epidemiological studies have demonstrated an association between increased consumption of allium vegetables and a reduction in many different types of cancer, including cancer of the breast, prostate, lung, endometrium, stomach, colon, bladder, esophagus, larynx, mouth, ovary, and liver, as well as melanoma, acute myeloid leukemia, and childhood acute leukemia.
Breast cancer-related effects of eating onions and garlic
Chives and garlic are good dietary sources of the lignan enterolactone. Postmenopausal women with breast cancer and a high intake of enterolactone have been found to be less likely to die from their breast cancer than those with a low intake. Enterolactone has also been found to increase the sensitivity of breast cancer cells to radiation, thereby potentially enhancing the treatment effects of radiotherapy.
Chives also contain kaempferol. Green onions (scallions) and leeks are excellent sources of beta-carotene. Green onions also contain zeaxanthin, vitamin C, and vitamin K. Chives also contain vitamin C. Red onions are a source of delphinidin. Garlic is an excellent source of ajoene, allicin, apigenin, diallyl disulfide, and diallyl trisulfide.
Quercetin has been shown to increase the effectveness of both Adriamycin (doxorubicin) and Taxol (paclitaxel) chemotherapy in multidrug resistant ER+/PR+ breast cancer cells, in part by eliminating cancer stem cells.
Numerous studies have shown that onions, garlic and their components inhibit proliferation, reduces migration and invasiveness, and induces apoptosis of cultured human breast cancer cells. Garlic has been shown to decrease DNA strand breaks induced by carcinogens, inhibit DNA and RNA synthesis and protein folding in breast cancer cells, retard the growth of breast cancer cells by causing cell cycle arrest and apoptosis, and suppress angiogenesis.
One large European study found that eating onions and garlic was associated with lower risk of breast cancer. Another large Italian population-based study found a relationship between the consumption of increasing intake of flavones and flavonols found in allium vegetables and a reduction in the risk of breast cancer. A study of women in Mexico City found that consuming more than one slice of onion per day was associated with reduced risk of breast cancer. A Korean study found an association between onion and garlic consumption and lower incidence of breast cancer. However, there were no clear associations found between breast cancer risk and the consumption of onions or of individual flavonols in a study of premenopausal women in the Nurses Health Study II.
The anti-carcinogenic effect of allium vegetables is attributed in part to organosulfur compounds, which are generated upon cutting or chewing of these vegetables. Although some of the anticancer benefits of garlic are retained after cooking or processing it, raw garlic appears to have the most benefits.
Garlic is a good source of apigenin, which has been shown to increase the effectiveness of Taxol. Garlic has also been shown to have protective effects against Adriamycin-induced heart damage. However, garlic supplements have been shown to reduce the clearance of the chemotherapy drug Taxotere (docetaxel) in some (typically, African-American) women, a result that might also hold for Taxol.