Tomatoes are a rich source of the carotenoids lycopene, alpha-carotene, and beta-carotene, as well as melatonin, the anthocyanidin delphinidin, and the flavanoids quercetin, fisetin and naringenin, all of which have been found to have anti-cancer activities. Tomatoes have been shown to have anti-oxidant, anti-inflammatory, antimutagenic, and cardioprotective properties. Increased intake of tomatoes is associated with decreased cardiovascular disease and reduced risk of heart attack. Tomato consumption has been found to be associated with reduced risks of cancer of the mouth, breast, lung, stomach, pancreas, prostate, colon, ovary, and endometrium. However, tomatoes or lycopene have been shown not to have significant anticancer effects on renal cell, uterine, ovarian, and bladder cancers.
Breast cancer-related effects of eating tomatoes
A number of studies have found an inverse association between breast cancer risk and increasing consumption of tomatoes, components of tomatoes, or vegetables that have high levels of carotenoids (including tomatoes). For example, one study comprising 84,805 postmenopausal women in the Women's Health Initiative Observational Study found that dietary α-carotene, β-carotene, and lycopene were each found to be inversely associated with the risk of ER+/PR+ breast cancer. Another study found that dietary carotenoids inhibit the cancer-promoting effects of both estradiol and genistein (the phytoestrogen found in soy), thereby reducing their harmful effect in hormone-dependent breast cancer. Studies of naringenin, a tomato flavanone, have shown that it also inhibits ER+ breast cancer cell growth and migration in the presence of estradiol. Delphinidin, an anthocyanin found in tomatoes, has been shown to block epidermal growth factor receptor (EGFR) signaling in breast cancer cells (EGFR is expressed at high levels in at least 30% of breast cancers and is associated with a poor prognosis). However, one large study found no association between dietary or plasma lycopene levels and the risk of breast cancer in middle-aged and older women.
Several studies of early-stage breast cancer survivors have found that higher levels of cartenoids in the blood are associated with both lower risk of break cancer recurrence and lower risk of a new primary breast tumor. Another study found that plasma levels of retinol (a form of vitamin A that is a by-product of β-carotene in the body) also are positively associated with breast cancer survival in postmenopausal women.
As noted above, tomatoes are a good dietary source of melatonin. Melatonin protects against breast cancer in several ways, including by reducing aromatase activity within the breast, thereby reducing estrogen production.
Several studies have shown that the cardioprotective effect of tomatoes and lycopene extends to reducing the impact of myocardial toxicity from Adriamycin (doxorubicin) chemotherapy by ameliorating cardiac cell injury.
Cherry tomatoes rank the highest of all tomatoes in lycopene and overall antioxidant content, presumably because of their high ratio of tomato skin to tomato flesh and rich color. However, lycopene is absorbed in greater quantities from cooked tomatoes than fresh tomatoes. The best sources of bioavailable lycopene are tomato paste and tomato sauce. Frying greatly reduces the lycopene content of fresh tomatoes. While tomato ketchup has a relatively low overall carotenoid content compared to fresh tomatoes or tomato sauce, it is a good source of lycopene. However, note that high fructose corn syrup is the second most abundant ingredient in regular ketchup and that versions without this ingredient are available.
Ready-made tomato soups can have high levels of sodium nitrite, a known carcinogen. Check the labels of canned or otherwise pre-made soups and avoid those containing sodium nitrite. The table salt content of such soups can also be acceptably high for those who must limit their sodium intake.
Beta carotene, vitamin A and lycopene should be obtained from food rather than supplements. Generally speaking, synergistic interactions between the biologically active components in a given fruit or vegetable are important to its potential health-related characteristics. Supplementation by β-carotene and lycopene both have been found to be ineffective in reducing the risk of breast cancer. In addition, β-carotene supplementation has been linked to increased risk of lung cancer in high-risk persons and high serum β-carotene concentrations (presumably also resulting from supplementation) have been associated with increased risk of aggressive prostate cancer.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on tomatoes.