The Cancer Research
Early research connected tomatoes with reducing the risk of prostate cancer but the evidence for this link has weakened as the quality of research has improved. However, the complexities of the types and timing of this cancer’s development, and tomato amounts, forms and possible synergy with other foods, leaves many unanswered questions about potential benefits.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how non-starchy vegetables and their nutrients affect the risk of developing cancer.
Evidence categorized as “convincing” or “probable” means there is strong research showing a causal relationship to cancer—either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings.
- A convincing or probable judgment is strong enough to justify recommendations.
- Tomatoes are a non-starchy vegetable. There is probable evidence that non-starchy vegetables DECREASE the risk of:
- Mouth, pharynx, nasopharynx, larynx, esophagus, lung, stomach, and colorectal (aerodigestive) cancers
Evidence categorized as “limited suggestive” means results are generally consistent in overall conclusions. But because there’s not enough evidence or some limitations in the research, it’s rarely strong enough to justify using it as a basis for recommendations to reduce the risk of cancer.
- Limited evidence suggests that non-starchy vegetables may also DECREASE the risk of:
- estrogen receptor-negative (ER-) breast cancer
- bladder cancer
- Limited evidence suggests that foods containing beta-carotene may DECREASE the risk of
- lung cancer
- Limited evidence suggests that foods containing carotenoids may DECREASE the risk of:
- lung cancer
- estrogen receptor-negative ER- breast cancer
- Limited evidence suggests that foods containing vitamin C may DECREASE the risk of:
• Lung cancer (in people who smoke) and colon cancer
Ongoing Areas of Investigation
Laboratory research related to tomato, tomato compounds and cancer suggests several possible anti-cancer mechanisms.
- Carotenoids act as antioxidants and stimulate the body’s own antioxidant defenses, decreasing free radical damage to DNA that can lead to cancer. Very high levels in cell studies, however, can have an opposite effect, promoting damage from oxidation.
- Lycopene and compounds that form as it’s metabolized act as antioxidants in cell studies and activate the body’s antioxidant defenses. In cell studies, lycopene decreases cell growth and reproduction, increases self-destruction of abnormal cells and influences androgen hormones that can drive the development of prostate cancer.
- In numerous animal studies, lycopene protects against prostate cancer. Yet compared to lycopene alone, whole tomato powder links to even lower prostate cancer risk. The tomato powder includes other carotenoids and additional compounds. Several animal studies combining tomatoes and broccoli have also shown lower prostate tumor growth than with lycopene or tomatoes alone, suggesting compounds in these foods may work together.
- Beta-carotene promotes cell-to-cell communication that helps control cell growth and can stimulate self-destruction of abnormal cells. The body uses beta-carotene to form vitamin A, which helps protect against cancer through the immune system and expression of genes that regulate cell growth.
- Vitamin C is a powerful antioxidant. In lab studies, it protects cells’ DNA by trapping free radicals, and it helps renew the antioxidant ability of Vitamin E. In cell studies, vitamin C also inhibits the formation of carcinogens and supports the immune system.
AICR/WCRF’s latest expert report found strong evidence that people who eat more vegetables and fruits have lower risk of a wide range of mouth, pharynx and other aerodigestive cancers. This probably reflects combined protection from the many nutrients and compounds they contain. These plant foods may also help people stay a healthy weight, which offers protection from at least a dozen cancers.
Of the many human studies investigating tomatoes, lycopene and cancer risk, most are observational studies of populations. Early research linked tomato consumption and blood levels of lycopene to reduced prostate cancer risk, leading to a focus on the role of tomato consumption and this cancer.
When evidence was dominated by case-control studies (comparing the diets of people who already have cancer with people who do not), there were suggestions that tomatoes, and the lycopene they provide, reduced risk of prostate cancer. But support for these associations has become less clear as evidence quality has improved. A stronger type of research looks at data from a group of people over time. The AICR/WCRF Continuous Update Project analysis of these studies, called cohort studies, shows no significant associations with total or advanced prostate cancer, whether based on diet, blood lycopene levels, or tomato consumption.10 Overall, randomized controlled trials also show no significant association.
- It’s possible that further research will identify a range of tomato or lycopene consumption that reduces risk of prostate cancer. But if there is a link, variations in diagnosis and classifications of the disease have made it more difficult for research to identify a relationship. Prostate cancer often takes decades to develop, with some tumor types aggressive and others slow growing and possibly not lethal. PSA (prostate-specific antigen) tests are often used as a measure of prostate cancer risk, but levels may also rise in non-cancerous prostate conditions. Researchers are continuing to look for more specific indicators, including certain forms of PSA, that may provide more accurate information about overall and aggressive prostate tumor risk.
- Impact of tomato consumption may vary depending on type and stage of this cancer, synergy with other foods, and the proportion consumed as processed tomatoes, which raise blood lycopene levels more than the same amount of raw tomatoes.
Research shows higher dietary, supplement or blood levels of beta-carotene unlikely to have any substantial effect on the risk of prostate cancer, according to the AICR/WCRF Third Expert Report.
Some population studies have linked higher blood levels of total carotenoids and of beta-carotene with a lower risk of overall cancer. Blood levels may more accurately reflect the consumption of carotenoid-rich foods than diet questionnaires, and they include differences in how much is absorbed from food. However, it may be that the lower cancer risk is seen because blood levels of these compounds are recognized as signals of greater overall vegetable and fruit consumption.
- Lung cancer: Population studies have linked higher dietary and blood levels of beta-carotene or total carotenoids with a lower risk of lung cancer. Larger studies now show protection less clearly than earlier studies, and the AICR/WCRF Third Expert Report categorizes this link as Limited Suggestive. Additional research is needed.
- Breast cancer: Some population studies also link higher amounts of carotenoids (including beta-carotene and alpha-carotene) in the diet or blood to lower risk of breast cancer, mainly for estrogen receptor-negative (ER-) forms. The AICR/WCRF Third Expert Report categorized this link as Limited Suggestive. It is possible that an effect of carotenoids on ER-positive (ER+) tumors is masked by the hormonal influences that dominate the risk of ER+ breast cancer. Additional research is needed. One large population study also found total vegetables linked to lower risk of ER-negative breast cancer.
You can have “too much of a good thing”, however. Beta-carotene in high-dose supplements increases lung cancer risk when taken by people who smoke or used to smoke tobacco, according to evidence rated convincing in the AICR/WCRF Third Expert Report.
Tips for Selection, Storage and Preparation
- Choose smooth-skinned plump tomatoes that are firm, but not hard.
- When fresh tomatoes are out of season, try canned tomatoes. Many chefs prefer those for flavor in cooking instead of tomatoes grown in hothouses or transported long distances.
- Buy canned whole or diced tomatoes and tomato purée, sauce, juice or soup with no added salt and little or no added sugar.
- Tomatoes lose flavor at cold temperatures, so store ripe tomatoes at room temperature out of the direct sunlight. If you can’t use the fresh tomatoes before they spoil, refrigerate them, but return them to room temperature for serving.
- Store under-ripe tomatoes in a brown paper bag to ripen; add a ripe apple or banana to give off ethylene gas that speeds the ripening process.
- You can freeze tomatoes to use in sauces or other cooked dishes either chopped or whole. The skins will pop right off when thawed.
- Add raw tomatoes to salads, sandwiches and snack plates.
- Enjoy cooked tomatoes on their own by grilling, baking or broiling them and adding cherry tomatoes to kabobs.
- Add puréed or crushed tomatoes to soup, stew, chili, curry, lasagna, enchiladas, Spanish rice and pasta.
- Start with homemade or commercial tomato soup and add leftover vegetables, beans, whole grains and herbs for a one-pot meal.
- World Cancer Research Fund / American Institute for Cancer Research. Continuous Update Project Expert Report 2018. Wholegrains, vegetables and fruit and the risk of cancer. Available at: dietandcancerreport.org.
- Bohn T. Carotenoids, Chronic Disease Prevention and Dietary Recommendations. International Journal for Vitamin and Nutrition Research. 2017;87(3-4):121-130.
- Kaulmann A, Bohn T. Carotenoids, inflammation, and oxidative stress–implications of cellular signaling pathways and relation to chronic disease prevention. Nutr Res. 2014;34(11):907-929.
- Bouayed J, Bohn T. Exogenous antioxidants – Double-edged swords in cellular redox state: Health beneficial effects at physiologic doses versus deleterious effects at high doses. Oxid Med Cell Longev. 2010;3(4):228-237.
- Kelkel M, Schumacher M, Dicato M, Diederich M. Antioxidant and anti-proliferative properties of lycopene. Free Radic Res. 2011.
- Applegate CC, Rowles JL, Erdman JW. Can Lycopene Impact the Androgen Axis in Prostate Cancer?: A Systematic Review of Cell Culture and Animal Studies. Nutrients. 2019;11(3):633.
- Holzapfel NP, Holzapfel BM, Champ S, Feldthusen J, Clements J, Hutmacher DW. The Potential Role of Lycopene for the Prevention and Therapy of Prostate Cancer: From Molecular Mechanisms to Clinical Evidence. Int J Mol Sci. 2013;14(7):14620-14646.
- Engelmann NJ, Clinton SK, Erdman JW, Jr. . Nutritional Aspects of Phytoene and Phytofluene, Carotenoid Precursors to Lycopene Adv Nutr. 2011;2:51-61.
- Applegate C, Rowles J, III, Miller R, et al. Dietary Tomato, but Not Lycopene Supplementation, Impacts Molecular Outcomes of Castration-resistant Prostate Cancer in the TRAMP Model (P05-015-19). Current Developments in Nutrition. 2019;3(Supplement_1).
- Norat T, Vieira AR, Chan D, et al. The Associations Between Food, Nutrition and Physical Activity and the Risk of Prostate Cancer. WCRF/AICR Systematic Literature Review Continuous Update Project Report. London: World Cancer Research Fund / American Institute for Cancer Research;2014.
- World Cancer Research Fund/American Institute of Cancer Research. Continuous Update Project Expert Report 2018. Other dietary exposures and the risk of cancer. Available at dietandcancerreport.com.
- Aune D, Keum N, Giovannucci E, et al. Dietary intake and blood concentrations of antioxidants and the risk of cardiovascular disease, total cancer, and all-cause mortality: a systematic review and dose-response meta-analysis of prospective studies. Am J Clin Nutr. 2018;108(5):1069-1091.
- Farvid MS, Chen WY, Rosner BA, Tamimi RM, Willett WC, Eliassen AH. Fruit and vegetable consumption and breast cancer incidence: Repeated measures over 30 years of follow-up. International Journal of Cancer. 2019;144:1496-1510.
- Moran NE, Mohn ES, Hason N, Erdman JW, Jr, Johnson EJ. Intrinsic and Extrinsic Factors Impacting Absorption, Metabolism, and Health Effects of Dietary Carotenoids. Advances in Nutrition. 2018;9(4):465-492.