Apr 6, 2016

Phytochemicals for protecting against cancer: evidence from clinical studies

Evidence for a benefit before cancer

Although not all, many studies have linked a higher intake of phytochemical-rich foods, such as vegetables, fruit, legumes, nuts, herbs and spices, with a lower incidence of cancer as highlighted in the latest comprehensive review from the World Cancer Research Fund and other systemic reviews1,2.

More specifically, certain elements of food have been addressed within a number of cohort studies:

  • Carotenoids, found in leafy green vegetables and carrots, have been linked broccoli
    with a lower risk of breast cancer in a recent meta-analysis3 and a lower risk of ovarian cancer4,5,6.
  • Higher intake of cruciferous vegetables, such as cabbage, cauliflower, Brussels sprouts, radishes and broccoli, have been associated with a lower prostate cancer risk7, as have foods rich in isoflavones, such as pulses and soy products8, and lycopene-rich colourful fruits and tomatoes9.
  • Foods with abundant levels of flavonoids, such as onions, rich in quercetin, have been shown to reduce the incidence of numerous cancers, particularly those arising from the lung among smokers10, 11.
  • The anthoxanthins in dark chocolate have been reported to lower the risk of colon cancer12 and higher green tea intake lowers the risk of breast, prostate, ovarian and oesophageal cancers, particularly among smokers and alcoholics13,14.
  • Coffee consumption has been shown to reduce the risk of non-melanomatous skin cancers and melanoma, even after removing other factors such as ultraviolet radiation exposure, body mass index, age, sex, physical activity, alcohol intake and smoking history15,16.

Evidence for a benefit after cancer

The benefits of healthy foods do not stop after a diagnosis, especially if combined with other healthy lifestyle habits:

  • Breast cancer survivors who regularly consumed more than thevegetables government-recommended five portions of fruit and vegetables a day had a third lower breast cancer recurrence risk if combined with regular physical activity17.
  • In another study, women with breast cancer who had the highest serum lignan levels, reflecting good intake of legumes, cereals, cruciferous vegetables and soya, were reported to have the lowest risk of death18. Likewise, a lignin- and polyphenol-rich diet was associated with a lower colorectal cancer relapse rate19.
  • The large Shanghai Breast Cancer Survival Study demonstrated that women with the highest intake of the phytoestrogenic polyphenols isoflavones and flavanone, found in soya and other beans, had a 29% lower risk of relapse and death20. Similar findings were seen for green tea after breast21 and colorectal cancer19. Green tea also decreased the abnormal white cell count in 30% of patients with chronic leukaemia and reduced the levels of several markers of proliferation, as well as serum prostate-specific antigen (PSA) in men with prostate cancer22. A slowing of PSA progression has similarly been observed in other dietary studies, most notably in the randomised trial involving a plant-based diet together with other lifestyle changes23 and a phase II study of pomegranate juice24.
  • Another cancer influenced by nutrition is skin cancer, as highlighted by a study of individuals who have been treated for basal cell carcinoma or squamous cell carcinoma, and who have a high risk of further lesions due to their on-going solar damage. Those who consumed the highest levels of lutein- and zeaxanthin-rich foods, such as leafy green vegetables, had the lowest levels of new cancer formation25.
  • A number of other studies evaluating the impact of phytochemicals are underway, the largest and probably most comprehensive is the UK’s DietCompLyf prospective trial involving 3,159 women treated for breast cancer26.

Sources:

  1. Key TJ. Fruit and vegetables and cancer risk. British Journal of Cancer 2011;104: 6–11.
  2. Block G, Patterson B and Subar A. Fruit, vegetables and cancer prevention: a review of the epidemiological evidence. Nutrition and Cancer 1992;18(1): 1–29.
  3. Hu F, Wang YB, Liang J, et al. Carotenoids and breast Cancer risk: a meta-analysis and meta-regression. Breast Cancer Research and Treatment 2012;131(1): 239-253.
  4. Tung K, Wilkens LR, Wu AH, et al. Association of dietary vitamin A, carotenoids and other antioxidants with the risk of ovarian cancer. Cancer Epidemiology, Biomarkers & Prevention 2005;14: 669.
  5. Banim PJ, Luben R, McTaggart A, et al. Dietary antioxidants and the aetiology of pancreatic cancer: a cohort study using data from food diaries and biomarkers. Gut 2012;62(10): 1489-1496.
  6. Chaoyang L, Ford ES, Zhao G, et al. Serum alpha-carotene concentrations and the risk of death amongst US adults. Archives of Internal Medicine 2011;171(6): 507-515.
  7. Joseph MA, Moysich KB, Freudenheim JL, et al. Cruciferous vegetables, genetic polymorphisms and prostate cancer risk. Nutrition and Cancer 2004;50(2): 206-213.
  8. Song-Yi, Suzanne PM, Lynne RW, et al. Legume and isoflavone intake and prostate cancer risk: The Multi-ethnic Cohort Study. International Journal of Cancer. 2008;123(4): 927-932.
  9. Giovannucci E, Rimm EB, Liu Y, et al. A prospective study of tomato products, lycopene and prostate cancer risk. Journal of the National Cancer Institute 2002;94: 391-398.
  10. Knekt P, Jarvinen R, Seppanen R, et al. (1997) Dietary flavonoids and the risk of lung cancer and other malignant neoplasms. American Journal of Epidemiology 1997;146: 223–230.
  11. Le Marchand L, Murphy SP, Hankin JH, et al. Intake of flavonoids and lung cancer. Journal of the National Cancer Institute 2000;92: 154 –160.
  12. Rodríguez-Ramiro D, Ramos S, López-Oliva E, et al. Cocoa-rich diet prevents azoxymethane-induced colonic preneoplastic lesions in rats by restraining oxidative stress and cell proliferation and inducing apoptosis. Molecular Nutrition & Food Research 2011;55: 1895-1899.
  13. Sun CL, Yuan JM, Koh WP, et al. Green tea and cancer risk: The Singapore Chinese Health Study. Carcinogenesis 2007;28(10): 2143-2148.
  14. Wu LL, Chiou CC, Chang PY, et al. Urinary 8-OHdG: a marker of oxidative stress to DNA and a risk factor for cancer, atherosclerosis and diabetics. Clinica Chimica Acta 2004;339(1-20): 1-9.
  15. Song F, Qureshi A and Han J. Increased caffeine intake is associated with reduced risk of basal cell carcinoma of the skin. Cancer Research 2012;72(13): 3282-3289.
  16. Loftfield E, Freedman ND, Graubard BI, et al. Coffee drinking and cutaneous melanoma risk in the NIH-AARP diet and health study. Journal of the National Cancer Institute 2015;107(2): 1-9.
  17. Pierce JP, Natarajan L, Caan BJ, et al. Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: the Women’s Healthy Eating and Living (WHEL) randomized trial. Journal of the American Medical Association 2007;298(3): 289-298.
  18. Buck K, Vrieling A, Zaineddin AK, et al. Serum enterolactone and prognosis of post-menopausal breast cancer. Journal of Clinical Oncology 2011;29(28): 3730-3738.
  19. Zhu Y, Wu H, Wang PP, et al. Dietary patterns and colorectal cancer recurrence and survival: a cohort study. British Medical Journal Open 2013;3(2): e002270.
  20. Boyapati SM, Shu XO and Ruan ZX. Soy food intake and breast cancer survival: a follow up of the Shanghai Breast Cancer Study. Breast Cancer Research and Treatment 2005;92: 11–7.
  21. Ogunleye AA, Xue F and Michels KB. Green tea and breast cancer risk of recurrence: A meta-analysis. Breast Cancer Research and Treatment 2010;119(2): 477.
  22. Shanafelt TD, Call TG, Zent CS, et al. Phase I trial of daily oral polyphenon E (green tea extract) in patients with asymptomatic stage 0-II chronic lymphatic leukaemia. Journal of Clinical Oncology 2009;27(23): 3808–3814.
  23. Ornish D, Weidner G, Fair WR, et al.; Intensive lifestyle changes may affect the progression of prostate cancer. Journal of Urology 2005;174: 1065-1070.
  24. Pantuck AJ, Leppert JT, Zomorodian N, et al. Phase II study of pomegranate juice for men with rising PSA following surgery or radiation for prostate cancer. Journal of Urology 2005;173: 225–226.
  25. Heinen MM, Hughes MC, Ibiebele TI, et al. Intake of antioxidant nutrients and the risk of skin cancer. European Journal of Cancer 2007;43(18): 2707-2716.
  26. Swann R, Perkins KA, Velentzis LS, et al. The DietCompLf study: A prospective cohort study of breast cancer survival and phytoestrogen consumption. Maturitas 2013;75: 232-240.
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