Cancer Chemoprevention and Diet

Much of the increasing burden from cancer is preventable.  Unlike with cardiovascular disease where risk factors such as blood pressure and blood lipid profiles can be monitored and treated, the logical steps to prevent cancer are less clear.  Except for the use of drugs such as tamoxifene for treating precancerous cells in those at high risk, no preventative agent with an established risk to benefit profile for the prevention of cancer exists.  The carcinogenesis process takes over 20 years and the idea behind a chemotherapeutic agent would be to halt the progression of premalignant cells in order to reduce the risk from cancer.  Alas, only healthy diet and lifestyle can be relied upon to do this and which may only have a marginal effect in many cases.

Prostate cancer serves as a good model for studying how dietary and lifestyle factors may influence disease incidence.  A strong disparity exists between Eastern and Western cultures and it has been found that migrants from countries with a low incidence acquire an increased incidence within 20 years of moving to the West.  The evidence for dietary components which are protective against prostate cancer are neatly summarised in an article by Venkateswaran and Klotz (2010), in Nature Reviews Urology, 2010.  Highlighted are the micronutrients EGCG and lycopene from green tea and tomatoes, as well as isothiocyanates from eating cruciferous vegetables which are formed by rearrangement reactions following the hydrolysis of glucosinolates by the action of myrosinase enzymes in the plant tissue or the action of gut microflora.  Different isothiocyanates are formed according to the specific glucosinolate precursor, for example sulforaphane is derived from glucoraphanin and allyl isothiocyanate, which gives mustard its pungent taste, is derived from sinigrin.

The different vegetables have various glucosinolate composition, with brussel sprouts being the king of the Cruciferae.  Absorption of isothiocyanates is believed to be greater following ingestion of raw brassica with active plant myrosinase than after consumption of the cooked plant with denatured myrosinase.  Further information is available here.

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