Cruciferous vegetables such as broccoli, cauliflower, Brussels sprouts, water cress, kale and cabbage contain a class of chemicals called glucosinolates. Glucosinolates are of interest because they are converted in humans to indoles and isothiocyanates, which have been shown to have beneficial effects against certain cancers, such as colon cancer. Cruciferous vegetables are a unique source of glucosinolates and as such much research has been performed on the benefits of increased intakes. High intakes of glucosinolates may not guarantees increased protection from cancer because isothiocyanate metabolism shows genetic differences between individuals. The enzyme glutathione S-transferase (GST) catalyses the conjugation of isothiocyanates with glutathione, increasing their excretion rate from the body and decreasing their ability to induce phase II detoxification enzymes and inhibit cell proliferation. Epidemiological research suggests that GST genotype variations are indeed related to the protection from cancer.
Researchers1 have investigated the association between urinary isothiocyanate excretion and colorectal cancer, as well as the modifying effects of GST genotypes in a prospective study of 322 colon cancer cases and 1251 controls. The results showed that urinary isothiocyanate concentrations were inversely associated with colorectal cancer risk but only in the cases were the subjects had the deletions in the GSTT1 and GSTM1 genes. When the association between urinary isothiocyanates and colorectal cancer was investigated in individuals with intact GSTT1 and GSTM1 genes, there was no statistically significant correlation. Individuals with deletions of one gene but not the other had an intermediate level of isothiocyanate excretion. This data supports previous epidemiological studies that have found associations between isothiocyanate excretion and lung cancer in men with GSTT1 and GSTM1 deletions, and supports the contention that genetic variation alters risks for some types of cancer.
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