Cruciferous Vegetables, Isothiocyanates and Indoles

Cruciferous vegetables, including cabbage, broccoli and cauliflower, constitute between 5 per cent and 25 per cent of all vegetable intake.

Adults in China may eat more than 100 g/day, while the lowest consumption (15 g/day or less) has been reported for people in southern Europe and South Africa.

Eating cruciferous vegetables is associated with reduced risk of cancer, particularly cancers of the stomach and lung.

The observed effect is of the same order of magnitude as that observed for total vegetables.

There is evidence that cruciferous vegetables at levels relevant to human intake or more can inhibit neoplastic and preneoplastic responses in experimental animals, mainly when given simultaneously with carcinogens or throughout the experiment.

Isothiocyanites and indoles are both derived from degradation of glucosinolates, the characteristic sulfur-containing glycosides found in cruciferous vegetables.

In most experimental cancer models, isothiocyanates or indoles show a cancer-preventive effect, the extent depending on the compound, the experimental conditions and the animal species. The evidence is particularly strong for intake of phenylethyl-, benzyl- or 3-phenylpropylisothiocyanate and intake of indole-3-carbinol or diindolylmethane.

Nevertheless, some studies show no cancer-preventive effect and some show effects that could be interpreted as adverse.

Whole cruciferous vegetables, isothiocyanates and indoles have been shown to modulate the activity of biotransformation enzymes and the formation of DNA adducts, intermediate markers of cancer-preventive effects.

Inhibition of cell proliferation and induction of apoptosis may also provide a mechanism for tumour suppression.

The findings of this Handbook should encourage the promotion of cruciferous vegetable consumption as a part of a diet containing a variety of fruit and vegetables to reduce cancer risk and improve health.