Many of the
cancers common in the Western world, including colon, prostate and breast
cancers, are thought to relate to dietary habits. Of the known risk factors, many will act through increasing the probability of mutation. Recognised dietary
mutagens include cooked meat compounds, N-
nitroso compounds and
fungal toxins, while high meat and saturated fat consumption, increasing rates of
obesity, and regular consumption of alcohol and tobacco are all dietary trends that could indirectly enhance the probability of mutation. However, there are significant difficulties in implementing and sustaining major dietary changes necessary to reduce the population's intake of dietary
mutagens. Dietary
antimutagens may provide a means of slowing progression toward
cancer, and be more acceptable to the population. Consideration of genetic mechanisms in
cancer development suggest several distinct targets for intervention. Strategies that reduce
mutagen uptake may be the most simple intervention, and the one least likely to result in undesirable side effects. Certain (but not all) types of dietary fibres appear to reduce mutation through this mechanism, as may certain probiotics and large planar molecules such as
chlorophyllin.
Antioxidants have been suggested to scavenge
free radicals, and prevent their interactions with cellular
DNA. Small molecule dietary
antioxidants include
ascorbic acid,
Vitamin E,
glutathione, various
polyphenols and
carotenoids. We found a statistically significant relationship between
colon cancer incidence and soil
selenium status across different regions of New Zealand. Additionally, a study of middle-aged men suggested that blood
selenium levels lower than 100 ng/ml were inadequate for repair or surveillance of oxidative (and other) DNA damage. We suggest that
selenium will be an important
antimutagen, at least in New Zealand, possibly through
antioxidant effects associated with
selenium's role in
enzymes associated with endogenous repair of DNA damage. Modulation of
xenobiotic metabolizing
enzymes is well recognised as
cancer-protective, and is a property of various
flavonoids and a number of
sulfur-containing compounds. Many fruits and vegetables contain compounds that will protect against mutation and
cancer by several mechanisms. For example, kiwifruit has
antioxidant effects and may also affect
DNA repair enzymes. Dietary
folate may be a key factor in maintenance of methylation status, while enhanced overall levels of
vitamins and minerals may retard the development of
genomic instability. The combination of each of these factors could provide a sustainable intervention that might usefully delay the development of
cancer in New Zealand and other populations. Although there are a range of potentially antimutagenic fruits, vegetables and cereals available to these populations, current intake is generally below the level necessary to protect from dietary or endogenous
mutagens. Dietary supplementation may provide an alternative approach.