prevent some cancers by inhibiting the formation of mutagenic n-nitroso compounds (nitrosamine). flavonoids, such as egcg in green tea, have also been shown to be effective antioxidants and may have anti-cancer properties. epidemiological studies indicate that a diet rich in fruits and vegetables is associated with lower incidence of some cancers and longer life expectancy, however, the effectiveness of antioxidant supplements in cancer prevention in general is still the subject of some debate. other chemicals may reduce mutagenesis or prevent cancer via other mechanisms, although for some the precise mechanism for their protective property may not be certain. selenium, which is present as a micronutrient in vegetables, is a component of important antioxidant enzymes such as gluthathione peroxidase. many phytonutrients may counter the effect of mutagens; for example, sulforaphane in vegetables such as broccoli has been shown to be protective against prostate cancer. others that may be effective against cancer include indole-3-carbinol from cruciferous vegetables and resveratrol from red wine. an effective precautionary measure an individual can undertake to protect themselves is by limiting exposure to mutagens such as uv radiations and tobacco smoke. in australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years. in 1981, human epidemiological analysis by richard doll and richard peto indicated that smoking caused 30% of cancers in the us. diet is also thought to cause a significant number of cancer, and it has been estimated that around 32% of cancer deaths may be avoidable by modification to the diet. mutagens identified in food include mycotoxins from food contaminated with fungal growths, such as aflatoxins which may be present in contaminated peanuts and corn; heterocyclic amines generated in meat when cooked at high temperature; pahs in charred meat and smoked fish, as well as in oils, fats, bread, and cereal; and nitrosamines generated from nitrites used as food preservatives in cured meat such as bacon (ascobate, which is added to cured meat, however, reduces nitrosamine formation). overly-browned starchy food such as bread, biscuits and potatoes can generate acrylamide, a chemical shown to cause cancer in animal studies. excessive alcohol consumption has also been linked to cancer; the possible mechanisms for its carcinogenicity include formation of the possible mutagen acetaldehyde, and the induction of the cytochrome p450 system which is known to produce mutagenic compounds from promutagens. for certain mutagens, such as dangerous chemicals and radioactive materials, as well as infectious agents known to cause cancer, government legislations and regulatory bodies are necessary for their control. test systems many different systems for detecting mutagen have been developed. animal systems may more accurately reflect the metabolism of human, however, they are expensive and time-consuming (may take around three years to complete), they are therefore not used as a first screen for mutagenicity or carcinogenicity. bacterial main article: ames test ames test – this is the most commonly used test, and salmonella typhimurium strains deficient in histidine biosynthesis are used in this test. the test checks for mutants that can revert to wild-type. it is an easy, inexpensive and convenient initial screen for mutagens. resistance to 8-azaguanine in s. typhimurium – similar to ames test, but instead of reverse mutation, it checks for forward mutation that confer resistance to 8-azaguanine in a histidine revertant strain. escherichia coli systems – both forward and reverse mutation detection system have been modified for use in e. coli. tryptophan-deficient mutant is used for the reverse mutation, while galactose utility or resistance to 5-methyltryptophan may be used for forward mutation. dna repair – e. coli and bacillus subtilis strains deficient in dna repair may be used to detect mutagens by their effect on the growth of these cells through dna damage. yeast systems similar to ames test have been developed in yeast. saccharomyces cerevisiae is generally used. these systems can check for forward and reverse mutations, as well as recombinant events. drosophila sex-linked recessive lethal test – males from a strain with yellow bodies are used in this test. the gene for the yellow body lies on the x-chromosome. the fruit flies are fed on a diet of test chemical, and progenies are separated by sex. the surviving males are crossed with the females of the same generation, and if no males with yellow bodies are detected in the second generation, it would indicate a lethal mutation on the x-chromosome has occurred. plant assays plants such as zea mays, arabidopsis thaliana and tradescantia have been used in various test assays for mutagenecity of chemicals. cell culture assay mammalian cell lines such as chinese hamster v79 cells, chinese hamster ovary (cho) cells or mouse lymphoma cells may be used to test for mutagenesis. such systems include the hprt assay for resistance to 8-azaguanine or 6-thioguanine, and ouabain-resistance (oua) assay. rat primary hepatocytes may also be used to measure dna repair following dna damage. mutagens may stimulate unscheduled dna synthesis that results in more stained nuclear material in cells following exposure to mutagens. chromosome check systems these systems check for large scale changes to the chromosomes and may be used with cell culture or in animal test. the chromosomes are stained and observed for any changes. sister chromatid exchange is a symmetrical exchange of chromosome material between sister chromatids and may be correlated to the mutagenic or carcinogenic potential of a chemical. in micronucleus test, cells are examined for micronuclei, which are fragments or chromosomes left behind at anaphase, and is therefore a test for clastogenic agents that cause chromosome breakages. other tests may check for various chromosomal aberrations such as chromatid and chromosomal gaps and deletions, translocations, and ploidy. animal test systems rodents are usually used in animal test. the chemicals under test are usually administered in the food and in the drinking water, but sometimes by dermal application, by gavage, or by inhalation, and carried out over the major part of the life span for rodents. in tests that check for carcinogens, maximum tolerated dosage is first determined, then a range of doses are given to around 50 animals throughout the notional lifespan of the animal of two years. after death the animals are examined for sign of tumours. differences in metabolism between rat and human however means that human may not respond in exactly the same way to mutagen, and dosages that produce tumours on the animal test may also be unreasonably high for a human, i.e. the equivalent amount required to produce tumours in human may far exceed what a person might encounter in real life. mice with recessive mutations for a visible phenotype may also be used to check for mutagens. females with recessive mutation crossed with wild-type males would yield the same phenotype as the wild-type, and any observable change to the phenotype would indicate that a mutation induced by the mutagen has occurred. mice may also be used for dominant lethal assays where early embryonic deaths are monitored. male mice are treated with chemicals under test, mated with females, and the females are then sacrificed before parturition and early fetal deaths are counted in the uterine horns. transgenic mouse assay using a mouse strain infected with a viral shuttle vector is another method for testing mutagens. animals are first treated with suspected mutagen, the mouse dna is then isolated and the phage segment recovered and used to infect e. coli. using similar method as the blue-white screen, the plaque formed with dna containing mutation are white, while those without are blue. in anti-cancer therapy many mutagens are highly toxic to proliferating cells, and they are often used to destroy cancer cells. alkylating agents such as cyclophosphamide and cisplatin, as well as intercalating agent such as daunorubicin and doxorubicin may be used in chemotherapy. however, due to their effect on other cells which are also rapidly dividing, they may have side effects such as hair loss and nausea. research on better targeted therapies may reduce such side-effects. ionizing radiations are used in radiation therapy. in fiction in science fiction, mutagens are often represented as substances that are capable of completely changing the form of the recipient or granting them superpowers. powerful radiations are the agents of mutation for the superheroes in marvel comics's fantastic four, daredevil, and hulk, while in the teenage mutant ninja turtles franchise the mutagen is a chemical agent also called "ooze", and for inhumans the mutagen is the terrigen mist. mutagens are also featured in video games such as cyberia, system shock, the witcher, metroid prime: trilogy, resistance: fall of man, resident evil, infamous, freedom force, command & conquer, gears of war 3, starcraft, bioshock, fallout, underrail, and maneater. in the "nuclear monster" films of the 1950s, nuclear radiation mutates humans and common insects often to enormous size and aggression; these films include godzilla, them!, attack of the 50 foot woman, tarantula!, and the amazing colossal man.