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Epidemiologic studies suggest that eating more fruit and vegetables results in lower risk for chronic diseases such as cancer. Especially the risk of squamous cell esophagus cancer has been linked to diets deficient in fruit and vegetables. Previous in vivo studies have shown that feeding of tomato juice, paprika juice, dry beans, garlic and soybeans have reduces carcinogenesis. Typical for strawberries is that the phytochemical ellagic acid is found in the fruit pulp, as opposed to other foods were it is found mainly in seeds. This implies a higher bioavailability of ellagic acid in strawberries.
The purpose of this study was to investigate the effect of strawberries on the tumorigenesis in the rat esophagus induced by the carcinogen N-nitrosomethylbenzylamine. The researchers first tested on rats the effect of deep-frozen strawberries on the development of esophagus cancer. After a period of 30 weeks on the strawberry diet the esophageal tumor multiplicity reduced by up to 56 percent. Then the researchers tried to find the mechanism by which strawberries might influence tumorigenesis. The carcinogen N-nitrosomethylbenzylamine acts by methylating DNA, resulting in the formation of O6-methyl guanine, which is linked to carcinogenic mutation. The found that strawberries reduced O6-methyl guanine in the rat esophagus. The numbers of simple leukoplakic lesions was significantly increased by strawberries, while dysplastic leukoplakia lesions were reduced. This indicates that strawberries reduces the conversion of simple leukoplakia to more dangerous dysplastic lesions.
The researchers also investigated if feeding of strawberries, after the administration of the carcinogen, had any effect on tumorigenesis. Also here they found that feeding rats fed with strawberries had a reduced tumor multiplicity by up to 38 percent.
The inhibitory effect of strawberries on tumorigenesis may be related to ellagic acid but may also be the result of the combined effects of other phytochemicals. It is not yet known whether strawberries acts directly on the carcinogenic action of N-nitrosomethylbenzylamine or on the improved repair of damaged DNA. Ellagic acid, ascorbic acid and calcium are known inhibitory agents in strawberries. More studies are required to identity and quantify other phytochemicals with anti-cancer activity.
Source: Stoner GD, Kresty LA, Carlton PS, Siglin JC and Morse MA. Isothiocyanates and freeze-dried strawberries as inhibitors of esophageal cancer.
. Toxicological Sciences.1999 December;52
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