"We found that tumour incidence was reduced by 17, 39 and 44 per cent in rats fed the human equivalent of one, three or six apples a day, respectively, over 24 weeks," said Rui Hai Liu, associate professor of food science at Cornell University, and lead author of the study.
The Cornell researchers treated a group of rats with a known mammary carcinogen and then fed them either whole apple extracts or control extracts.
They found that the number of tumours was reduced by 25, 25 and 61 per cent in rats fed, respectively, the equivalent of one, three or six apples a day.
The report, published in the online edition of the Journal of Agricultural and Food Chemistry, concludes that "consumption of apples may be an effective strategy for cancer protection".
Breast cancer is the most common cancer among women across the European Union. Britain has one of the highest breast cancer death rates in the world, according to Breast Cancer Research, with one woman in nine developing the disease during her lifetime.
Liu and his colleagues reported in Nature five years ago that the antioxidants in fresh apples could inhibit human liver and colon cancer cell growth. Antioxidants are thought to help prevent cancer by mopping up free radicals and inhibiting the production of reactive substances that could damage normal cells.
However there has been some debate over the power of fruit and vegetable consumption to fight off breast cancer. Recently reported results from the European Prospective Investigation Into Cancer and Nutrition (EPIC) study, the largest trial ever designed to investigate the relationship between diet and cancer, found no evidence to support the protective effect of fruit and vegetable consumption against breast cancer.
Liu says that increasingly evidence suggestst that "it is the additive and synergistic effects of the phytochemicals present in fruits and vegetables that are responsible for their potent antioxidant and anticancer activities."
Phytochemicals, including phenolics and flavonoids, are thought to be the compounds contributing to the health benefits of apples.
In December a Cornell team demonstrated that quercetin, found in considerable quantities in apples, protects against oxidative damage in rat brain cells, a process responsible for diseases like Alzheimer's.