Eating citrus daily was associated with a 11 and 14 percent reduction in the incidence of all types of cancer for men and women, respectively, according to a study with 42,270 people living in North Eastern Japan.
Findings published in the International Journal of Cancer also indicate that co-consumption with one cup of green tea a day produced an enhanced protective effect.
“Because of the popularity of citrus and green tea among the Japanese people, these findings suggest that a possible joint effect between them may have implications for public health,” wrote the researchers, led by Wen-Qing Li from Tohoku University Graduate School of Medicine.
“However, we have no information on the difference between a second cup made from the same or another set of leaves, the same as most epidemiological surveys in Japan. In any event, the mechanism responsible for this joint effect needs to be clarified further.”
“Cancer represents a crisis for public health, with a global estimated 12.4 million incident cases and 7.6 million deaths from cancer overall in 2008,” state the Japanese researchers. Some “basic studies” have indicated the potential for citrus to reduce the risk of cancer, linked to the compounds in the fruit exhibiting antioxidant potential.
Despite such links, actual studies of citrus intakes and the incidence of cancer are not abundant.
The Japanese scientists analysed data from 42,470 people in the Ohsaki National Health Insurance Cohort and correlated the effect of citrus and green tea consumption on the overall incidence of cancer. The average age of participants was 59.
After nine years of follow-up, the researchers documented 3,398 cases of cancer. Citrus consumption was divided into five groups: ‘never’; ‘occasionally’; ‘1 to 2 times per week’; ‘3 to 4 times per week’; and ‘daily’.
The results showed that daily consumption was correlated with significant reductions in the risk of all cancer, and especially for prostate and pancreatic cancer. In these cases, the risk reduction was calculated to be 37 and 38 percent, respectively, for daily citrus intakes.
Furthermore, people who drank one cup of green tea a day the reduction in the risk of overall cancer was 17 percent, said the researchers.
“These findings suggest that citrus consumption is associated with reduced all-cancer incidence, especially for subjects having simultaneously high green tea consumption,” wrote the scientists. “Further work on the specific citrus constituents is warranted, and clinical trials are ultimately necessary to confirm the protective effect.”
Commenting on the biological plausibility of the links, the researchers note that data from lab studies have indicated that compounds within citrus fruit, like lycopene, lutein, hesperidin, nobiletin, auraptene, and lime flavonoids and limonoids have shown potential to protect against both prostate and pancreatic cancer.
“Further work on the contributing constituents of citrus is warranted, and clinical trials are ultimately necessary to confirm the protective effect of citrus consumption against cancer,” concluded Li and co-workers.