Increased intake of the antioxidant vitamins C and E could cut the risk of kidney cancer by 28 and 44%, respectively, says a new study from Italy.
More than 80% of all kidney cancers are accounted for by renal cell carcinoma (RCC). Age, sex, obesity, smoking and several genetic and medical conditions are believed to be risk factors, but epidemiological data to support the role of diet in kidney cancer aetiology have yielded mixed results.
“In the present study, based on a large dataset and with extensive information on major sources of vitamins and micronutrients in the Italian population, an inverse relation was observed between vitamin E and vitamin C intake and RCC risk,” wrote lead author Cristina Bosetti from Milan’s Istituto di Ricerche Farmacologiche, “Mario Negri”.
How the study was done
The multi-centre case-control study, published in the International Journal of Cancer, assessed the dietary intakes of 767 renal cell cancer patients (494 men and 273 women) and 1 534 controls (988 men and 546 women) using a 78-item food frequency questionnaire (FFQ) from which micronutrient intakes were calculated.
After adjusting the results to eliminate possible confounding factors, such as age, BMI, sex, smoking habits and alcohol consumption, the researchers calculated that an intake of more than 17,5 micrograms per day of vitamin E was associated with a 44 percent reduced risk of renal cell cancer, compared to those with an intake of, on average, 11,9 micrograms.
They also report an intake of more than 186 micrograms per day of vitamin C was associated with a 44 percent reduced risk of renal cell cancer, compared to those with an intake of, on average, 89,4 micrograms. This result, said the researchers, was of borderline significance.
No statistically significant association was observed for any of the the other micronutrients analysed, including retinol (vitamin A), alpha and beta-carotene, lutein and zeaxanthin, vitamin D, thiamine, folate, and other B vitamins, and lycopene.
“The present findings support a possible beneficial effect of vitamin E and C on RCC,” said the researchers.
Antioxidant activity the cause?
The mechanism behind the potential protective effects was not investigated by the researchers, but they state that the antioxidant activity of the vitamins could explain the benefits. They do state, however, that since the main sources of vitamin E in the Italian diet are olive oil and vegetables, it may reflect a wider effect of these foods.
“Vitamin E may represent an indirect indicator of a diet rich in vegetables, which are usually consumed with olive oil in this population, and have been related to a reduced risk of RCC,” wrote Bosetti.
“Thus, it is possible that, as for other common neoplasms, the favourable effect of plant food may be due to other still unidentified compounds, or to the complex action of several micronutrients combined.”
The study does have several notable limitations, including relying on food frequency questionnaires to gather dietary information. FFQs are susceptible to recall of the subjects. It is also not known if cases adjusted their diet after diagnosis of their disease. - (Decision News Media, January 2007)
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