The findings, based on an analysis of 13 previous studies, suggest that coffee and tea may be protective against kidney cancer, while milk, soda and juice seem to have no effect one way or the other.
Across the studies, people who drank three or more cups of coffee a day were 16 percent less likely to develop kidney cancer than those who averaged less than a cup per day. And those who sipped just one cup of tea each day had a 15 percent lower risk of the disease than non-drinkers.
The findings appear in the International Journal of Cancer.
Heightened sensitivity to insulin
While the study cannot show that coffee or tea directly lower kidney cancer risk, there are reasons why the beverages could be beneficial, according to the researchers, led by Dr Jung Eun Lee of Harvard Medical School in Boston.
For example, they explain, coffee and tea may increase the body's sensitivity to the blood-sugar-regulating hormone insulin, and researchers suspect that insulin levels over time may affect kidney cancer risk.
Coffee and tea also contain antioxidant compounds that may help protect cells in the kidney from cancer-promoting damage, the researchers point out.
For their study, the investigators combined the results of 13 long-term studies that included a total of 530,469 women and 244,483 men. Each study collected information on participants' diets at the outset and then followed them for seven to 20 years.
Coffee and tea consumption were linked to a lower risk of kidney cancer even when the researchers accounted for a number of factors known to affect people's risk of the disease - such as obesity, smoking and high blood pressure.
"Our results suggest that coffee and tea consumption may be associated with a modestly lower risk of (kidney) cancer, whereas intakes of milk, juice and soda were not associated with risk," Lee's team writes.
They say more studies are needed to understand why coffee and tea might be protective against the disease. - (Reuters Health)
SOURCE: International Journal of Cancer, November 15, 2007.