Drinking coffee has a preventive effect on kidney cancer.

An analysis of the results from 13 previous studies showed that coffee and tea were protective against kidney cancer, while milk, soda and juice seemed to have no effect on kidney health.

Previous studies have shown that people who drink three or more cups of coffee a day have a 16% lower risk of kidney cancer than those who drink less than one cup of coffee a day on average, and people who drink only one cup of tea a day have a 15% lower risk of kidney cancer than those who do not drink tea.

The findings were published in the International Journal of Cancer Research.

Although the study cannot directly prove that drinking coffee and tea prevents kidney cancer, there is some scientific evidence, the researchers said. The study was led by Dr. Jeanne Lee of Harvard Medical School in Boston.

Coffee and tea, for example, increase sensitivity to insulin, the blood-sugar-regulating hormone. Insulin levels are a major factor affecting kidney health, researchers say.

In addition, the researchers note that antioxidants in coffee and tea protect kidney cells from damage.

The researchers combined results from 13 long-term studies involving 530469 women and 244483 men. Each study initially collected dietary information from participants and then followed them for seven to 20 years.

The findings were based on a combination of factors that could trigger kidney cancer, such as obesity, smoking and high blood pressure.

"The results suggest that tea and coffee slightly reduce the risk of kidney cancer, while drinks such as milk, juice and soda have no effect," the researchers wrote in the study.