NEW YORK (Reuters Health) - Having a drink or two per day appears to modestly decrease the risk of developing kidney cell cancer, new research findings suggest, regardless of the type of alcoholic drink that is consumed.

Multiple studies have hinted at an inverse association between alcohol and kidney cancer, investigators point out in the Journal of the National Cancer Institute. "But previous studies were inconclusive, and it is not clear whether alcohol itself affects risk, or if the effects are due to specific types of beverages," lead author Dr. Jung Eun Lee told Reuters Health.

Eun Lee, from Brigham and Women's Hospital in Boston, and her colleagues therefore analyzed data from 12 clinical studies. "The data were derived from general populations in the United States, Canada, Sweden, Finland and the Netherlands," the investigator said, making their study "one of the largest to examine alcohol intake and risk of kidney cancer."

The total number of subjects included 530,469 women and 229,575 men. At study entry, the subjects had completed food-frequency questionnaires that included alcoholic beverages. The authors defined moderate drinking as the equivalent of "slightly more than one alcoholic drink per day." They excluded subjects who drank more than two drinks per day.

During 7 to 20 years of follow-up, 711 women and 719 men were diagnosed with kidney cell cancer.

This translated into 23 cases for every 100,000 non-drinkers per year and 15 cases for every 100,000 moderate drinkers per year.

After the researchers factored in the effect of age, the risk of kidney cell cancer was 25 percent lower among the moderate drinkers than among the nondrinkers, a statistically significant difference.

There also appeared to be a dose-response relationship - as the amount of daily alcohol consumption increased from about two drinks per week to about one drink per day, the risk of kidney cancer when from 6 percent lower to 25 percent lower, respectively.

The associations were still similar after taking into account risk factors for kidney cancer, including weight, history of high blood pressure, smoking and other factors, the investigators report.

Reproductive history, the use of dietary substances, and total calorie intake, had little impact.

The results were similar for beer, wine, and liquor.

However, the investigators were not able to distinguish between subjects who were moderate daily alcoholic drinkers versus those who tended to drink large amounts sporadically. Therefore the effects of very heavy alcohol use, frequency of use, and various drinking patterns, were unclear, Dr. Eun Lee said.

The investigators suggest that alcohol may reduce the risk of kidney cell cancer by improving insulin sensitivity. Other possibilities include the activity of antioxidant phenolic compounds contained in alcohol, which may help decrease kidney cell cancer risk by removing carcinogenic agents, reducing cancer cell proliferation or promoting cell death.

On the other hand, they add, "Alcohol per se is most likely the responsible factor."

Regardless of the mechanism involved in this moderate reduction in risk, patients should be reminded that alcohol can also increase the risk of many other types of cancer, including breast, liver and esophageal cancer, Eun Lee cautioned.

"Maintaining a healthy weight and avoiding smoking are the principal known means to reduce the risk of (kidney) cancer that should be encouraged, and doing so may also reduce the risk of many other cancers, as well as cardiovascular disease," the research team concludes.