People, who regularly take painkillers such as ibuprofen, may be at increased risk of kidney cancer, according to new research. The findings suggest that the more one uses these drugs, called anti-inflammatory drugs, or NSAIDs increased the risk of developing this cancer.

But you can not prove that the use of analgesic causes cancer, since the difference between regular users and nonusers in the study was small. Researchers calculated that if there is a relationship of cause and effect, about 10,000 people would have to take medication regularly for a person to have kidney cancer.

This does not mean that people who need the drugs should not take them, especially because of their potential benefits over other types of cancer.

NSAIDs have been associated with a reduced risk of several cancers, including colorectal, breast and prostate. The most important implication of this study is that it raises the possibility that NSAIDs may increase the risk of certain cancers as well.

In addition, the drugs are associated with an increased risk of bleeding in the stomach.

The researchers examined data from two studies with about 125 000 nurses and other health professionals who completed surveys every two years until two decades. The surveys asked participants how often they took painkillers for arthritis and other diseases, and also tracked down people who have been diagnosed with kidney cancer.

In total, 333 people (about 0.3%) had kidney cancer. People who reported taking Tylenol or aspirin regularly (two or more times per week) were no more likely to be diagnosed with kidney cancer than those who did not take painkillers.

However, participants who were taking NSAIDs, including ibuprofen (marketed as Advil) and naproxen (sold as Aleve), were about 50% more likely to be diagnosed with cancer.

The risk was even greater in people who took NSAIDs regularly for ten years or more.

Until now, researchers can not explain why aspirin does not increase the risk of kidney cancer, but other NSAIDs yes, while the drugs work in similar ways.

It still can not exclude the possibility that another factor is driving the association. But the fact that the researchers saw the connection in two different study populations means that they are more confident that NSAIDs and kidney cancer are actually related.

So far the results should not drive the decision to someone about whether or not to take painkillers. But if the study is confirmed, risks and benefits should be considered in deciding when to give NSAIDs, especially for a long period of time.