People who work as professional painters have a significantly increased risk of developing bladder cancer, researchers in France suggest.

The meta-analysis, published in the journal Occupational and Environmental Medicine, suggests the risk increases the longer a person works as a professional painter.

The authors analyzed almost 3,000 cases of bladder cancer arising in professional painters that were reported in 41 separate studies.

The researchers at the International Agency for Research on Cancer in Lyon, France, say after taking account of smoking -- smoking is a key risk factor for bladder cancer -- painters were still 30 percent more likely to develop bladder cancer than those in the general population. Related occupations, such as plasterers, glaziers, wallpaper hangers, artists and decorators were classified as "painters" in some studies.

The researchers say it is not known which agents in paint may be linked to the increased cancer risk, but the review is complicated by variability of the work, differing levels of exposure and that paint composition has changed over time.

Painters, who were women, were more likely to develop bladder cancer , but only four studies presented results separately for women, the researchers say.