And the risk increases the longer a person works as a professional painter, the analysis shows.

The authors base their findings on almost 3000 cases of bladder cancer arising in professional painters, reported in 41 separate studies.

Other related occupations, such as plasterers, glaziers, wallpaper hangers, artists and decorators were classified as "painters" in some studies.

The International Agency for Research on Cancer (IARC) estimates that bladder cancer is the 9th most common cancer worldwide, with more than 330,000 new cases diagnosed every year and an annual death toll of 130,000.

A key risk factor for the disease is smoking, but higher numbers than expected of bladder cancer have also been reported for certain types of employment, including painting.

Painters are exposed to some of the same chemicals that are found in cigarette smoke, including aromatic amines.

The authors included studies which assessed whether participants were smokers, in a bid to unpick the impact of painters' occupational exposures on bladder cancer risk.

They found that after taking account of smoking, painters were still 30% more likely to develop bladder cancer than the general population.

This heightened risk persisted when other risk factors were accounted for as well, suggesting that painting is an independent risk factor for the disease.

There was some evidence that female painters were more likely than their male counterparts to develop bladder cancer, but only four studies presented results separately for women.

The researchers say their results are strengthened by the finding that length of employment as a painter had a significant impact on bladder cancer risk.

Those who had worked in this capacity for more than 10 years were more likely to develop bladder cancer than those who had been in this kind of employment for under 10 years.

It is not known which agents are implicated in this heightened risk, say the authors. And the picture is complicated by the variability of the work involved, differing levels of exposure, and the fact that paint composition has changed over time.

But there is now sufficient evidence that painters run an occupational risk of bladder cancer, they conclude. "Because several million people are employed as painters worldwide, even a modest increase in the relative risk is remarkable," they warn.

Note: If no author is given, the source is cited instead.

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