A review of research adds to evidence that people who work in sales may have a slightly elevated risk of bladder cancer - particularly women.

Studies have found higher bladder cancer rates among people in various occupations, including hairdressers, textile workers, truck drivers and workers in the rubber, leather and chemical industries. It’s thought that long-term chemical exposures are to blame.

A number of studies over the past 20 years have also found sales workers to be at higher-than-average risk of bladder cancer. But some researchers have regarded these as chance findings, partly because there is no clear biological explanation for such a link.

For their study, Drs. Andrea Mannetje and Neil Pearce of Massey University in New Zealand analyzed 18 previous studies on occupation and bladder cancer risk.

They found that when other factors were considered - including smoking, a major risk for bladder cancer - women in sales occupations had an 18 percent higher risk of developing the disease than those in other jobs.

The studies varied in their findings on men, and there was no clear overall association between sales jobs and bladder cancer. There was, however, some suggestion that men in car sales had an elevated risk, the researchers report in the American Journal of Industrial Medicine.

Still, it’s not yet clear that there is any true cause-and-effect relationship between sales jobs and bladder cancer, Mannetje told Reuters Health.

“This review of the literature only shows that there is a small increase in bladder cancer risk for female sales workers,” she said. The reason, she added, is unknown.

One plausible hypothesis, Mannetje explained, is that sales workers have less time for bathroom breaks and take in less fluid throughout the day - which might affect their cancer risk because the bladder has a longer contact with potentially cancer-promoting substances in the urine.

All of this is speculation, however, according to Mannetje. Neither bathroom habits nor fluid intake have been shown to affect bladder cancer risk - though some animal research suggest they may. Also unclear is whether sales workers do indeed visit the bathroom infrequently or limit their fluid intake compared with people in other jobs.

Regardless of whether there is a real cause-and-effect relationship, Mannetje pointed out, the best way for people to reduce their risk of bladder cancer is to avoid smoking.

SOURCE: American Journal of Industrial Medicine, March 2006.