Among residents of Bangladesh, a region highly contaminated with arsenic, those with diets relatively high in roots and gourds - which also include green papaya and pumpkin - were less likely to develop telltale skin lesions from high levels of arsenic exposure, a sign the chemical was probably causing fewer toxic effects.
"Their risk is different based on their intake of different food items," study author Dr Habibul Ahsan of the University of Chicago said.
The US Environmental Protection Agency (EPA) has set the maximum allowable level of arsenic in drinking water at 10 parts per billion (or 10 mcg/L) and is currently considering lowering that limit.
The current findings, which appeared online in the American Journal of Epidemiology, focus on residents of a region of Bangladesh known for its extremely high levels of arsenic in drinking water - in some cases, exceeding 200 parts per billion.
Nutrients that defend body
Previous research has suggested that certain nutrients, such as selenium, vitamin A, iron, folate and zinc, may help the body defend against arsenic, the authors write.
To investigate whether people who drink from arsenic-contaminated wells can mitigate their risk with diet, Dr Ahsan and his team asked nearly 10,000 residents about their diets, tested the levels of arsenic in their wells, and followed them for approximately six years. More than 800 pre-cancerous skin lesions developed over the study period.
"We used the skin conditions as a marker of more serious conditions," Dr Ahsan said in an interview, since evidence suggests people with more skin problems related to arsenic are more likely to have other, more serious side effects of exposure as well.
Roots and gourds a good diet
They found that people who ate diets relatively high in roots and gourds - as opposed to meats or other kinds of vegetables –were less likely to develop arsenic-related skin lesions.
For example, the 2419 people in the quartile that consumed the greatest amounts of roots and gourds had 156 skin lesions, whereas the 2420 in the lowest quartile of consumption of these plants had 248 lesions.
The diet heaviest in roots and gourds appeared to lower the risk of lesions by 30% overall, and some protective effect was seen even among people who drank water very highly contaminated with arsenic.
It's not yet clear why roots and gourds, specifically, might mitigate arsenic's toxic effects. Dr. Ahsan suggested that some unknown constituent of these plants may somehow help the body flush out the toxin.
"Some combination of nutrients that tend to be in excess in these types of foods, together in concert, are making a difference," he said. "We actually do not know exactly."
Finding ways to mitigate arsenic's toxic impact is "urgently needed," Dr Ahsan added.
Once people have been exposed to arsenic for an extended period, their risk of problems remains high, even after the arsenic is removed. "So even if this population gets arsenic-free water tomorrow, that doesn't mean the problem is solved."
(Reuters Health, Alison McCook, January 2011)