Diet may mitigate toxic effects of arsenic

A glass of tap water is served at a restaurant in New York June 10, 2009.

NEW YORK (Reuters Health) - People drinking water naturally contaminated with high levels of arsenic may benefit from eating more radishes, sweet potatoes and other similar plants, a new study finds.

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 after being exposed to high levels of arsenic, 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 told Reuters Health.

Arsenic is an element found naturally in rock, soil, water, the air and the food supply. It is also released into the environment through industrial activities; for instance, arsenic is used as a wood preservative and in some paints, dyes and fertilizers.

High arsenic exposure can lead to cancer, and chronic exposure to even moderately elevated levels has been linked to high blood pressure and type 2 diabetes.

The U.S. Environmental Protection Agency (EPA) has set the maximum allowable level of arsenic in drinking water at 10 parts per billion (or 10 micrograms per liter) and is currently considering lowering that limit. According to the Centers for Disease Control and Prevention, about 80 percent of U.S. drinking-water supplies have an arsenic level below 2 parts per billion (ppb), but two percent exceed 20 ppb.

The current findings, which appear in the American Journal of Epidemiology, focus on residents of a region of Bangladesh known for its extremely high levels of arsenic naturally present in drinking water - in some cases, exceeding 200 parts per billion.

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, 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 6 years, noting who developed skin lesions. More than 800 skin lesions developed over the study period.

These lesions are a pre-cancerous condition, Ahsan said in an interview, in which the skin thickens like a freckle, starting small but often spreading. "We used the skin conditions as a marker of more serious conditions," he explained, since evidence suggests people with more skin problems related to arsenic are more likely to have other, more serious, conditions related to arsenic.

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, among 2,419 people who consumed the greatest amounts of roots and gourds, 156 skin lesions developed, versus 248 lesions seen in 2,420 people who ate the smallest amounts of these plants.

The diet heaviest in roots and gourds appeared to lower the risk of lesions by 30 percent 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, Ahsan noted. Some unknown constituent of these plants may somehow help the body flush out arsenic, he suggested. "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," 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."

SOURCE: link.reuters.com/zug54r American Journal of Epidemiology, online December 22, 2010.