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Dr. Ana Navas-Acien can’t quite recall the moment when she began to worry about arsenic in drinking water and its potential role in heart disease.

Perhaps it was when she read a study suggesting a link among people in Bangladesh.

And a similar study in Taiwan. And in Chile.

Several years ago, Dr. Navas-Acien, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, decided to see if similar links could be found in the United States.

She found an ideal group — a stable population relying mainly on private well water — in an ongoing study of Native Americans in the Dakotas and the Southwest. Known as the Strong Heart Study, the project had tracked the lifestyles and environmental exposures of more than 4,000 people since the late 1980s.

As it turned out, Native Americans also were worried about arsenic in their well water. Although the Environmental Protection Agency sets a 10 parts-per-billion safety standard for drinking water, only municipal water utilities are required to meet it.

In private wells, arsenic — resulting mostly from geological contamination of ground water — has been measured in much higher levels, in some cases more than one hundred times higher. The problem is particularly acute in the Southwest, the upper Midwest and northern New England.

So Dr. Navas-Acien and her colleagues compared urinary arsenic levels and disease rates among the Native Americans in the study. As levels of arsenic rose in individuals, she found, so did the incidences of atherosclerosis, of stroke, of heart attack. For those with chronic exposure to arsenic, rates of cardiovascular illness were often doubled, even after taking into account various lifestyle and genetic risks.

“On the question of whether arsenic is a cardiovascular risk, I would say yes, and I would put my hand in the fire to that,” Dr. Navas-Acien said.

It’s a position supported by a growing cohort of researchers and clinical cardiologists, who worry that environmental exposures generally are an underestimated risk in heart disease. The most troubling are thought to be air pollution, metallic elements like arsenic, and heavy metals such as cadmium and lead.

“We need more cardiologists to be thinking about environmental effects on the heart,” said Dr. Gervasio Lamas, chief of cardiology at Mount Sinai Medical Center in Miami. “It’s not just some abstract E.P.A. problem. It’s actually affecting our patients.”

The growing interest in metallic compounds has led to a new understanding of how materials do harm on a cellular level. Arsenic may not be a heavy metal, but it shares some similarities, including the ability to cause free radical damage to cells, stressing delicate blood vessels and thickening arterial walls.

“Arsenic can stimulate enzymes to produce hydrogen peroxide,” said Aaron Barchowsky, a professor of environmental and occupational health at the University of Pittsburgh. Hydrogen peroxide can prompt a cascade of inflammatory responses in cells.

Other metals also stimulate hydrogen peroxide production, but Dr. Barchowsky has found that arsenic also binds to certain receptors on fat cells, altering their normal metabolism and disrupting the normal breakdown of fatty materials. This tends to encourage the formation of artery-clogging plaques, scientists say. Arsenic can also scar cells in a way that causes artery walls to thicken, restricting blood flow.

These effects can occur at remarkably low levels of exposure. Yu Chen, an associate professor of epidemiology at New York University, has studied the risks of arsenic at lower ranges of exposure in Bangladesh, a country plagued by naturally occurring arsenic that contaminates ground water.

Dr. Chen and her colleagues found an increase in death from cardiovascular disease in 20,000 residents exposed to levels of arsenic in drinking water in only the 100-parts-per-billion range. Many people in the study were exposed to arsenic for two decades or more. Recent evidence suggests that the earlier the age of exposure, the more profound the effects.

Dr. Chen is now planning to look at whether prenatal exposure to arsenic, via a mother’s drinking-water consumption, can affect blood pressure as early as adolescence.

The physical symptoms of arsenic exposure in her mortality study included an increase in irregular heartbeats and a cell-by-cell thickening of arterial walls.

She and her colleagues also found that arsenic appeared to amplify the damaging effects of smoking: Death rates accelerated sharply among smokers exposed to arsenic. Other studies suggest that arsenic may also contribute to the development of diabetes, which is another factor in cardiovascular disease.

As researchers learn more about such risks to heart health, they are also pursuing solutions from better education to direct intervention.

Dr. Lamas is helping to organize a panel, at the spring meeting of the American Heart Association, that will outline to doctors the dangers of environmental exposure. He has also been exploring the idea that chelation — a treatment that helps removed stored metals from the body — might be useful in some cases.

Dr. Navas-Acien is continuing to work with Native Americans to reduce their exposure to arsenic. She’s planning a new study that will look at whether adding filters to household wells will help bring down cardiovascular disease rates in rural areas.

“We’re increasingly understanding the environmental risks for cardiovascular disease,” she said. “Air pollution, lead, cadmium and arsenic are all proven factors. Which leads to a responsibility to do something about that.”