Drinking water contaminated with arsenic may lead to thickening of the heart's main pumping chamber in young adults, increasing the risk for future heart problems, a study warns.

People are most frequently exposed to arsenic, a toxic metalloid, through drinking water in areas where groundwater is contaminated.

"People drinking water from private wells, which are not regulated, need to be aware that arsenic may increase the risk for cardiovascular disease," said Gernot Pichler from Hospital Hietzing/Heart Center Clinic Floridsdorf in Austria.

"Testing those wells is a critical first step to take action and prevent exposure," said Pichler, lead author of the study published in the journal Circulation: Cardiovascular Imaging.

Several studies have shown that arsenic exposure raises the risk of heart disease and its risk factors, including high blood pressure and diabetes.

This is the first study to review the question in young American Indians in Oklahoma, Arizona and North and South Dakota.

Researchers reviewed data from the Strong Heart Family Study, a study evaluating cardiovascular risk factors among American Indians.

Arsenic exposure was measured in urine samples from 1,337 adults (average age 30.7 years, 61 per cent female) and the size, shape and function of their hearts were assessed using ultrasound (echocardiography).

None of the participants had diabetes or heart disease at the start of the five-year study.

Arsenic exposure was higher than in the general US population, but lower than that found in other studies conducted in Mexico and Bangladesh.

With a two-fold increase in arsenic in the urine, the researchers found 47 per cent greater chance of thickening of the heart's main pumping chamber (left ventricle) in the group as a whole.

They also found 58 per cent greater chance of thickening of the left ventricle in participants with increased or high blood pressure.

"The stronger association in subjects with elevated blood pressure suggests that individuals with pre-clinical heart disease might be more prone to the toxic effects of arsenic on the heart," Pichler said.

The study is limited by having only one measure of arsenic exposure, and by the lack of long-term follow-up of the participants.

Although the study was performed in tribal populations in the north, central and southwestern US, the results are likely to be generalisable to millions of people in other rural locations exposed to low or moderate levels of arsenic in their water, said Pichler.

"The study raises the question of whether the changes in heart structure are reversible if exposure is reduced.

"Some changes have occurred in water sources in the study communities, and it will be important to check the potential health impact of reducing arsenic exposure," Pichler said.