Arsenic in Drinking Water Ups Risk of Heart Disease

May 19, 2011

May 5, 2011 (New York, New York) — Exposure to even moderate amounts of arsenic in drinking water increases the risk of heart disease, new research from Bangladesh shows, and this risk is further exacerbated in anyone who has ever smoked [1].

This is one of the first studies to quantify the risks of moderate exposure to arsenic in terms of cardiovascular disease and also the first time that a synergistic effect of smoking and arsenic exposure on CVD has been demonstrated, lead author of the new prospective cohort study, Dr Yu Chen (New York University School of Medicine, NY), told heartwire.

She explained that arsenic is a natural element that can enter drinking water supplies in areas where water is primarily sourced from groundwater, and previous studies have shown that high levels of arsenic (>500 µg/L) are associated with an increased risk of many cardiovascular diseases, including hypertension and ischemic heart disease, as well as cancer. "But it is not well established whether there is an association between low (<100 µg/L) or moderate levels (<300 µg/L) of arsenic exposure and cardiovascular mortality and subtypes of mortality, so we aimed to investigate this, and we also wanted to see whether the risks due to arsenic exposure were higher among smokers than nonsmokers," she commented. Chen and colleagues report their findings online May 5, 2011 in BMJ

In an editorial accompanying the study [2], Dr Allan H Smith (University of California, Berkeley) and Dr Craig M Steinmaus (California Office of Environmental Health Hazard Assessment, Oakland, CA) say, "Water contaminated with arsenic is tasteless [and] looks crystal clear, and boiling the water only concentrates the arsenic in it. Chen and colleagues' study adds important new evidence that arsenic increases mortality from ischemic heart disease. . . . They report a clear dose-response trend for mortality.

"In all parts of the world where groundwater is used for drinking, clinicians should ask their patients where they obtain their drinking water. If it comes from a well, the next question should be whether the water has been tested for arsenic. If not, the patient should be urged to have it tested," say the editorialists.

Association Strongest for Heart Disease, Not Obvious for Stroke

Chen told heartwire that arsenic exposure has been a specific problem in past times in countries such as Chile and Taiwan and in areas with private wells in the US. But it can affect anyone who uses wells for drinking water if the soil happens to have high concentrations of this natural element, and the list of affected countries continues to grow. In more developed countries, testing is carried out, she notes, but in some poorer countries, this is not always the case; contamination of groundwater in Bangladesh has been recognized as a massive public-health hazard there.

Chen and colleagues' study is an ongoing prospective cohort study in Araihazar, Bangladesh, an area of 25 km2, where water samples and their geographical coordinates for 5966 neighboring wells were collected before participants were recruited. Between October 2000 and May 2002, they enrolled 11 746 men and women, married and aged between 18 and 75, living in the study area for at least five years, and a primary user of one of these 5966 wells, designated as the "index" well, for at least three years.

The cohort is being actively followed with a personal visit at two-year intervals, including a physical exam and a structured interview conducted by a trained physician, and the present study includes data from the first follow-up (2002 to 2004) and second and third follow-up (2007 to 2009) interviews. The study is also the first to look at arsenic concentrations in the urine, as well as water, to confirm exposure, the researchers note.

The association is stronger for heart disease and is not obvious for stroke.

The arsenic concentrations the participants were exposed to ranged from 0.1 µg/L to 864 µg/L, with a mean of 99 µg/L, offering a "unique opportunity to evaluate the cardiovascular effects of exposure at low to moderate concentrations," they say. Chen notes that the WHO and most Western countries have a "standard" maximally recommended concentration of arsenic in drinking water of 10 µg/L.

"We found a dose-response relationship between arsenic concentrations and CVD mortality, but specifically the association is stronger for heart disease and is not obvious for stroke," Chen told heartwire .

Hazard Ratios for Ischemic Heart Disease in Increasing Quarters of Arsenic Concentration in Water (After Adjustment for Potential Confounders)

Arsenic concentration, µg/L Hazard ratio
<12 1.00 (reference)
12.1–62.0 1.22
62.1–148.0 1.35
148.1–864.0 1.92

p=0.0019 for trend

The researchers found similar associations with urine arsenic concentrations.

Ever-smokers were at an almost threefold higher risk of heart disease associated with arsenic exposure and for those "having both exposures, the risk was greater than the sum of the individual effects," Chen said. "So smokers may experience higher risk of heart disease due to arsenic if they are exposed to arsenic." The hazard ratio for ever-smokers exposed to moderate levels of arsenic was 2.7 compared with nonsmokers not exposed to arsenic.

A synergistic effect of smoking and arsenic exposure on risk of cancer has previously been demonstrated, Chen noted.

Exposure to Groundwater Containing Arsenic Is Widespread

In their editorial, Smith and Steinmaus say that although the relative risk estimates reported here "are moderate compared with those associated with outcomes such as bladder and lung cancer, which often exceed 5, cardiovascular disease is the most common cause of death worldwide, so moderately increased relative risks mean very large numbers of excess cases."

More extensive well testing should be done so that people can know which wells are safe and which are not.

Also, prior research has shown that exposure to arsenic in utero and in children has a major effect on mortality in young adulthood, they note, adding that "more research is needed on the impact of early life exposure and on the mechanisms that make arsenic so toxic."

"In the meantime, there is enough evidence to highlight a serious public-health concern, because exposure to groundwater containing arsenic is widespread through the world. And arsenic poses far higher health risks than any other known environmental exposure, with about one in 10 people dying because of high concentrations of arsenic in water," they observe.

Chen told heartwire that although "people in developing countries understand more and more about arsenic exposure," it is still sometimes difficult to persuade people to walk further for their water. "More extensive well testing should be done so that people can know which wells are safe and which are not," she noted. In the study area that she and her colleagues are assessing, any wells with water containing 50 µg/L or more of arsenic have been now marked out by red signs to discourage their use, she noted.

The authors and editorialists report no conflicts of interest.