More Proof Arsenic in Drinking Water Increases Risk of Heart Disease
Arsenic, even in moderate levels, in drinking water is associated with an increased risk of heart disease. Smokers are even more affected.
A new study published this week in the British Medical Journal has added more proof of this association between arsenic in drinking water and heart disease.
Arsenic is a natural element of the Earth's crust and high concentrations in groundwater pose a public health threat to millions of people worldwide.
High levels of arsenic exposure from drinking water have already been related to an elevated risk of heart disease. The first evidence of a link between cardiovascular disease and arsenic in drinking water came in 1980 from Antofagasta, Chile, with a report of 17 deaths from myocardial infarction in people under the age of 40. This link has been strengthened by other studies over the years.
The study a team of researchers from USA and Bangladesh, led by Dr Yu Chen from New York University School of Medicine and Dr Habibul Ahsan from the University of Chicago, adds important new evidence that arsenic increases mortality from ischemic heart disease.
The researchers set out to test the association between arsenic exposure and death from cardiovascular disease and to assess whether cigarette smoking influences the association.
The prospective cohort study involved 11,746 men and women living in Araihazar, Bangladesh, where groundwater is contaminated by arsenic. The participants resided in an area where exposure to arsenic concentrations in water from drinking wells measured from 0.1 µg/L to 864 µg/L (mean 99 µg /L) at baseline, considered low to moderate concentrations.
Water samples and their geographical coordinates were collected for 5966 contiguous wells in a well defined area of 25 km2 before the participants were recruited.
At the start of the study in 2000, participants were interviewed and underwent a physical examination. Urine samples were also taken and tested for levels of arsenic. This procedure was repeated at two year intervals for an average of 6.6 years.
After adjusting for factors such as age, gender, smoking status and education level, the authors found a dose-response relation between arsenic exposure and deaths from heart disease at a lower level of arsenic exposure than previously reported.
The death rate for cardiovascular disease was 271 per 100,000 person years among individuals drinking water containing moderate levels of arsenic (12 - 864 parts per billion, or ppb) compared with 214 per 100,000 person years among individuals drinking water containing low levels of arsenic (less than 12ppb).
The researchers estimate that almost 30% of these deaths in the study population can be attributable, in part, to moderate levels of arsenic concentrations in well water (12-864 ppb).
The risk of dying from heart disease associated with arsenic exposure was consistently higher in current and former smokers compared with never smokers, suggesting that the cardiovascular effects of arsenic exposure, even at moderate levels, are further intensified by smoking.
The ways in which arsenic leads to heart disease are not clear, but studies suggest that it can induce atherosclerosis (hardening of the arteries), say the authors. "Exposure to arsenic in drinking water is adversely associated with mortality from heart disease, especially among smokers," they conclude.
Arsenic poses far higher health risks than any other known environmental exposure, say Professors Allan Smith and Craig Steinmaus from the University of California, Berkeley, in an accompanying editorial. Yet water contaminated with arsenic is tasteless, looks crystal clear, and boiling the water only concentrates the arsenic in it.
The researchers suggest that, in all parts of the world where groundwater is used for drinking, clinicians should ask patients about their drinking water and, if it comes from a well, urge them to have it tested for arsenic. "It is too late to identify exposure after diseases caused by arsenic have been diagnosed, because many are fatal," they conclude.
Arsenic exposure from drinking water and mortality from cardiovascular disease in Bangladesh: prospective cohort study; Yu Chen, Joseph H Graziano, Faruque Parvez, Mengling Liu, Vesna Slavkovich, Tara Kalra, Maria Argos, Tariqul Islam, Alauddin Ahmed, Muhammad Rakibuz-Zaman, Rabiul Hasan, Golam Sarwar, Diane Levy, Alexander van Geen, Habibul Ahsan; BMJ 2011;342:doi:10.1136/bmj.d2431 (Published 5 May 2011)
Arsenic in drinking water (editorial); Allan H Smith, Craig M Steinmaus, BMJ 2011; 342:d2248 doi: 10.1136/bmj.d2248 (Published 5 May 2011)