By Megan Avakian
Researchers funded by NIEHS recently found an association between arsenic in drinking water in northern Chile and hypertension, or high blood pressure, which is a risk factor for cardiovascular disease (CVD). This is the first study to examine arsenic-associated hypertension using individual lifetime exposure data, providing an advantage over past studies, which have mostly relied on measurements taken at a single point in time to estimate exposure.
According to senior study author Craig Steinmaus, M.D., from the University of California, Berkeley, several factors make northern Chile a valuable area for studying the long-term effects of exposure to arsenic in drinking water. “The Atacama Desert in northern Chile is extremely dry, and as a result there are very few water sources, so most people get their water from the public utility in their city. Additionally, these cities have been collecting data on arsenic concentrations in the water for over five decades and there is a wide range of exposure between cities,” said Steinmaus. “So we are able to generate a detailed lifetime exposure history just by knowing what city an individual lived in and what water they were drinking.”
Millions of people around the world are exposed to arsenic concentrations in drinking water above the World Health Organization’s (WHO) recommended limit of 10 µg/L. Arsenic is a known carcinogen and has been associated with CVD, the leading cause of death worldwide. A better understanding of the link between arsenic and CVD risk factors, like hypertension, could shed light how arsenic exposure leads to overt cardiac diseases.
The research team analyzed data collected between October 2007 and December 2010 for a cancer case-control study in the Tarapacá and Antofagasta regions in northern Chile. Data included lifetime individual arsenic exposure estimates and information on potential confounders, such as body mass index, smoking, and diet, for 1,266 participants with and without cancer. During interviews, participants who self-reported either a physician diagnosis of hypertension or use of anti-hypertension medication were classified as having hypertension; the remaining participants were used as controls. The researchers used two exposure metrics to examine the relationship between arsenic and hypertension: cumulative lifetime exposure and highest five-year average exposure.
They found a positive association between arsenic concentrations in drinking water and hypertension for both exposure metrics. Compared to those in the lowest exposure category for highest five-year average exposure (<60 µg/L), participants in the middle (60 - 623 µg/L) and highest (>623 µg/L) exposure categories had 1.49 and 1.65 higher odds of having hypertension, respectively. The researchers found similar results when using the cumulative exposure metric to conduct the analysis.
According to Steinmaus, these findings suggest that hypertension could be one of the mechanisms by which arsenic exposure causes serious cardiac diseases. Additionally, these findings have implications for regulations set to limit arsenic exposure. “Arsenic regulatory standards often only consider the risks related to cancer,” explained Steinmaus. “Including other arsenic-related health risks, like hypertension, into standards could lead to a more protective rule.”
Steinmaus and colleagues are now trying to better understand why some people are more susceptible to arsenic’s toxic effects than others. Using the northern Chile cohort, as well as data from an additional 1,500 participants from two new cohorts in the same area, they will use Superfund Research Program and other NIEHS funding to explore how factors like stress, obesity, low socioeconomic status, and secondary workplace exposures influence an individual’s response to arsenic exposure.
“Typically, regulatory standards are developed for the healthy individual; but if standards are set based on a healthy population we are not protecting the more vulnerable groups,” explained Steinmaus. “We want to understand who is susceptible, what those susceptibility factors are, and how we can better protect those susceptible populations in the future.”
A Focus on Heart Health in February
February marks American Heart Month, providing an opportunity to raise awareness of the global burden of cardiovascular disease (CVD) and how environmental exposures contribute to CVD prevalence. According to the WHO, CVDs are the number one cause of death worldwide. In 2012, CVDs caused an estimated 17.5 million deaths — over three quarters of these deaths were in low- and middle-income countries (LMICs).
Although there are many risk factors for heart disease, such as smoking, unhealthy diet, and obesity, environmental exposures also play a role. NIEHS grantees are investigating how exposures such as arsenic, indoor air pollution, pesticides, lead and more may make an individual more susceptible to cardiovascular problems. A better understanding of how these exposures, which often disproportionally affect populations living in LMICs, are related to CVDs can lead to more effective prevention strategies to protect vulnerable populations.