Environmental Factor, June 2011, National Institute of Environmental Health Sciences
Arsenic and smoking synergistic, Superfund study shows
By Anne Johnson
The study builds on ongoing work by Ahsan and Columbia University SRP grant Principal Investigator Joe Graziano, Ph.D. (see story(http://www.niehs.nih.gov/news/newsletter/2010/july/science-arsenic.cfm)), that includes a 2010 study on all-cause mortality and arsenic exposure. (Photo courtesy of Habibul Ahsan and the Columbia University SRP)
Arsenic exposure and cigarette smoking both pose enormous global health challenges. The two are even more deadly in combination, according to a recent study from the University of Chicago Medical Center, funded in part by an NIEHS Superfund Research Program (SRP) grant(http://tools.niehs.nih.gov/portfolio/index.cfm?action=portfolio.grantdetail&grant_number=P42ES010349). The research findings underscore the urgent public health need to prevent arsenic exposure and reduce smoking rates worldwide.
The study(http://www.ncbi.nlm.nih.gov/pubmed/21546419) , led by Habibul Ahsan, M.D.(http://health.uchicago.edu/People/Habibul-Ahsan) , professor of epidemiology and director of the Center for Cancer Epidemiology and Prevention at the University of Chicago, tracked nearly 12,000 Bangladeshi men and women for more than 6 years. It found that arsenic exposure increases a person's risk of dying from cardiovascular disease, and that the effect is magnified up to sixfold in smokers over non-smokers. The findings appeared online May 6 in the British Medical Journal.
Arsenic, an element found naturally in rocks and soils, is known to be toxic. Its role in causing skin lesions, respiratory disease, and several types of cancer has been extensively studied, but its association with cardiovascular disease has only recently drawn attention from the scientific community. This large prospective cohort study sheds new light on the relationships among arsenic exposure, heart disease, and smoking.
Arsenic increases risk for heart disease
An estimated 57 million people in Bangladesh are chronically exposed to arsenic through contaminated well water. Arsenic also poses a threat in many other areas of the globe, including the United States, where about 13 million people are at risk from elevated levels of arsenic in groundwater. People can be exposed to arsenic through drinking water, food, or air.
The researchers recruited 11,746 Bangladeshis starting in 2000 and tracked each individual's exposure to arsenic, smoking behavior, and other factors for an average of 6.6 years. Study participants received a personal visit every two years, which included a physical examination and a structured interview. The researchers measured arsenic exposure by testing drinking water sources and taking urine samples from study participants. The results were adjusted to take into account potential confounders such as age, sex, and body mass index.
During the study period, a total of 460 study participants died, 198 of them from cardiovascular disease. The researchers attributed nearly 30 percent of the deaths from cardiovascular disease to elevated arsenic levels in drinking water.
Those who drank water with high levels of arsenic - above 148 parts per million (ppm) - were nearly 50 percent more likely to die of cardiovascular disease than those drinking water below 12 ppm. The maximum arsenic concentration considered safe by the World Health Organization is 10 ppm.
The association between arsenic exposure and cardiovascular disease death was strongest at the highest levels of arsenic exposure, but even exposure to moderate levels of arsenic - 12ppm to 148 ppm - significantly increased a person's risk of dying from heart disease. The mechanism through which arsenic contributes to cardiovascular disease is not known.
A dangerous interaction
The researchers also studied how cigarette smoking influences the risk of heart disease in those exposed to arsenic. They found that smoking exacerbates the effects of arsenic exposure - the heart disease risk for those who smoke and are exposed to arsenic was greater than the sum of the two risk factors taken separately.
Non-smokers exposed to high levels of arsenic faced a 50 percent greater chance of dying of heart disease than those exposed to safer levels of arsenic. By comparison, current smokers exposed to high levels of arsenic were 300 percent more likely to die of heart disease than smokers exposed to lower levels of arsenic.
Citation: Chen Y, Graziano JH, Parvez F, Liu M, Slavkovich V, Kalra T, Argos M, Islam T, Ahmed A, Rakibuz-Zaman M, Hasan R, Sarwar G, Levy D, van Geen A, Ahsan H.(http://www.ncbi.nlm.nih.gov/pubmed/21546419) 2011. Arsenic exposure from drinking water and mortality from cardiovascular disease in Bangladesh: prospective cohort study. BMJ 342:d2431.
(Anne Johnson is on the staff of MDB, a contractor for the NIEHS Superfund Research Program and Worker Education Training Program.)
Bolstering the argument for primary preventive efforts
The increased risk associated with smoking and arsenic in combination was also seen in former smokers and among those exposed to only moderate levels of arsenic exposure. The findings suggest that smoking influences arsenic toxicity, making even moderate levels of arsenic exposure particularly dangerous for smokers.
The results offer important insights for public health efforts to combat the health effects of both smoking and arsenic exposure. The synergistic effects of smoking and arsenic exposure mean that each factor is even more dangerous in the presence of the other - but the interaction also means that, where both factors exist, a reduction in one factor can have a greater-than-expected impact on improving health and reducing cardiovascular disease.