Published: Sep 23, 2013 | Updated: Sep 24, 2013
By Michael Smith, North American Correspondent, MedPage Today
Full Story: http://www.medpagetoday.com/PublicHealthPolicy/PublicHealth/41805
Chronic exposure to arsenic, even at low levels, is associated with an increased risk of cardiovascular disease and death, researchers reported.
In a prospective cohort study, over almost 20 years of follow-up, low levels of arsenic in drinking water and food were associated with increases in incident cardiovascular disease, coronary heart disease, and stroke, according to Ana Navas-Acien, MD, PhD, of Johns Hopkins Bloomberg School of Public Health, and colleagues.
The same was true for death owing to cardiovascular disease, coronary heart disease, and stroke, Navas-Acien and colleagues reported in Annals of Internal Medicine.
The study is a valuable addition to the scientific understanding of the risks of arsenic, commented Elliott Antman, MD, of Brigham and Women’s Hospital in Boston and also president-elect of the American Heart Association.
But, he cautioned, “it’s very important to realize that the absolute level of risk is still far lower than what has been seen with high blood pressure, diabetes, cigarette smoking, or cholesterol elevation.”
“I would not want folks to say if we simply reduced the arsenic in our drinking water, we’d get rid of coronary heart disease,” he told MedPage Today. “It’s not that simple.”
Exposure to high levels of the element — the equivalent of at least 100 micrograms per liter of water — has long been known to be linked to increased rates of cardiovascular disease and mortality, the researchers noted.
But the effect of long-term exposure to lower levels has not been clear, they added. The current U.S. standard for drinking water is less than 10 micrograms per liter.
Indeed, when low levels of arsenic were reported in rice and in syrups made from the grain, the FDA found it impossible to judge immediately whether to change guidelines for the consumption of the foods.
To help fill the gap, Navas-Acien and colleagues turned to the Strong Heart Study, a population-based prospective study of cardiovascular disease among 3,575 residents in three American Indian communities in rural Arizona, Oklahoma, and the Dakotas.
At the time the study started — participants had baseline examination and interviews in 1989 through 1991 — arsenic levels in public water systems ranged from less than 10 to 61 micrograms per liter in Arizona, from less than 1.0 to 21 in the Dakotas, and were uniformly less than 1.0 in Oklahoma. Levels in many private wells would have been higher, the researchers noted.
One implication of those levels is that exposure to arsenic for participants in Oklahoma was likely from food, rather than water, they noted.
To measure arsenic exposure, the investigators used inorganic and methylated arsenic species in urine samples taken at the baseline examinations. To account for dilution, urine arsenic concentrations were divided by urine creatinine and expressed as micrograms per gram of creatinine.
Follow-up continued through 2008, yielding 45,738 person-years of follow-up. All told, 439 participants died from cardiovascular disease, including 341 coronary heart disease deaths and 54 stroke deaths, while 1,184 participants developed fatal or nonfatal cardiovascular disease, including 846 new cases of coronary heart disease and 264 strokes.
Overall, the baseline median urine arsenic concentration was 9.7 micrograms per gram of creatinine but concentrations varied by region, with medians of 14.2, 5.6, and 10.6, respectively, in Arizona, Oklahoma, and the Dakotas, Navas-Acien and colleagues reported.
The investigators stratified arsenic concentration by quartiles, with the highest greater than 15.7 and the lowest less than 5.8 micrograms per gram of creatinine.
After adjustment for sociodemographics, smoking, body mass index, and lipids, comparing incidence and death in the highest and the lowest quartiles led to:
- Hazard ratios of 1.65 (P<0.001), 1.71 (P<0.001), and 3.03 (P=0.061) for death from cardiovascular disease, coronary heart disease, and stroke mortality, respectively. In all cases, the 95% confidence interval excluded unity.
- Hazard ratios of 1.32 (P=0.002), 1.20 (P=0.006), and 1.47 (P=0.032) for incidence of cardiovascular disease, coronary heart disease, and stroke, respectively. Again, all the 95% confidence intervals excluded unity.
Those hazard ratios were attenuated after adjustment for diabetes, hypertension, and kidney disease, which themselves are probably in the “causal pathway” of cardiovascular disease and mortality, the investigators said.
Navas-Acien and colleagues cautioned that arsenic was measured in a single urine sample at baseline and there was no data on individual levels in drinking water. They also noted that there could be unmeasured variables that might confound the results, over-adjustment for variables that could be in the causal pathway, such as diabetes or hypertension, and exposure and outcome misclassification.
The study had support from the National Heart, Lung, and Blood Institute, the Strong Heart Study, and the National Institute of Environmental Health Sciences.
The authors said they had no conflicts.
Primary source: Annals of Internal Medicine