Exposure to heavy metals has been linked to cancer, neurological harms, and reproductive or developmental issues. Now, a new study is adding to emerging research showing that exposure to metals such as cadmium, uranium and copper may also be associated with the leading cause of death worldwide — cardiovascular disease.
Metal exposure — that can result from sources such as cigarette smoking, drinking water, pollution, and some foods or consumer products — is associated with accumulation of calcium in the coronary arteries, according to the study published Wednesday in the Journal of the American College of Cardiology.
“The magnitudes of these associations are striking, as they are comparable to those observed for classical … risk factors” such as smoking and diabetes, wrote cardiologists Drs. Sadeer Al-Kindi and Khurram Nasir of Houston Methodist and Dr. Sanjay Rajagopalan of University Hospitals Harrington Heart & Vascular Institute in Cleveland in an accompanying editorial comment on the study. The three experts weren’t involved in the research.
Coronary calcium buildup causes atherosclerosis, a chronic and inflammatory cardiovascular disease marked by narrowed arterial walls and thus reduced blood flow. Partial or full blockages of the arteries can lead to conditions such as stroke and coronary heart disease, which can cause arrhythmia, cardiac arrest or heart failure.
“Our findings highlight the importance of considering metal exposure as a significant risk factor for atherosclerosis and cardiovascular disease,” said lead study author Dr. Katlyn E. McGraw, a postdoctoral research scientist in environmental health sciences at Columbia University’s Mailman School of Public Health, in a news release.
Environmental contaminants have been increasingly recognized as risk factors for cardiovascular disease, but the association of metals with coronary artery calcification has been “largely unknown,” the study authors said. They hypothesized that higher urinary levels of nonessential metals — cadmium, tungsten and uranium — and essential metals — cobalt, copper and zinc — that have previously been associated with cardiovascular disease may be linked with calcification.The relationship between heavy metals and heart health
The team analyzed data from 6,418 adults who were between ages 45 and 84 and had participated in the Multi-Ethnic Study of Atherosclerosis. Between July 2000 and August 2002, participants provided urine samples, and their arterial calcium was measured then and four more times over a 10-year period. The participants didn’t already have clinical cardiovascular disease and were recruited from Baltimore; Chicago; Los Angeles; New York City; St. Paul, Minnesota; and Winston Salem, North Carolina.
A normal coronary artery calcium score is zero, which means there is no calcification in the arteries, while scores from one to 99 indicate mild proof of coronary artery disease. At the study’s start, the median coronary artery calcium level was 6.3.Compared with participants with the least urinary cadmium, the calcification levels of those with the most urinary cadmium were 51% higher at the beginning of the study and 75% higher over the 10-year period, the authors found.
High urinary tungsten, uranium and cobalt levels were associated with 45%, 39% and 47% higher coronary calcification levels over the follow-up period, respectively. For those with the highest amounts of urinary copper and zinc, calcification levels increased by 33% and 57% over 10 years, respectively.
All these findings remained after the authors considered sociodemographic characteristics, lifestyle aspects and cardiovascular risk factors such as diabetes, high cholesterol, blood pressure and blood pressure medications.
The study may help cardiologists continue to tackle a “new frontier” in assessing and treating patients’ heart health, said cardiologist Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, who wasn’t involved in the research.
“When you go see your doctor, they’re going to check your blood pressure, age, weight, cholesterol (and) diabetes,” Freeman said. “It’s not like your doctor says, ‘Oh, I’m going to measure a copper or a manganese or a cadmium level, right?’ So that may become what we do in the future.”
However, although the study shows association, it doesn’t establish causation, Al-Kindi, Nasir and Rajagopalan wrote in the editorial comment.“The potential mechanisms by which these metals might promote atherosclerosis progression thus remains to be elucidated,” they added. However, the study authors think the presence of heavy metals could drive the hardening of arteries partly via increased inflammation.
The trouble with measuring urinary metal levels
The study has a few other limitations. Urinary metal assessments were conducted largely only at the beginning of the study, which may not fully capture long-term exposure patterns, Al-Kindi, Nasir and Rajagopalan wrote.
However, urinary cadmium is generally a strong measure of long-term exposure with low variability over time, the authors said.
“The study team received a grant to measure urinary metals among all participants at baseline and among 10% of participants at visit 5 in the Multi Ethnic Study of Atherosclerosis,” McGraw said via email. The main findings are based on urine measured only at the beginning, while a secondary analysis on that small subset of participants revealed consistent yet insignificant findings.
“Unfortunately, exposure biomonitoring is expensive and we do not currently have funding to measure exposure biomarkers over the 10-year period,” McGraw added. Testing the urine samples partly required shipping them frozen on dry ice both to a biobank and then to a laboratory at Columbia, as well as types of preparation and measuring on different days for the purpose of precision.“The team has applied for more research funding to be able to measure the metals over the 10-year period,” McGraw added, “but this will take a few years even if the grant application is successful.”
Limiting your exposure to heavy metals
The study supports the need of large-scale public health action, Al-Kindi, Nasir and Rajagopalan said.
That includes lowering “acceptable limits of metals in air and water and improve enforcement of metal pollution reduction, particularly in communities experiencing disproportionate exposures,”they added. “Public health measures that have reduced metal exposure … have been associated with reductions in cardiovascular disease mortality.”
In addition to metal exposure from air and drinking water, widespread cadmium, tungsten, uranium, cobalt, copper and zinc pollution comes from agricultural and industrial uses such as fertilizers, batteries, oil production, mining and nuclear energy production, according to the study.
Knowing these sources, some of which are known determinants of cardiovascular disease, “one of the questions is, is it the metals (possibly causing the problem), or is it the things the metals are found in?” Freeman said. It could be a combination of both, which will be hard to tease out, he added.The most important measures for reducing metal exposure need to come from policymakers, but there are some ways you can try, McGraw said — including quitting smoking or vaping, testing your drinking water, and using water filters if needed.
Living a healthy lifestyle with a nutritious, balanced diet and exercise could help limit your exposure or mitigate the potential effects of metals, experts said.
There has also been mixed research on whether chelation therapy, which removes some metals from the body, is beneficial for heart disease and other cardiovascular issues, Freeman and McGraw said.
If your job exposes you to metals, “the appropriate personal protective equipment is critical,” Freeman said. Such equipment may include masks and specially engineered garments and goggles to protect your skin and eyes.
