While these elements occur naturally in the earth’s crust, certain metals can also appear at unsafe levels in drinking water, food, and air as a result of agricultural and industrial practices, mining, and smoking, the research team notes in The BMJ. Copper and lead, for example, can seep into drinking water from corroded pipes, while arsenic and cadmium can accumulate in groundwater due to runoff from factories and crop irrigation systems and are also found in cigarette smoke.
For the analysis, researchers examined data from 37 earlier studies with a total of almost 350,000 participants. Overall, about 13,000 people had heart attacks, bypass surgery or other events related to heart disease and about 4,200 had a stroke.
Compared to people with the lowest levels of arsenic exposure, those with the highest exposure were 30 percent more likely to develop cardiovascular disease. The highest levels of lead exposure were tied to a 43 percent higher risk, top levels of cadmium were linked to 33 percent higher risk, and the greatest level of copper exposure was associated with 81 percent higher risk.
“These findings reinforce the fact that environmental exposures are equally important (beyond conventional behavioral risk factors such as physical activity or diet) for cardiovascular risk, and should not be ignored,” said lead author Dr. Rajiv Chowdhury of the University of Cambridge in the United Kingdom.
Researchers also looked at mercury but didn’t find a connection to cardiovascular disease. This doesn’t mean mercury is harmless, Chowdhury said by email.
“Mercury can also be a marker of fish consumption. It is possible that the association between mercury and cardiovascular disease in these studies which we included may have been somewhat confounded by comparative benefits of fish intake,” Chowdhury added.
Accumulation of toxic metals in the body can lead to metal poisoning and what’s known as oxidative stress, said study co-author Sara Shahzad, also of the University of Cambridge.
As the body uses oxygen, it produces by-products called free radicals that can damage cells and tissues. The damage by oxygen free radicals is known as oxidative stress.
“Oxidative stress is essentially an imbalance between the production of free radicals and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants,” Shahzad said by email. “This can consequently affect the cardiovascular and nervous systems, kidneys, eyes, and brain.”
Previous research has linked the metals in the study to an increased risk of cancer, especially at higher exposures over longer periods of time. But by pooling results from several smaller studies, the current analysis offers fresh evidence of their potential to also contribute to heart disease, the authors conclude.
The studies in the analysis were not controlled experiments designed to prove whether or how exposure to metals in the environment might directly cause heart attacks or strokes. It’s also possible that factors like poverty, food and housing quality could impact both the risk of metal exposure and the risk of cardiovascular disease.
There’s not much most people can do to avoid environmental exposure to toxic metals, Chowdhury said. Limiting exposure requires government action to restrict activities that cause pollution and to encourage remediation when metals are released into the environment as a result of agricultural or industrial practices.
“To minimize the exposure to these toxic metals, the government should enforce legislation to control the industrial effluents and sewage discharge leading to hazardous contamination,” Chowdhury said. “In addition, people should be given awareness about common sources of toxic metals in their food, drink, and environment to minimize the exposure.”
By Lisa Rapaport