Toxic metals linked with heart disease
People with heavy exposure to arsenic, lead, cadmium or copper may be more likely to develop cardiovascular disease, a review suggests.
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 noted 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 4200 had a stroke.
Compared with people with the lowest levels of arsenic exposure, those with the highest exposure were 30% more likely to develop cardiovascular disease.
The highest levels of lead exposure were tied to a 43% higher risk, top levels of cadmium were linked to a 33% higher risk and the greatest level of copper exposure was associated with an 81% higher risk.
"These findings reinforce the fact that environmental exposures are equally important (beyond conventional behavioural 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 UK.
Researchers also looked at mercury but did not find a connection to cardiovascular disease. This did not mean mercury was harmless, Dr Chowdhury said.
"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," he said.
Accumulation of toxic metals in the body could lead to metal poisoning and oxidative stress, said study co-author Sara Shahzad, also of the University of Cambridge.
"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 neutralisation by antioxidants," Ms Shahzad said.
"This can consequently affect the cardiovascular and nervous systems, kidneys, eyes and brain."
Previous research had 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 offered fresh evidence of their potential to also contribute to heart disease, the authors concluded.
The studies in the analysis were not controlled experiments and it was also possible that factors like poverty, food and housing quality could impact both the risk of metal exposure and the risk of cardiovascular disease.
"To minimise the exposure to these toxic metals, the government should enforce legislation to control the industrial effluents and sewage discharge leading to hazardous contamination," Dr Chowdhury said.
"In addition, people should be given awareness about common sources of toxic metals in their food, drink and environment."