Copper appears to be one of the main environmental factors that cause Alzheimer's disease and contribute to its progression, according to a study of mice and, in some phases, human brain cells.
The common metal prevents the clearance and accelerates the accumulation of toxic proteins in the brain, the researchers said.
"It is clear that, over time, copper's cumulative effect is to impair the systems by which amyloid beta is removed from the brain," study author Rashid Deane, a research professor in the department of neurosurgery at the University of Rochester Medical Center, said.
"This impairment is one of the key factors that cause the protein to accumulate in the brain and form the plaques that are the hallmark of Alzheimer's disease," Deane said.
Where copper is found
People have extensive exposure to copper. The mineral appears in drinking water carried by copper pipes, in nutritional supplements, and in foods such as red meat, shellfish, nuts, and many fruits and vegetables, according to the news release. Copper plays an important and healthy role in nerve conduction, bone growth, the formation of connective tissue and hormone secretion.
This study found, however, that copper can accumulate in the brain and cause the blood-brain barrier - which controls what enters and exits the brain - to break down, resulting in the accumulation of the protein amyloid beta, which has been linked to Alzheimer's disease.
The findings were published in the journal Proceedings of the National Academy of Sciences.
Although studies involving animals can be useful, they frequently fail to produce similar results in humans.
The researchers said their results must be interpreted with caution, as the study did not prove a cause-and-effect relationship between copper exposure and Alzheimer's.
"Copper is an essential metal and it is clear that these effects are due to exposure over a long period of time," Deane said. "The key will be striking the right balance between too little and too much copper consumption. Right now we cannot say what the right level will be, but diet may ultimately play an important role in regulating this process."
The U.S. National Institute on Aging has more about Alzheimer's disease.