By DAVID DERBYSHIRE

Last updated at 23:59 09 January 2008

Children exposed to lead in old paint, Victorian water pipes and unsafe toys could be at risk of Alzheimer's later in life, scientists have said.

A study shows that even small amounts of the dangerous metal in the first few years can cause changes in the brain associated with the devastating disease.

Although lead has been banned in petrol and paint, it is still present in older buildings.

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Last year, millions of toys imported from China were recalled after tests showed they were made with lead paint. The Alzheimer's Society warned, however, against overreacting to the findings, which came from a study of monkeys.

A spokesman said there was no proof that lead exposure caused the disease.

The U.S. researchers behind the study say their work shows that lead has toxic side effects that can appear decades after children are exposed.

"We're not saying that lead exposure causes Alzheimer's disease, but it's a risk factor," Dr Nasser Zawia of the University of Rhode Island in Kingston told the New Scientist.

His team fed infant formula milk laced with low doses of lead to baby monkeys - and then followed their progress for 23 years.

Although the animals did not show any symptoms of dementia, a post mortem of their brains revealed plaques - harmful deposits of protein normally found in Alzheimer's patients.