Alzheimer's disease progresses faster in people who are highly educated, new research has suggested.
Past studies have found that high levels of education may help ward off the dementia caused by Alzheimer's.
But new research, published in the Journal of Neurology, Neurosurgery and Psychiatry, found that high educational attainment may also speed up the progression of Alzheimer's once it has developed.
The team, from Columbia University Medical Centre in New York, studied 312 patients over the age of 65 who had all been diagnosed with Alzheimer's. These New Yorkers were monitored for five years, undergoing various assessments of brain function.
The researchers, led by Dr Nicolaos Scarmeas, found that the overall mental agility of all the patients declined every year. But for each extra year of education the patients received, there was an additional 0.3 per cent deterioration.
The speed of thought processes and memory appeared to be particularly affected by higher levels of education.
The researchers said their findings remained the same even when other factors such as age, depression and vascular disease, which are likely to affect brain function, were taken into account.
The team said that one possible explanation for the results was "cognitive reserve" theory, which suggests that the brain's ability to cope with Alzheimer's varies between different people.