"From a clinical standpoint, even mild loss of cognitive function in older people should not be viewed as normal, but as an indication of a disease process," Dr David Bennett, director of the Rush Alzheimer's Disease Centre in Chicago, noted in university statement.

"In particular, family members need to know that the patient has a real problem and that his behaviour is not due to normal ageing nor is he simply not paying attention," he added.

In the medical journal Neurology, Bennett and colleagues describe 180 elderly Catholic clergy, participants in the Religious Orders Study of ageing and dementia who agreed to annual mental tests beginning in 1993 and brain autopsy when they died.

At the time of death, 37 had mild cognitive impairment, 83 had dementia, and 60 had no cognitive difficulties.

Of the 37 with mild cognitive impairment, 23 showed brain pathology consistent with probable or definite Alzheimer's disease, and 12 had areas of brain tissue due to loss of blood supply, the investigators report.

Moreover, even among the 60 individuals without cognitive impairment, 28 showed evidence of probable or definite Alzheimer's disease.

A third unaffected

Nonetheless, the researchers add, it is worth noting that one third of the group, whose average was more than 80 years, did not experience cognitive decline over several years of follow-up, despite having a significant amount of Alzheimer's disease damage.

This finding suggests that some individuals may have some type of mental reserve capacity that allows them to escape the loss of memory despite the accumulation of brain disease, Bennett's team notes.

It also supports other data suggesting that the elderly can live to advanced old age with their cognitive faculties intact, and implies that loss of memory is not an inevitable part of ageing but rather a consequence of age-related diseases.

Therefore, evidence of memory loss at any age "should be taken seriously by individuals, family members, and healthcare professionals alike", the researchers write.

"Although there are no medications currently approved for the symptomatic treatment of mild cognitive impairment, there are things one can do to improve the environment and make it 'more friendly' to persons with memory loss," Bennett said.