Mental decline starts before Alzheimer's

When Alzheimer's disease actually starts is often not clear, but it now appears that it may be preceded by rapid cognitive decline for up to six years before it becomes evident.

This accelerated weakening of memory and other mental function is not seen in people who do not develop the disease. Alzheimer's disease has a much longer course and affects substantially more people than generally recognised.

Researchers in United States evaluated information on 2,071 older adults without dementia who took part in two separate studies, including 1,511 who had no signs of cognitive impairment. The participants were tested on specific cognitive functions such as working memory, perceptual speed and visuo-spatial ability. During 16 years of follow-up, 462 people developed Alzheimer's disease.

It was found that dementia in Alzheimer's disease is preceded by an average of five to six years of rapid cognitive decline. In fact, the rate of cognitive decline in these participants accelerated more than 15-fold. Also, the precursor of Alzheimer's disease, mild cognitive impairment, is preceded by about six years of increased cognitive decline. In contrast, little cognitive decline was evident in people who did not develop these conditions.

The above results provide further evidence of the magnitude of the public health problem posed by Alzheimer's disease and related disorders and underscore the importance of developing strategies to delay its onset. Being able to predict which people were more likely to develop Alzheimer's would save a lot of time and money and future research could test emerging prevention strategies in people with this type of accelerating early decline. How well a treatment slows an early rate of decline may be useful in predicting prevention methods that work.