THURSDAY, Aug. 11 (HealthDay News) -- Symptoms of Alzheimer's disease may be harder to detect in people over 80, according to a new study that examined the relationship between age-related brain shrinkage and Alzheimer's-associated memory loss.

The study included 105 Alzheimer's patients and 125 dementia-free people who were grouped according to age, those 60 to 75 (young-old) and those 80 and older (very old).

The participants underwent brain scans and were given tests to assess language, attention and information processing speed, executive function, and short and longer term memory.

People in both groups had similar levels of overall cognitive impairment, but the pattern of changes associated with Alzheimer's disease seemed to be less noticeable in very-old patients than in the young-old.

Compared to the dementia-free participants in their age groups, the executive function, immediate memory and attention-processing speed in very old Alzheimer's patients was less abnormal than in young-old patients.

The study also found that very-old Alzheimer's patients had less severe thinning of certain areas of the cerebral cortex and the overall cerebellum than young-old patients.

The thickness of these brain areas decreases with age, so there are fewer differences between the brains of very-old healthy people and very-old Alzheimer's patients, the researchers noted.

The study appears in the Aug. 10 online issue of the journal Neurology.

"Those who are 85 and older make up the fastest growing population in the world," study author Mark Bondi of the University of California San Diego School of Medicine and VA San Diego Healthcare System said in a journal news release. "Our study shows how age has a dramatic effect on the profile of brain atrophy and cognitive changes evident in Alzheimer's disease."

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about Alzheimer's disease.