CHICAGO, Jan. 29 (Xinhua) -- Body clock disruptions occur years before memory loss for people with Alzheimer's disease, U.S. researchers at Washington University in St. Louis found.

The researchers tracked circadian rhythms in 189 cognitively normal, older adults with an average age of 66. Some had positron emission tomography (PET) scans to look for Alzheimer's-related amyloid plaques in their brains. Others had their cerebrospinal fluid tested for Alzheimer's-related proteins. And some had both scans and spinal fluid testing.

Fifty of the 139 participants who either had abnormal brain scans or abnormal cerebrospinal fluid all experienced significant disruptions in their internal body clocks, showed the study published Monday in the journal JAMA Neurology.

The study participants, from Washington University's Knight Alzheimer's Disease Research Center, all wore devices similar to exercise trackers for one to two weeks. Each also completed a detailed sleep diary every morning.

By tracking activity during the day and night, the researchers could tell how scattered rest and activity were throughout 24-hour periods. Participations who experienced short spurts of activity and rest during the day and night were more likely to have evidence of amyloid buildup in their brains.

The researchers also conducted a separate study in mice showing that similar circadian disruptions accelerate the development of amyloid plaques in the brain, which are linked to Alzheimer's.

The researchers hold that it's too early to answer the chicken-and-egg question of whether disrupted circadian rhythms put people at risk for Alzheimer's disease or whether Alzheimer's-related changes in the brain disrupt circadian rhythms.

But the study could at least help doctors identify people at risk of Alzheimer's earlier than currently is possible. This is important because Alzheimer's damage can take root in the brain 15 to 20 years before clinical symptoms appear.