New York, Mar 18 (IANS): Longer and more frequent daytime napping among older adults maybe linked with poor cognitive performance - a sign of Alzheimer's disease, claims a study.

In the study conducted over 1,000 adults with an average age of 81, published in Alzheimer's and Dementia: The Journal of the Alzheimer's Association, longer or more frequent daytime napping in a specific year predicted worse cognitive performance in the following year, and vice versa.

"Daytime sleep behaviours of older adults are often ignored, and a consensus for daytime napping in clinical practice and health care is still lacking," said Peng Li, from Division of Sleep and Circadian Disorders at Brigham and Women's Hospital in the US.

"Our results not only suggest that excessive daytime napping may signal an elevated risk of Alzheimer's dementia, but they also show that faster yearly increase in daytime napping may be a sign of deteriorating or unfavored clinical progression of the disease.

"Our study calls for a closer attention to 24-hour sleep patterns - not only night-time sleep but also daytime sleep for health monitoring in older adults," Li said.

Studies on daytime napping in older adults have had conflicting results, with showing that daytime napping has benefits on acute cognitive performance, mood, and alertness, others have highlighted the adverse outcomes on cognitive performance.

In the current study, the team tested two hypotheses: participants nap longer and/or more frequently with ageing and the changes are even faster with the progression of Alzheimer's; and participants with excessive daytime napping are at an increased risk of developing the disorder.

The participants were provided a watch-like device called Actical, to wear on their non-dominant wrist for up to 14 days. The team identified sleep episodes using a previously validated sleep scoring algorithm that considers wrist activity counts. After napping episodes were identified, the nap duration and frequency were calculated.

Independent of known risk factors for dementia, including age and night-time sleep duration and fragmentation, longer and more frequent daytime naps were a risk factor for developing Alzheimer's dementia in cognitively normal older men and women.

Besides, annual increases in napping duration and frequency were accelerated as the disease progressed, especially after the clinical manifestation of Alzheimer's. Ultimately, the authors describe the relationship between daytime napping and cognition to be a "vicious cycle."