Problems related to sleep are common among the estimated 4.5 million Americans suffering from Alzheimer's disease.

The disruptions in restful sleep often depend on the stage of the dementia, with those early in the disease process often sleeping more than usual and awakening disoriented. In the advances stage of the disease, the person may sleep during the day and have disrupted sleep at night with frequent awakenings. There can also be nighttime wanderings and agitation.

But it is not just the quantity of sleep that can be affected but also the quality of sleep. In order to have restful healing sleep, a person needs to cycle into REM sleep. This type of sleep is characterized by a rapid eye movement pattern.

Quality sleep occurs in patterns and distinct phases. Sleep begins with a light sleep starting and lasting 5 to 10 minutes, followed by a phase in which the heart rate slows and the body temperature drops in preparation for deep sleep. The final non-REM stage is deep sleep, and during this period the body repairs and regenerates tissue, strengthens the immune system and builds muscle and bone.

REM sleep usually starts about 90 minutes into sleep and lasts about 10 minutes. The sleep cycle repeats itself throughout the night with each successive cycle having longer episodes of REM sleep.

The amount of time spent in different phases changes over the years, with less deep sleep as you age. Infants can spend up to 50 percent of their sleeping time in REM sleep, whereas healthy adults spend about 20 percent of their sleep time in an REM phase.

A recent study found that the REM phase of sleep is abnormally short in those with Alzheimer's disease. The study was led by Matthew P. Pase, Ph.D., from the Department of Neurology at Boston University School of Medicine.

The researchers looked at cases of Alzheimer's disease that had been offspring participants in the Sleep Heart Study and were over the age of 60 at the time of the sleep assessment. Sleep stages had been recorded using home-based polysomnography.

The participants were followed for up to 19 years after the study. They observed 32 cases of dementia, of which 24 were considered Alzheimer's disease. They found that the earlier documentation of lower REM sleep percentage and longer REM sleep latency had been a risk factor for subsequent dementia.

For a percentage reduction in REM sleep, there was an associated 9 percent increased risk of dementia. The risk held when the confounders of age, sex and vascular problems were controlled for.

"Sleep disturbances are common in dementia, but little is known about the various stages of sleep and whether they play a role in dementia risk," Pase said. "We set out to discover which stages of sleep may be linked to dementia, and while we did not find a link with deep sleep, we did with REM sleep.

"Our findings point to REM sleep as a predictor of dementia. The next step will be to determine why lower REM sleep predicts a greater risk of dementia. By clarifying the role of sleep in the onset of dementia, the hope is to eventually identify possible ways to intervene so that dementia can be delayed or even prevented."

A good night of rest benefits babies, teenagers, adults and the elderly. We all hope to move through our advanced twilight years free of dementia. It appears that disruptions in sleep and poor sleep behaviors can be a predictor of the quality of the days of during those twilight years.