Should Neurologists Be Concerned With REM Sleep Quantity?

The association between sleep and overall health and well-being has long been of interest to physicians, researchers, and the general public. At the highest level, a simple U-shaped association between total sleep time and mortality has been described from as early as 1964. Those who sleep approximately 7 hours are at the lowest point in the curve, with the lowest mortality risk. Mortality increases incrementally as one moves in either direction on the curve, with a marked rise for those sleeping less than 4 hours or more than 10 hours. This association holds true for both sexes and across races/ethnicities and continents.

The study by Leary et al in this issue of JAMA Neurology expands our understanding of this association by evaluating the link between a specific sleep stage, rapid eye movement (REM), and mortality. Neurologists are most familiar with REM sleep because of the high prevalence of REM sleep behavior disorder and the association with neurodegenerative α-synucleinopathies. Epilepsy specialists are aware that REM sleep has been implicated in the pathophysiology of sudden unexpected death in epilepsy, even though seizures exclusively in REM sleep are rare.4 Most neurologists may not have occasion to consider REM sleep in a clinical context beyond these specific situations.

The analysis by Leary et al draws on data from 2 different longitudinal studies, the Osteoporotic Fractures in Men (MrOs) and Wisconsin Sleep Cohorts. They controlled for multiple confounders, including obstructive sleep apnea (OSA) and medication outcomes. The association between reduced REM sleep and mortality was seen with both absolute time in REM sleep and percentage of time in REM sleep. Although association does not imply causation, the finding that a lower proportion of REM sleep was associated with a higher all-cause mortality should interest neurologists, because it raises the question of whether REM sleep in an individual patient could serve as a biomarker for general health.