Exploring the nap paradox: are mid-day sleep bouts a friend or foe?

Abstract

The mid-day nap, sometimes called a siesta, is a ubiquitous occurrence across the lifespan. It is well established that in addition to reducing sleepiness, mid-day naps offer a variety of benefits: memory consolidation, preparation for subsequent learning, executive functioning enhancement, and a boost in emotional stability. These benefits are present even if a sufficient amount of sleep is obtained during the night prior. However, we present a paradox: in spite of these reported benefits of naps, frequent napping has also been associated with numerous negative outcomes (eg, cognitive decline, hypertension, diabetes), particularly in older populations. This association exists even when statistically controlling for relevant health- and sleep-affecting determinants. An emerging hypothesis suggests inflammation is a mediator between mid-day naps and poor health outcomes, yet further research is necessary. Given this, it may be premature to 'prescribe' naps as a health enhancer. Herein, we aggregate findings from several branches of sleep research (eg, developmental neuroscience, cognitive neuroscience, sleep medicine) to critically examine the paradoxical role of naps in cognitive and somatic health. This review uncovers gaps in the literature to guide research opportunities in the field.

Keywords: Cognition; Emotion; Inflammation; Learning; Memory; Nap.

Figure 1

Nap architecture from infancy to older adulthood. Dimmed region represents extrapolated data. [,,,–126]

Figure 2

Adenosine, one of the so called “sleep factors,” is thought to accumulate and dissipate depending on the state [34]. SD = sleep deprivation; SR = sleep restriction.

Figure 3

Nap architecture impacts immediate and long-term sleepiness following a nap. A brief nap with ligher sleep stages (NREM1 and NREM2) reduces sleepiness immediately after the nap, while a nap containing SWS may bring on sleep inertia [7,8]. However, there is a delayed benefit of naps that contain SWS. After sleep inertia has dissipated, sleepiness is lower for longer.

Figure 4

The potentiated synaptic burden accumulates with wakefulness, while encoding potential decreases. The mid-day nap reduces this burden and enhances future learning. In this way, a mid-day nap facilitates learning in 2 ways: through global downscaling (as in the synaptic homeostasis hypothesis [77]), and by boosting subsequent learning potential [19].