Elsevier

Physiology & Behavior

Volume 96, Issues 4–5, 23 March 2009, Pages 513-517
Physiology & Behavior

Self-reported ‘sleep deficit’ is unrelated to daytime sleepiness

https://doi.org/10.1016/j.physbeh.2008.11.009Get rights and content

Abstract

Seemingly, many healthy adults have accrued a sleep debt, as determined by findings based on the multiple sleep latency test (MSLT). However, our recent, extensive survey found self-reported sleep deficit was not linked to daytime sleepiness determined by the Epworth sleepiness scale (ESS). Here, we report on the link between self-reported sleep deficit and gold standard measures of sleepiness: MSLT, Psychomotor vigilance test (PVT) and Karolinska Sleepiness Scale (KSS). Habitual sleep time in forty-three participants, from using a week long sleep diary and actiwatch data, compared with self-ratings of how much sleep they needed, provided estimates of apparent sleep deficit or otherwise. They were split into categories: ‘sleep deficit’ (Av. − 47 min), ‘sleep plus’ (Av. 47 min) or ‘neutral’ (Av. 0 ± 15 min), depicting perceived shortfall (or excess) sleep. Although the deficit group desired to sleep longer than the other groups, they actually obtained similar habitual nightly sleep as the neutral group, but less than the sleep plus group. ‘Survival curves’ based on those falling asleep during the MSLT showed no difference between the groups. Neither was there any difference between the groups for the PVT, KSS, or ESS. Here, factors other than sleepiness seem to influence self-perceived sleep deficits.

Introduction

Sleep debt is apparently becoming endemic in modern society [23], [10], [11], [18], seemingly because of increasing waking demands. Laboratory evidence seems to further indicate this [4], [3], with, for example, 8 h in bed considered inadequate due to observed neurobehavioural deficits [25].

Population studies over the last 40 years have consistently shown average daily sleep for UK healthy adults to be 7–7.5 h [24], [17], [13], [2]. Nevertheless, this would seem to be inadequate [25], and as such society may be harbouring a hidden sleep debt. Whilst the individual desire for more sleep may be due to many healthy adults perceiving themselves to have insufficient sleep, our previous research based on 10,810 UK adults [2], suggested that this desire depends on the type of questions asked of respondents and, for a sizeable portion, that their perceived sleep deficit was synonymous with wanting more ‘time-out’, rather than more sleep per se. Moreover, self-reported sleep deficit was unrelated to daytime sleepiness (Epworth sleepiness scale — ESS) [15] but more closely linked with perceived ‘stress’. Interestingly, as a probe for the strength of desire for more sleep, and given the choice of extra daily sleep or relaxing waking activities, most of those with an apparent sleep deficit opted for the latter. That is, although they would like more sleep they would not forfeit ‘free-waking time’ to take this sleep.

As one might expect, short sleepers (6–7 h/night) are more likely to have a genuine sleep debt due to voluntary curtailment of sleep [16], and are more likely to have MSLT scores of less than 5 min, deemed to be ‘pathologically’ sleepy (cf. [21], [4]). Despite such a MSLT score being likely to be associated with performance degradation and unintentional sleep episodes (cf. [6], [4], [8], subjectively, sleepiness is often not reliably reported by participants [5], [25]), who may be in denial about their sleepiness.

Ascertaining actual sleep need is difficult outside of the laboratory and reported shortfall of sleep is usually based on introspection. Although our findings [2] may have, in part, been distorted by this confound, the ESS, helps overcome this problem by gauging actual incidents of falling asleep. Nevertheless, more objective measures of habitual sleep duration alongside gold-standard measures of daytime sleepiness may provide further insight into the link between desire for more (or less) sleep and daytime sleepiness.

In a controlled laboratory environment we investigated whether a perceived desire for extra sleep, based on comparisons with actigraphically measured habitual sleep times, is associated with increased daytime sleepiness, as determined by objective measures of sleepiness including the ‘gold standard’ MSLT and psychomotor vigilance test (PVT) e.g. [8] or whether it might be linked to factors other than sleepiness (e.g. anxiety).

Section snippets

Participants

Forty-three healthy young (26.3 y ± 4.2 y) male (n = 19) and female (n = 24) participants were recruited after screening thus: via questionnaire to exclude those who were nappers (≥ 2/week); were not extreme ‘morning’ or ‘evening’ types; consumed less than 150 mg caffeine daily and less than 20 units alcohol weekly; without any sleep or medical problems other than minor illnesses; were not on any medication causing daytime sleepiness. Random drug (urine) testing ensured all participants were free from

Results

Groups were split according to their HST and PSN as per Table 1. Paired t-tests for each group confirmed the sleep deficit group had a significantly negative discrepancy between HST and PSN (t =  7.930, df. 11, p < 0.0005) as they desired more sleep. The HST and PSN for the neutral group did not differ (p = 0.898) and the sleep plus group felt they needed significantly less sleep than they took (t = 5.976, df. 17, p < 0.0005).

There were no significant differences between the groups for age (p = 0.992) or

Discussion

Those who desire more sleep (apparent sleep deficit) had significantly shorter HSTs than those who perceived their sleep to be in excess of need (7.29 h vs. 7.58 h). However, neither group differed from the control group (7.41 h). Despite the sleep deficit group sleeping at the average UK 7.5 dh norm [2], [13], [24], [17] their perceived sleep need was significantly higher (8.16 h) than the neutral (7.41 h) and sleep plus (7.08 h) groups.

Our previous research [2] addressed why individuals

Acknowledgments

This study was funded by the Economic and Social Research Council, Ref: RES-000-23-0954. The authors would like to thank Kate Jordan for her help with data collection.

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