Diurnal naps and sleep interruption as precipitating factors of sleep paralysis in elite Japanese athletes

doi:10.21203/rs.3.rs-2759990/v1

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Diurnal naps and sleep interruption as precipitating factors of sleep paralysis in elite Japanese athletes

https://doi.org/10.21203/rs.3.rs-2759990/v1

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Background

Sleep paralysis and hypnagogic hallucinations are observed during sleep-onset rapid eye movement (REM) periods (SOREMPs). SOREMPs are associated with sleep pattern disruption. This study aimed to assess the occurrence of sleep paralysis and several sleep parameters in elite athletes and control groups to determine the relationship between sleep paralysis and specific sleep characteristics.

Methods

Eighty-four (47 male) elite and 116 (49 male) non-athletes (controls) were recruited. A questionnaire regarding the occurrence of sleep paralysis and several sleep parameters was administered.

Results

A relationship between sleep paralysis and long diurnal nap frequency was revealed. A small proportion (6.5%) of participants with sleep paralysis did not routinely take long naps, while 24.3% of those without sleep paralysis did not routinely take long naps. This proportion was rather striking in athletes compared with that in non-athletes. Participants with sleep paralysis experienced more frequent sleep interruptions than those without sleep paralysis, a difference that was more pronounced in athletes than in non-athletes.

Conclusion

The prevalence of sleep paralysis was reported to be high among elite Japanese athletes and non-athletes, a finding that is in accordance with previous reports. Long nap routines and sleep interruptions are closely associated with sleep paralysis, especially in elite athletes. A lengthy nap routine is sometimes recommended for sleep loss compensation, especially among elite athletes; however, since the occurrence of sleep paralysis may be a sign of sleep-wake rhythm disruption, caution is suggested when recommending long nap routines, even to athletes.

Elite Athletes

Sleep Paralysis

Diurnal Naps

Sleep Interruptions

Sleep paralysis is generally described in terms of its association with narcolepsy. Indeed, it was considered one of the components of the narcolepsy tetrad (i.e., sleep attack, cataplexy, sleep paralysis, and hypnagogic hallucinations). Although sleep paralysis is frequently associated with other narcoleptic syndromes, it also occurs independently, without sleep attack or cataplexy, in otherwise healthy individuals. Sleep paralysis occurring in healthy individuals is referred to as “isolated sleep paralysis” [1]. To date, only one study has investigated sleep paralysis among athletes. Liu et al. (2018) [2] surveyed 189 student athletes regarding their experience with respect to sleep paralysis and hypnagogic hallucinations and found that 25% and 35% of athletes experienced sleep paralysis and hypnagogic hallucinations, respectively. They considered the prevalence of both to be high among athletes and found that athletes who experienced sleep paralysis or hypnagogic hallucinations had significantly increased depression scores.

Sleep paralysis and hypnagogic hallucinations are observed during unusual occurrences of REM sleep, sleep-onset REM periods (SOREMPs) [3–6]. SOREMPs tend to occur under conditions of sleep pattern disruption, for example, after interruption of nocturnal sleep [6, 7], acute reversal of sleep and wakefulness [8], or during diurnal naps [9]. Several studies have reported that many athletes routinely take diurnal naps [9–12]. To assess risk of sleep paralysis among elite athletes, the authors surveyed both athletes and non-athletes regarding their experience with respect to sleep paralysis and several sleep parameters (usual bedtime, long nap routine, nocturnal sleep interruption, and fear of sleep paralysis).

Participants

Eighty-four elite athletes (47 males, mean age: 23.8 ± 6.45) were recruited, including 60 international- or national-level athletes, 12 junior international- or junior national-level, and 2 professionals. Among these, eight athletes had participated in national championships within the past year, and two were inter-collegiate level athletes. In addition, 116 (49 males) non-athlete participants (mainly managing staff of the Japan Institute of Sports Sciences and undergraduate students of Edogawa University; mean age: 20.89 ± 4.89) were recruited as controls. As two university students reported that they were once selected as certified athletes, they were excluded from the analysis. Approval for this study was obtained from the Research Ethics Committees of the Japan Institute of Sports Sciences (028) and Edogawa University (R04-003A). Written informed consent was obtained from all participants. For athletes under the age of 18 years, written informed consent was additionally obtained from their parents.

Procedures

A questionnaire that assessed each participant’s experience regarding the occurrence of sleep paralysis and several sleep parameters (usual bedtime, nocturnal sleep interruption, and fear of sleep paralysis) was administered using either a paper-based or web questionnaire. The authors asked about sleep paralysis frequency using the question “Have you ever experienced kanashibari?”. The word ‘kanashibari’ is a Japanese synonym for sleep paralysis [13]. Sleep paralysis frequency was assessed using questions with the following seven possible answers: never, once in a lifetime, two or three times in a lifetime, several times in a lifetime, several times per year, several times per month, or several times per week. Long nap frequency was assessed via the question, “Do you take naps longer than 30 min during daytime?”. The question had the following four possible answers: never, rarely, sometimes, or frequently. Nocturnal sleep interruption was assessed by asking the following question: “Do you wake up at night and have trouble sleeping (or not sleeping) for a while?”. The question had the following four possible answers: never, rarely, sometimes, or frequently. In the web-based survey, bedtime was assessed based on 30-min increments; however, a free format was used for the paper-based survey. Nonetheless, nearly all answers were given in 30-min increments.

Statistical Analyses

We conducted a chi-square analysis. The IBM SPSS Statistics ver. 25 software was used for the analysis. Values of P < 0.05 were considered statistically significant.

Prevalence of sleep paralysis in athletes and non-athletes

In Table 1, frequencies of sleep paralysis among athletes and non-athletes are shown. The study revealed that sleep paralysis occurred at a higher frequency among athletes than among non-athletes; however, the difference between the two groups was not significant (χ²= 7.423, df = 6, p = 0.284).

Long nap frequency in athletes versus non-athletes

Table 2 shows frequencies of diurnal naps among athletes and non-athletes. The data indicate that long nap frequencies were higher among athletes versus non-athletes. However, the difference was not significant (χ²= 2.933, df = 3, p = 0.402).

Sleep interruption in athletes and non-athletes

Table 3 shows frequencies of sleep interruption among athletes and non-athletes. Findings revealed that similar levels of sleep interruption occurred in both groups. Further, comparison of sleep interruption frequency revealed no statistical difference between the groups (χ²= 0.942, df = 3, p = 0.815).

Sleep paralysis and long nap frequency

The relationship between sleep paralysis [SP (-) and SP (+) designate ‘no experience’ and ‘at least one experience’, respectively] and long diurnal nap frequency is detailed in Table 4. A very small proportion (6.5%) of participants with sleep paralysis did not routinely take long naps, while 24.3% of those without sleep paralysis did not routinely take long naps. A between-group comparison revealed that the nap frequency of groups differed significantly (χ² = 12.521, df = 3, p = 0.006). Similar patterns were observed when athlete and non-athlete data were examined individually; however, the difference was more striking among athletes than among non-athletes. In fact, only among athletes was the difference between nap frequency among those with and without sleep paralysis statistically significant (athlete group: χ²= 10.706, df = 3, p = 0.013; control group: χ²= 3.996, df = 3, p = 0.262).

Sleep paralysis and sleep interruption

Table 5 shows the relationship between sleep paralysis and the frequency of sleep interruption. Participants with sleep paralysis experienced sleep interruption more frequently than those without, a difference that was statistically significant (χ²= 11.077, df = 3, p = 0.011). A similar pattern was observed when analyses were conducted separately in the athletes and non-athletes. However, the difference was more striking among athletes than among non-athletes. In fact, between-group differences were only statistically significant among the athlete group (athletes: χ²= 7.991, df = 3, p = 0.046; non-athletes: χ²= 5.254, df = 3, p = 0.154).

Sleep paralysis and bedtime

A comparison of bedtimes of participants with and without sleep paralysis revealed no significant differences between groups. This was true when all participants, athletes, and non-athletes were considered (all participants: t = 1.110, df = 198, p = 0.268; athletes: t = 0.808, df = 82, p = 0.422; control group: t = 1.376, df = 114, p = 0.171; Table 6).

Here, the prevalence of sleep paralysis was determined to be high among both elite Japanese athletes and non-athletes. This finding agrees with results from several surveys conducted in Japan and elsewhere, which have shown that the prevalence of sleep paralysis is high (approximately 40%) [13–17]. Athletes, in particular, are known to take long naps [10]. This study showed that routinely taking long naps and experiencing sleep interruption were closely associated with the occurrence of sleep paralysis, especially in elite athletes.

A long nap routine disrupts the sleep and wakefulness cycle and causes several undesirable consequences [18, 19]. The reason that routinely taking naps and sleep paralysis are associated may be related to the duration of each nap episode. We did not ask participants about the typical duration of their naps; therefore, further studies will be needed to determine whether nap duration affects the occurrence of sleep paralysis. Sleep interruption (waking after sleep onset) is also considered a sign of sleep and wakefulness cycle disruption [20]. Liu et al. [1] showed that sleep paralysis is associated with depression. Therefore, the possibility of depression should be considered if a person experiences sleep paralysis. Generally, the sleep paralysis phenomenon may be a sign of sleep and mental health problems.

Routinely taking long naps is sometimes recommended to compensate for the loss of sleep, especially among athletes [11, 21]; however, the occurrence of sleep paralysis is a sign of sleep and wakefulness rhythm disruption. Therefore, caution is needed when recommending lengthy naps to athletes.

REM

Rapid eye movement

Sleep paralysis

SOREMP

Sleep-onset rapid eye movement period

Data Availability

The datasets analyzed in the current study are not publicly available due to the protection of the privacy of the participants but are available from the corresponding author upon reasonable request.

Ethics approval and consent to participate: All procedures performed in the study involving human participants were in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This study was approved by the Research Ethics Committees of the Japan Institute of Sports Sciences (028) and Edogawa University (R04-003A). Written informed consent was obtained from all of the participants. For athletes under the age of 18 yrs, written informed consent was obtained from their parents.

Consent for publication: Not applicable.

Competing interests:The authors declare that they have no competing interest.

Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Author contributions:

All authors contributed to the study conception and design. MH and KF performed the material preparation, data collection and analysis. KF wrote the first draft of the manuscript and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgements: We thank all the participants for their commitments.

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Tables 1 to 6 are available in the Supplementary Files section.

No competing interests reported.

Tables.docx

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Version 1

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Diurnal naps and sleep interruption as precipitating factors of sleep paralysis in elite Japanese athletes

Status:

Version 1

Abstract

Background

Methods

Participants

Procedures

Statistical Analyses

Results

Discussion

Conclusions

List Of Abbreviations

Declarations

References

Tables

Additional Declarations

Supplementary Files

Status:

Version 1