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2021 The Korean Society of Sleep Medicine 1
pISSN 2093-9175 / eISSN 2233-8853
Sleep Med Res 2021 Jun 2 [Epub ahead of print]
ORIGINAL ARTICLE
Background and ObjectiveaaPatients with position-dependent obstructive sleep apnea have a
> 2-fold higher apnea-hypopnea index when sleeping in a supine position compared with a non-
supine position. We investigated the eect of body pillow use on sleeping body position and sleep
architecture in healthy young adults.
MethodsaaIn experiment 1, we evaluated the body pressure distribution with or without body
pillow use in 8 healthy young adults [age, 36.5 ± 13.0 years; body mass index (BMI); 20.6 ± 1.2 kg/
m2]. In experiment 2, we performed a randomized-crossover intervention study to evaluate the ef-
fects of body pillow use on sleeping position and sleep architecture in 10 healthy young adults (age,
24.3 ± 7.8 years; BMI, 21.4 ± 1.7 kg/m2). Sleep architecture was characterized by polysomnogra-
phy, and body positions were monitored using a sensor. Subjective sleep quality was evaluated with
the Oguri-Shirakawa-Azumi sleep inventory, middle age and aged version.
ResultsaaIn experiment 1, body pillow use significantly reduced mean body pressure on the
shoulder, hip, and whole body. In experiment 2, mean time spent in the supine, lateral, and prone
body positions did not dier signicantly between the 2 trials. Body pillow use, however, signi-
cantly extended the sustained time spent in the lateral body position compared with the control
trial. Subjective sleep quality and sleep architecture did not dier signicantly between the 2 trials,
but body pillow use decreased the number of short (30 s) slow-wave sleep episodes.
ConclusionsaaSleeping with a body pillow eectively extends sustained time in a lateral sleeping
position and prevents segmentation of slow-wave sleep episodes.
Sleep Med Res
Key Wordsaa
Body pillow, Sleeping body position, Lateral position, Sleep architecture,
Energy expenditure.
INTRODUCTION
Obstructive sleep apnea (OSA) is a common sleep-linked breathing disorder characterized by
recurrent episodes of upper airway disruption during sleep [1]. Eective treatment of OSA re-
duces medical risk factors associated with cardiovascular and cerebrovascular disease, and met-
abolic syndrome [2,3]. Current guidelines recommend continuous positive airway pressure
(CPAP) as the gold standard for managing the clinical state of OSA [4]. CPAP improves sleep
quality, subjective or/and objective daytime sleepiness, and mood, especially in those with se-
vere OSA [5]. e use of CPAP decreases complaints of excessive daytime sleepiness and func-
tional impairment due to hypersomnolence [6,7]. In patients with OSA, CPAP decreases the
sleep latency, the percent time in non-rapid eye movement (NREM) stage 1, the arousal index,
https://doi.org/10.17241/smr.2021.00878
Eects of Body Pillow Use on Sleeping Posture
and Sleep Architecture in Healthy Young Adults
Insung Park, PhD1, Chihiro Suzuki, MMSc1, Yoko Suzuki, PhD, RPSGT1, Fusae Kawana, BSc, RPSGT1,2,
Katsuhiko Yajima, PhD3, Shoji Fukusumi, PhD1, Toshio Kokubo, PhD1, Kumpei Tokuyama, PhD1,
Masashi Yanagisawa, MD, PhD1, Makoto Satoh, MD, PhD1
1International Institute for Integrative Sleep Medicine (WPI-IIIS), University of Tsukuba, Ibaraki, Japan
2Cardiovascular Respiratory Sleep Medicine, Juntendo University Graduate School of Medicine, Tokyo, Japan
3Faculty of Pharmaceutical Sciences, Josai University, Saitama, Japan
Received: February 8, 2021
Revised: March 19, 2021
Accepted: March 24, 2021
Correspondence
Makoto Satoh, MD, PhD
International Institute for Integrative Sleep
Medicine (WPI-IIIS),
University of Tsukuba, 1-2 Kasuga, Tsukuba,
Ibaraki 305-8550, Japan
Tel +81-29-859-1858
Fax +81-29-859-1290
E-mail satoh.makoto.fu@u.tsukuba.ac.jp
ORCID
Insung Park
https://orcid.org/0000-0001-6389-1937
Chihiro Suzuki
https://orcid.org/0000-0002-7272-0299
Yoko Suzuki
https://orcid.org/0000-0001-7957-1743
Fusae Kawana
https://orcid.org/0000-0003-2227-0549
Katsuhiko Yajima
https://orcid.org/0000-0002-8199-9981
Shoji Fukusumi
https://orcid.org/0000-0002-0641-9799
Toshio Kokubo
https://orcid.org/0000-0002-9098-3690
Kumpei Tokuyama
https://orcid.org/0000-0003-1756-4227
Masashi Yanagisawa
https://orcid.org/0000-0002-7358-4022
Makoto Satoh
https://orcid.org/0000-0002-2723-8153
cc is is an Open Access article distributed un-
der the terms of the Creative Commons Attribu-
tion Non-Commercial License (https://creative-
commons.org/licenses/by-nc/4.0) which permits
unrestricted non-commercial use, distribution,
and reproduction in any medium, provided the
original work is properly cited.
2 Sleep Med Res
Body Pillow Use and Sleeping Posture
Sleep Med Res 2021 Jun 2 [Epub ahead of print]
and the respiratory disturbance index, and increases the per-
cent time in NREM stage 2, thereby also aecting the sleep ar-
chitecture [8,9]. Although CPAP is as an eective treatment for
upper airway obstruction in sleep apnea, the treatment is not
always tolerated and compliance with CPAP therapy is limited;
29% to 83% of patients are nonadherent [10]. e main reasons
for noncompliance with CPAP management are the side eects,
which include dry nose and mouth, sneezing, nasal congestion,
skin irritation, abrasions on the nose bridge, and eye irritation
from mask leaks [11].
Patients with position-dependent OSA (POSA) have a greater
than 2-fold higher apnea-hypopnea index (AHI) during sleep
in the supine position compared with a non-supine position
[12]. Patients with POSA are estimated to comprise 70% to 80%
of those with mild (AHI = 514 hr-1) and moderate OSA (AHI =
1529 hr-1), and approximately 56% to 75% of patients with se-
vere OSA (AHI ≥ 30 hr-1) [13-15]. In POSA, sleeping in the su-
pine position is associated with worse OSA [16], and many forms
of positional therapy have been developed in an attempt to im-
prove long-term adherence, e.g., chest-worn sleep position train-
ers, tennis ball technique, positional alarms, and verbal instruc-
tions urging patients to shi to a non-supine body position when
the supine body position is detected [17-19]. ese treatments
induce pain and discomfort, and subsequently disrupt the sleep
architecture, which also limit compliance. As an alternative meth-
od, a specially designed body pillow was developed to enforce
the lateral position, but its ecacy has not been evaluated [20].
e most likely reason for disrupting a lateral sleeping position
is excess body pressure distribution on the shoulder and hip [21].
We hypothesized that using a body pillow improves body pres-
sure distribution, which extends the duration of a sustained
lateral sleeping body position. In the present study, we evaluat-
ed the eect of body pillow use on sleeping body position, sleep
architecture, and sleeping energy metabolism in healthy young
adults.
METHODS
Protocol and Subjects
For experiment 1, we recruited 8 healthy young adults [mean
± standard deviation (SD) age 36.5 ± 13.0 years, mean body mass
index (BMI) 20.6 ±1.2 kg/m2] to evaluate the distribution of body
pressure in the supine, prone, and lateral sleeping positions. e
temporary body pressure distribution was measured in each
sleep position using an ERGOCHECK system (ABW Co. Ltd.,
Hamburg, Germany) in all participants. e measurements were
obtained with the participants awake and under the investiga-
tor’s specic instructions. An example of the body pressure dis-
tribution in each position is shown in Fig. 1.
Experiment 2 was a randomized-crossover intervention study
with or without body pillow use, which were separated a wash-
out period of more than 1 week. One week preceding the experi-
ment, the participants stayed in a whole room metabolic chamber
Fig. 1. Body pillow, body pressure distribution, and example of body pillow use during sleep. A: Body pillow used in this study. Participants
were provided the opportunity to choose the appropriate body pillow for their body volume among the S-, M-, and L-sized body pillows. B, C:
Examples of body pressure distribution without and with body pillow use. Each grid represents 5 × 5 cm. D: Example of body pillow use
during sleep in experiment 2. Note that 2 pillows were used, 1 on each side of the body.
50
40
30
20
10
0
50
40
30
20
10
0
mm Hg
mm Hg
A
D
B
C
90 cm
20–23 cm
Park I, et al.
www.sleepmedres.org 3
as an adaptation night, during which the sensors and electrodes
of the polysomnographic (PSG) recording system were attached
to the participants. ree days prior to the experiment, the par-
ticipants were instructed to maintain a constant 8 h sleep/16 h
wake schedule following their habitual bed and awake time and
to refrain from taking naps, which was conrmed by wrist ac-
tigraphy (ActiGraph, Ambulatory Monitoring, NY, USA), and
to complete daily diaries. Participants refrained from ingesting
caeine and alcohol for 1 week prior to the experiment. All par-
ticipants, 10 healthy young adults (4 male, 6 female), satised
the inclusion criteria: 20 to 65 years of age, BMI 18.5 to 25 (kg/
m2), a regular sleep/wake pattern, and not engaged in regular ex-
ercise more than twice a week. Exclusion criteria were as follows:
self-reported sleep problems (Pittsburgh Sleep Quality Index
score > 5); shiwork or transmeridian travel within 3 months
before the study; smoking; excessive alcohol intake (> 30 g/day);
currently taking medication for cardiovascular disease, hyper-
tension, diabetes, hypercholesterolemia, hyperglycemia, or hy-
perlipidemia; use of medications aecting sleep or metabolism;
and severe sleep apnea syndrome. e Morningness-Evening-
ness Questionnaire (MEQ) was administered to eliminate par-
ticipants having an extreme morning and evening type (41 <
MEQ scores < 59) [22].
On the experiment day, participants arrived at the laboratory
aer dinner. Electrodes for polysomnography and a body posi-
tion sensor were attached before the participants entered the
metabolic chamber where they remained sedentary until their
habitual sleep onset time. Participants went to bed at their habit-
ual bedtime and slept for 8 h. Participants responded to a ques-
tionnaire about subjective sleep quality aer waking the follow-
ing morning.
e study was conducted according to the guidelines for pro-
cedures involving human subjects put forth by the Declaration
of Helsinki, and the protocol was approved by the Ethics Com-
mittee of the University of Tsukuba (H30-284). All of the partici-
pants provided written informed consent before study initiation.
Body Pillow
e body pillow was designed to support the upper side of the
arm and leg to reduce body pressure on the lower side of shoul-
der and hip (Fig. 1). e body pillows (Nishikawa Co., Ltd., To-
kyo, Japan) were made from 100% polyester. All participants were
provided the opportunity to choose from among 3 body pillow
sizes according to their body volume (S: diameter 20 cm, length
90 cm, weight 1.19 kg; M: diameter 23 cm, length 90 cm, weight
1.4 kg; and L: diameter 26 cm, length 90 cm, weight 2.0 kg). e
subjects used 2 body pillows, with 1 positioned on each side of
the body (Fig. 1).
Polysomnography
e recording system (PSG-1100; Nihon Kohden, Tokyo, Ja-
pan) comprised 6 electroencephalography derivations (F3-M2,
F4-M1, C3-M2, C4-M1, O1-M2, and O2-M1), submental and
leg electromyography, bilateral electrooculogram, air ow at the
nose and mouth, chest and abdominal respiratory movement,
oxygen saturation at the ngertip, and a body position sensor
that was xed on the skin at the center of the sternum. Respira-
tory events such as the AHI and the oxygen desaturation index
(ODI) were scored according to the American Academy of Sleep
Medicine (AASM) criteria: apnea was dened as a drop in air-
ow of at least 90% from baseline lasting 10 s or longer. Hypop-
nea was dened as a > 30% drop in airow lasting at least 10 s,
associated with either a decrease in arousal or > 3% O2 satura-
tion drop [23]. The electroencephalography electrodes were
placed on the surface of the head in accordance with the inter-
national 1020 system, recording at the frontal (F3, F4), central
(C3, C4), and occipital (O1, O2) sites, and at 2 reference sites on
M1 and M2. Sleep parameters were scored in 30-s intervals as
wakefulness, and stages 1, 2, 3 [slow wave sleep (SWS)], and REM
sleep according to standard criteria of the AASM [23]. In addi-
tion, total sleep time, sleep onset latency, REM sleep latency, and
sleep eciency were evaluated. e body position sensor dis-
criminated among the 5 body positions; supine, prone, le later-
al, right lateral, and sitting. During the whole sleep period, body
positions were also monitored by an infrared camera.
Subjective Self-Reported Quality of Sleep
e Oguri-Shirakawa-Azumi sleep inventory, middle age and
aged version (OSA-MA) questionnaire was used to assess sub-
jective sleep quality aer waking in the morning [24]. is ques-
tionnaire comprises 16 items with 5 factors (“Sleepiness on ris-
ing,” “Initiation and maintenance of sleep,” “Frequent dreaming,”
“Refreshness,” and “Sleep length.”
Indirect Calorimetry
e airtight metabolic chamber measures 2.00 × 3.45 × 2.10 m
(FHC-15S; Fuji Medical Science Co., Ltd., Chiba, Japan), and
air in the chamber is pumped out at a rate of 80 L/min. e tem-
perature and relative humidity of incoming fresh air were con-
trolled at 25°C and 55%, respectively. e chamber is furnished
with desk, chair, and toilet. Concentrations of oxygen (O2) and
carbon dioxide (CO2) in the outgoing air were measured with
high precision by online process mass spectrometry (VG Prima
δB; ermo Electron Co., Winsford, UK). e precision of the
mass spectrometry, dened as the SD for continuous measure-
ment of the calibrated gas mixture (O2, 15%; CO2, 5%), was
0.0016% for O2 and 0.0011% for CO2. Every minute, O2 con-
sumption (V
·O2) and CO2 production (V
·CO2) rates are calcu-
lated using an algorithm for improved transient response [25].
Energy expenditure was calculated from V
·O2, V
·CO2, and uri-
nary nitrogen (N) excretion, as described previously [26]. Uri-
nary N was measured using the Kjeldahl method. Energy ex-
penditure and macronutrient oxidation were calculated from
the V
·O2, V
·CO2, and urinary N excretion. e rate of urinary
4 Sleep Med Res
Body Pillow Use and Sleeping Posture
Sleep Med Res 2021 Jun 2 [Epub ahead of print]
N excretion, an index of protein catabolism, was assumed to be
constant during the calorimetry [27].
Statistical Analysis
Physical characteristics of the participants, sleep parameters,
OSA-MA parameters, and body position are expressed as the
mean (SD). Paired t-tests were used to compare the sleep param-
eters and OSA-MA parameters between the mean values of the
trials. Time in each body position and longest duration of sus-
tained lateral time were assessed by 1-way repeated-measures
analysis of variance (ANOVA) and Bonferroni’s correction for
multiple comparisons. e SWS episode frequency was assessed
by 2-way repeated-measures ANOVA and Bonferroni’s correc-
tion for multiple comparisons. Data analysis was conducted us-
ing SPSS ver. 22 (IBM Corp., Armonk, NY, USA). A p value <
0.05 was considered statistically signicant.
RESULTS
Subjects Characteristics
The mean ± SD age, BMI, and MEQ score of the partici-
pants was 24.3 ± 7.8 years, 21.4 ± 1.7 kg/m2, and 51.1 ± 7.2, re-
spectively. All participants fullled all inclusion/exclusion cri-
teria and completed the 2 trials.
Body pressure distribution
In experiment 1, body pillow use signicantly reduced the mean
body pressure on the shoulder, hip, and whole body (Table 1).
Objective sleep quality
In experiment 2, the basic sleep architecture did not dier be-
tween the 2 trials in any of the sleep parameters (i.e., durations
of stage 1, 2, SWS, REM, and wakefulness aer sleep onset) (Ta-
ble 2). AHI and ODI were also not signicantly dierent between
the 2 experimental conditions. A 2-way ANOVA for the distri-
bution of the SWS episode duration showed signicant main ef-
fects of body pillow use [F(1, 9) = 1.609, p = 0.24] and SWS ep-
isode duration [F(9, 81) = 35.2, p < 0.001], as well as a signicant
interaction of the body pillow × SWS episode duration [F(9, 81)
= 2.5, p < 0.05]. Post-hoc analysis showed a signicant decrease
in the number of SWS episodes lasting only 30 s in the body pil-
low trial (p < 0.001) (Fig. 2). us, body pillow use improved deep
sleep maintenance without disturbing the sleep architecture.
Changed sleep body position
e mean time spent in the supine, lateral, and prone body
positions did not dier signicantly between the 2 trials (Fig. 3).
e longest sustained duration of the lateral body position was
signicantly extended with body pillow use compared with the
control trial [45.10 (7.05) vs. 70.05 (6.96) min for control and
body pillow trials, p < 0.05] (Fig. 4). us, body pillow use did
not increase the total amount of time in the lateral body posi-
tion, but did prolong the sustained duration of lateral body po-
sition during sleep.
Subjective sleep quality
None of the parameters (‘sleepiness on rising,’ ‘initiation and
maintenance of sleep,’ ‘sleep length,’ ‘refreshness,’ and ‘frequent
dreaming or nightmares’) of subjective sleep quality assessed by
the OSA-MA questionnaire diered signicantly between the
Table 1. Mean body pressure in each body part
Parameters Control Body pillow p-value
Shoulder (mm Hg) 33.1 ± 5.1 28.2 ± 4.0 < 0.01
Hip (mm Hg) 41.4 ± 8.6 31.5 ± 5.9 < 0.01
Whole body mean (mm Hg) 13.0 ± 0.7 11.5 ± 1.1 < 0.01
Values are mean ± SD for control and body pillow trials.
Table 2. Sleep architecture
Parameters Control Body pillow p-value
Total bedtime (min) 480.0 480.0
Total sleep time (min) 442.7 ± 41.9 449.4 ± 18.2 0.45
Wakefulness (min) 31.7 ± 41.4 24.8 ± 14.1 0.51
Sleep latency (min) 5.7 ± 3.1 5.5 ± 5.1 0.92
Sleep eciency (%) 93.3 ± 8.7 94.8 ± 3.0 0.50
Stage 1 (min) 46.0 ± 34.4 41.8 ± 19.0 0.51
Stage 2 (min) 231.7 ± 49.1 223.9 ± 43.4 0.57
SWS (min) 89.7 ± 33.1 100.0 ± 43.8 0.26
REM sleep (min) 75.3 ± 23.8 83.8 ± 21.6 0.20
REM sleep latency (min) 23.8 ± 15.3 20.8 ± 8.6 0.11
Arousal index (/night) 168.1 ± 90.4 154.2 ± 59.8 0.29
AHI (/h) 2.3 ± 1.7 2.3 ± 1.5 0.91
3%ODI 2.6 ± 1.6 2.2 ± 1.6 0.57
Values are mean ± SD for control and body pillow trials.
SWS: slow wave sleep, REM: rapid eye movement, AHI: apnea-hy-
popnea index, 3%ODI: 3% oxygen desaturation index.
30
25
20
15
10
5
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Number of SWS episode
Episode duration (min)
Control
With body pillow
Fig. 2. Frequency of slow wave sleep (SWS) episodes lasting
less than 5 min. *p < 0.05.
*
Park I, et al.
www.sleepmedres.org 5
control and body pillow trials (Table 3). erefore, the body pil-
low did not aect the subjective assessment of the quality of sleep.
Metabolic data
Energy expenditure [control trial: 381.99 (0.17) kcal/8 h vs.
body pillow trial: 378.81 (0.17) kcal/8 h, p = 0.55] and respira-
tory quotient [control trial: 0.84 (0.06) kcal/8 h vs. body pillow
trial: 0.85 (0.06) kcal/8 h, p = 0.47) during sleep diered between
the 2 trials.
DISCUSSION
One of the most common and eective treatments for sleep
apnea is CPAP [4]. In a previous study, the eects of positional
therapy were equivalent to that of CPAP for normalizing AHI,
sleep quality, and nocturnal oxygenation in patients with POSA
[20]. Positional therapies are associated with side eects, how-
ever, leading to low compliance. In contrast, a mild intervention,
such as body pillow use, may be free from side eects and be-
come a habitual daily routine. e present study investigated the
eect of body pillow use on sleeping body position and sleep ar-
chitecture in healthy young subjects, as assessed by a sleep ques-
tionnaire, sleep staging, and body position monitoring. Our nd-
ings revealed a positive eect of body pillow use to extend the
duration of a sustained lateral sleeping position and suppress
fragmented SWS without interfering with the subjective sleep
quality.
e frequency and severity of apnea/hypopnea events are in-
creased in the supine body position compared with the lateral
body position [28]. erefore, maintaining a lateral body posi-
tion during sleep might improve sleep apnea and the quality of
natural sleep. Positional therapy using the tennis ball technique
(a tennis ball is fastened to the back to discourage the patient from
sleeping supine) improved subjective sleep quality and daytime
alertness and decreased snoring loudness. Discomfort related to
the technique, however, led to its discontinuation in 38% of the
participants [28]. In another study, 80% of subjects stopped us-
ing the tennis ball technique, claiming that it was uncomfortable
[18]. As an alternative approach to avoid the supine position, pre-
vious studies designed special mattresses and pillows to facilitate
prone positioning, which improved the mean AHI and ODI, and
decreased the time spent in the supine position of OSA patients
without disruption of the sleep architecture judged by the PSG
recording system [29,30]. e special mattresses and pillows were
so eective that some subjects remained in the prone position
for the entire sleeping period, i.e., no changes in sleeping posi-
tion. Given the positive physiologic roles of changing the sleep-
ing position [31-33], it is better for patients with POSA to avoid
100
80
60
40
20
0
Supine Lateral Prone
%
Control
With body pillow
Fig. 3. Percent time in each body position between control and
body pillow trials. Values are mean ± SD for control and body pil-
low trials, and values from individual participants are also plotted.
SD: standard deviation.
Control
Body pillow use
Table 3. Subjective sleep quality assessed by the OSA sleep in-
ventory MA version
Parameters Control Body pillow p-value
Sleepiness on rising 48.7 ± 7.7 50.0 ± 8.8 0.65
Sleep duration 45.8 ± 12.0 48.3 ± 8.2 0.42
Initiation and maintenance
of sleep
42.4 ± 11.4 42.8 ± 10.3 0.94
Refreshness 49.4 ± 6.6 47.8 ± 8.8 0.71
Frequent dreaming, nightmares 45.2 ± 9.1 43.6 ± 11.4 0.30
Values are mean ± SD for control and body pillow trials.
OSA: e Oguri Shirakawa and Azumi standard rating scale, MA:
middle age and aged version.
120
100
80
60
40
20
0
Control Body pillow use
Min
Fig. 4. Longest sustained duration of lateral body position. Values
are mean ± SD for control and body pillow trials, and values for
individual participants are also plotted. *p < 0.05. SD: standard
deviation.
*
6 Sleep Med Res
Body Pillow Use and Sleeping Posture
Sleep Med Res 2021 Jun 2 [Epub ahead of print]
the supine position while not suppressing natural changes in
the sleeping body position. As a less stringent intervention, use
of a body pillow signicantly increased the duration of sustained
lateral body position while also allowing for changes in sleeping
positions. e use of a body pillow improved the body pressure
distribution and induced positive changes in sleeping body po-
sitions and sleep architecture without restricting changes in sleep-
ing body positions.
In the present study, we found that body pillow use did not sta-
tistically change objective and subjective sleep parameters com-
pared with the control trial. e absence of changes in the PSG
parameters between the 2 trials might be due to the nature of the
participants in this study. e participants were healthy young
adults with no sleep problems such as sleep apnea. e short sleep
latency, high sleep eciency, and long SWS duration of the par-
ticipants in the control trial may have resulted in a ceiling eect
that masked the eect of body pillow use on sleep parameters.
e number of short SWS episodes ranging from 0.55 min was
decreased by body pillow use, although there was no dierence
in the total duration of SWS between the 2 trials. Dierences in
the number of short SWS episodes were also observed when the
eects of 2 mattress types on sleep were assessed [21]. Although,
the mechanism responsible for the suppression of SWS episode
fragmentation by body pillow use remains to be elucidated, anal-
ysis of the continuity of SWS episodes may provide greater in-
sight into the quality of sleep.
In a previous study, a specially designed body pillow was used
to enforce the lateral position and facilitate the prone position,
which was rare in natural sleep in the present study [29,30]. e
prone position during sleep increases the heart rate and respira-
tory quotient compared with the supine position [34] and com-
promises thermoregulation in infants [35]. On the other hand,
it is speculated that a non-prone sleeping posture requires more
energy expenditure due to the respiratory movements of the rib
cage against gravity [36]. To assess the reasonable assumption
that dierence in the sleeping posture might induce changes in
energy metabolism, indirect calorimetry was performed using
a whole room metabolic chamber in the present study. Despite
the high time resolution of the indirect calorimetry in the pres-
ent study, there was no dierence in energy expenditure between
the 2 trials. According to these results, the lateral sleeping posi-
tion might not only positively inuence POSA, but might also
suppress SWS episode fragmentation.
e present study had some limitations. First, participants were
healthy young adults with no sleep problems such as sleep ap-
nea. us, further studies to evaluate the ecacy of body pillow
use for maintaining a desirable sleep posture should be performed
in participants with OSA, particularly POSA. Second, a previous
study revealed that prone positions were less likely in older per-
sons, who demonstrate a progressive preference for lateral po-
sitions due to a decline in spinal exibility and/or the extra eort
required for breathing [37]. ird, by the nature of the interven-
tion, this study design was not double-blinded, and placebo ef-
fect of pillow use on subjective sleep quality could not be exclud-
ed. ese limitations will be addressed in a future study.
In conclusion, the ndings of the present study demonstrate
that sleeping with a body pillow eectively extends the duration
of a sustained lateral sleeping position and prevents segmenta-
tion of SWS episodes.
Acknowledgments
e present study was nancially supported by Nishikawa Co., Ltd. e au-
thors would like to thank Takuto Nonomura, Yoji Shimura, and Saki Shi-
mada of Nishikawa Co., Ltd. for their important contributions to the devel-
opment of the body pillow.
Nishikawa Co., Ltd. and Japan Society for the Promotion of Science (Grant-
in-Aid for Scientic Research (B) 20H04120).
Conflicts of Interest
is study was nancially supported by Nishikawa Co., Ltd. MS has occa-
sionally given lectures on sleep physiology and hygiene at educational semi-
nars supported by Nishikawa Co., Ltd.
Authors’ Contribution
Conceptualization: Park IS, Kokubo T, Kawana F, Yanagisawa M, Satoh
M. Data curation: Park IS, Suzuki C, Yajima K. Formal analysis: Suzuki Y.
Funding acquisition: Kokubo T, Yanagisawa M. Project administration:
Fukusumi S. Writing—original dra: Park IS, Tokuyama K. Writing—re-
view & editing: Satoh M.
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