This preliminary study examined whether sleepwear affected sleep parameters using nocturnal polysomnography (nPSG) and self-reported questionnaire in healthy adults.
Fourteen participants were recruited (nine females and five males; mean age, 29.43±8.58 years). nPSG was conducted for three consecutive nights, including the adaptation night, and self-reported questionnaires about sleepwear and sleep parameters were completed. On the second and third nights after the adaption night, participants were randomly assigned to a group wearing the DPV576 experimental sleepwear (ES) on the first night with the control sleepwear (CS) worn the following night, or a group wearing the two types of sleepwear in the reverse order. The objective and subjective sleep parameters for each night were compared using the paired t-test.
Objective sleep variables were not significantly different between the two types of sleepwear. However, total sleep time (TST) on nPSG tended to be higher when participants wore the ES than the CS (p=0.06) in the results of nine who reported relatively high sleep quality (Pittsburgh Sleep Quality Index <5). When wearing the ES all participants reported more frequent dream (p=0.03), and less discomfort caused by sleepwear while lying down and moving in bed (i.e., tossing and turning), than the CS (p=0.04).
These results suggest that sleepwear type might affect objective sleep parameters (e.g., TST on nPSG) and be associated with changes in subjective sleep measures, such as the frequency of dreams and the discomfort caused by tossing and turning.
Sleep plays an important role in human health. It has been demonstrated that insufficient sleep and poor sleep quality are associated with physical, physiological, and psychological impairments [
Sleepwear improves the quality of sleep by preventing the body temperature from dropping sharply [
DPV576 is a mixture of nanodiamond and nanoplatinum solutions that improves immunity and reduces physical fatigue [
Few studies have explored whether there are differences in objective and subjective sleep parameters between functional and standard sleepwear. In this study, an experiment was conducted comparing DPV576 functional sleepwear (experimental sleepwear; ES) and similarly manufactured normal sleepwear (control sleepwear; CS). It was hypothesized that the type of sleepwear would influence objective and subjective sleep parameters.
Nine females and five males (mean age, 29.43±8.58 years) were recruited through an advertisement. The exclusion criteria were as follows: 1) females who were pregnant/nursing; 2) a history of serious medical problems; 3) currently taking medications that act on the nervous system, including sleeping pills; 4) DSM-5-based psychiatric diagnosis [
All participants completed self-reported questionnaires to obtain demographic and sleep-related information, as well as medical, psychiatric, neurological, and family histories. The self-reported questionnaires included the Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Dysfunctional Beliefs and Attitudes about Sleep (DBAS), International Restless Legs Syndrome Study Group Severity Scale (IRLSSG), Morningness-Eveningness Questionnaire (MEQ), and the Berlin Questionnaire (BQ).
The PSQI has a total of 19 items, and scores range from 0 to 21 points; higher scores indicate poorer subjective sleep quality [
In the morning following the each night of nocturnal polysomnography (nPSG), participants completed a survey on subjective sleep quality and their opinion of the sleepwear. They indicated how long it took to fall asleep [sleep latency (SL)], how long they slept for [total sleep time (TST)] in minutes, and the total number of awakenings. Sleep quality was scored from 1 (very tired and sleepy) to 4 points (refreshed).
In addition, participants indicated how deep their sleep was, how long they slept for, how often they woke, how many dreams they had, and how comfortable their sleep was, on a 7-point Likert scale (1: slept very lightly/slept very little/woke up very often/did not dream/very uncomfortable, respectively; 7: slept very deeply/slept for a very long time/did not wake up/had many dreams/very comfortable, respectively). They also scored their overall sleep satisfaction (1 point, very satisfied; 5 points, very dissatisfied) and indicated the reasons for satisfaction/dissatisfaction. The participants also indicated how uncomfortable they were due to the sleepwear, whether they experienced tension and stiffness, the level of discomfort felt in the neck, waist, and back, and the extent of discomfort caused by sleepwear while lying down and moving in bed (i.e., tossing and turning) (1 point, very comfortable; 4 points, very uncomfortable). Finally, they rated the sleepwear in terms of the material, size, tactile sensation, and overall satisfaction (1 point, very satisfied; 5 points, very dissatisfied). The evaluators did not interact with the participants when they were completing the questionnaire.
All participants underwent nPSG for three consecutive nights (adaptation night followed by two nPSG sessions to prevent the first night effect) [
ProFusion EEG software (ver. 3.4; Compumedics Ltd., Melbourne, Australia) was used for the nPSG recordings. The electrodes and sensors were attached to the participants in a standard manner. Electroencephalogram, electrooculogram, chin electromyogram, electrocardiogram, snoring sounds, oral and nasal airflow, chest movement, abdominal movement, limb movement, body position, and arterial oxygen saturation were continuously recorded during nighttime sleep. The PSG results were scored based on American Academy of Sleep Medicine (AASM) criteria [
The ES and CS were identical so that participants could not identify them (gray short-sleeved tops and long gray pants). The order of wear was randomized. All clothes were supplied by Venex Co., Ltd. (Atsugi, Japan).
Data were analyzed using SPSS software (ver. 25.0; IBM Corp., Armonk, NY, USA). The paired t-test was performed to compare objective and subjective sleep parameters between the CS and ES. Any effect of adaptation was evaluated by comparing the data between the second and third nights. Groups distinguished based on a PSQI cutoff score of 5 were also compared, to explore whether the results differed according to subjective sleep quality. A p-value <0.05 was considered significant.
The demographic and baseline characteristics of all participants are summarized in
The objective sleep variables did not differ significantly between the two sleepwear (
Participants reported dreaming more frequently (ES, 5.00±1.84; CS, 3.39±1.42; p=0.03), and less discomfort due to tossing and turning (ES, 3.43±0.76; CS, 3.71±0.47; p=0.04) when wearing the ES compared to the CS. No difference was seen in any other variable by sleepwear (
The nine participants with a PSQI <5 had more dreams when wearing the ES compared to the CS (ES, 5.39±1.52; CS, 3.50±1.52; p=0.01) (
Regardless of the type of sleepwear, N2 (%) stage sleep increased significantly on the third night (second night, 49.18±8.91%; third night, 56.13±7.93%; p=0.01), while for N3 (%) the opposite pattern was seen (second night, 16.60±3.97%; third night, 10.68±5.10%; p<0.001). Participants reported to sleep more comfortably during the third night than the second night (second night, 3.82±1.54; third night, 4.61±1.11; p=0.02).
In this study, we examined whether sleepwear affected sleep parameters (nPSG and self-reported questionnaire measures). None of the objective sleep variables were significantly different between the two types of sleepwear. However, nine participants who reported relatively high sleep quality (PSQI<5) showed a tendency toward increased TST when wearing the ES compared to the CS. This might be explained by the ES providing a more comfortable and relaxing sleep environment. These results suggested that the ES would be more effective for individuals among the general population who sleep relatively well. A more structured study design and larger number of samples will be needed to verify the effects of the DPV576 sleepwear on objective sleep quality.
N3 (%) stage sleep tended to increase when wearing the ES, but the difference was not significant. An increase of N3 (%) indicates deeper sleep, i.e., better sleep quality. Similar to this study, Shin et al. [
When wearing the ES, participants reported significantly more dreams than the CS. We were unable to determine the reason for this finding. Participants with the ES also reported less discomfort due to tossing and turning than those with the CS. Even considering the ceiling effect seen for the questionnaire scores, it seems that the ES was more comfortable than the CS during movement.
Although the mechanism of effect of the ES on sleep parameters is not clear yet, prior researchers assumed that DPV576 functional sleepwear seems to be benefit through the following results. According to a study, DPV576 might contribute to activate keratinocytes via multiple signal pathways, such as TRPV4 receptors which are one of the transient receptor potential channels and associated with inflammation and pain, while reducing stress [
N2 (%) increased, and N3 (%) decreased significantly, during the third night compared to the second night. However, it was difficult to analyze the relative proportions of the sleep stages based on only 2 nights of nPSG data. Moreover, the results differed between the subjective and objective measures. The more comfortable sleep reported during the third versus second night indicates that participants gradually adapted to the test environment during the experiment. Future studies should validate these results in the same experimental environment.
Some limitations of this study should be discussed. First, the statistical power may have been limited by the small sample size. Second, only healthy adults who slept relatively well participated in this study. Third, there was only one night of nPSG each while wearing the ES and CS, which is insufficient to fully understand the trends in the results. Therefore, future studies should include larger samples, more than two nights of nPSG with each type of sleepwear, and insomnia patients (for generalizability of the effects of sleepwear).
Despite these limitations, this study was significant in that it assessed sleep quality while wearing two different types of sleepwear, based on both objective and subjective measurements. We demonstrated the importance of the sleep environment, including the effect of DPV576 functional sleepwear, especially to subjective sleep quality. The results suggested that objective and subjective sleep parameters vary depending on the type of sleepwear.
This research was supported by Venex Co., Ltd.
The authors have no potential conflicts of interest to disclose.
Conceptualization: Yu Jin Lee. Data curation: Ha Young Lee, Mi hyun Lee. Formal analysis: Ha Young Lee. Funding acquisition: Yu Jin Lee. Investigation: Ha Young Lee, Jeong Eun Jeon. Methodology: Yu Jin Lee. Supervision: Kyung Hwa Lee, Yu Jin Lee. Writing—original draft: Ha Young Lee. Writing—review & editing: Ha Young Lee, Mi hyun Lee, Yu Jin Lee.
Demographic and baseline clinical characteristics of the participants
Variables | All (n=14) |
---|---|
Demographic | |
Age (yr) | 29.43±8.58 |
Sex (M:F) | 5:9 |
Self-reported questionnaire | |
PSQI | 4.43±2.95 |
ESS | 7.00±3.40 |
BDI | 4.71±4.12 |
BAI | 4.57±3.69 |
DBAS | 117.43±45.50 |
IRLSSG | 0.54±1.94 |
MEQ | 31.29±3.81 |
Data are presented as mean±standard deviation. PSQI: Pittsburgh Sleep Quality Index, ESS: Epworth Sleepiness Scale, BDI: Beck Depression Inventory, BAI: Beck Anxiety Inventory, DBAS: Dysfunctional Beliefs and Attitudes about Sleep, IRLSSG: International Restless Legs Syndrome Study Group Severity Scale, MEQ: Morningness-Eveningness Questionnaire
Polysomnographic and subjective sleep variables of all participants: comparison between ES and CS (n=14)
Variables | ES | CS | Differences | 95% CI | p-value |
---|---|---|---|---|---|
Polysomnography TRT (min) | 467.96±33.61 | 455.46±27.90 | 12.50±37.19 | -8.98–33.98 | 0.23 |
TST (min) | 432.21±46.46 | 425.50±38.34 | 6.71±37.42 | -14.89–28.32 | 0.51 |
SE (%) | 92.41±7.48 | 93.34±3.90 | -0.93±5.16 | -3.91–2.05 | 0.51 |
WASO (min) | 23.68±30.50 | 17.50±12.10 | 6.18±22.28 | -6.69–19.04 | 0.32 |
SL (min) | 11.36±11.79 | 11.11±8.30 | 0.25±10.88 | -6.03–6.53 | 0.93 |
% stage N1 | 9.63±5.02 | 9.73±6.23 | -0.10±4.77 | -2.86–2.66 | 0.94 |
% stage N2 | 52.56±8.15 | 52.31±10.09 | 0.24±11.45 | -6.37–6.85 | 0.94 |
% stage N3 | 14.51±5.82 | 12.76±5.02 | 1.75±8.49 | -3.15–6.65 | 0.45 |
% stage REM | 23.29±4.13 | 25.19±4.71 | -1.91±4.01 | -4.22–0.41 | 0.10 |
AHI (/h) | 3.40±6.31 | 3.79±5.53 | -0.39±1.82 | -1.44–0.67 | 0.44 |
Average O2 (%) | 96.36±0.93 | 96.29±0.99 | 0.07±0.83 | -0.41–0.55 | 0.75 |
Minimum O2 (%) | 91.29±3.71 | 90.86±4.09 | 0.43±3.01 | -1.31–2.16 | 0.60 |
PLMSI (/h) | 0.61±2.05 | 2.82±5.87 | -2.21±5.36 | -5.30–0.89 | 0.15 |
Self-reported questionnaire | |||||
SL (min) | 22.00±21.68 | 20.93±14.75 | 1.07±21.85 | -11.55–13.69 | 0.86 |
TST (min) | 437.86±52.50 | 426.43±47.49 | 11.43±47.37 | -15.92–38.78 | 0.38 |
Number of awakenings | 3.50±1.64 | 3.14±2.21 | 0.36±2.03 | -0.82–1.53 | 0.52 |
Score on feeling refreshed after sleep | 2.79±0.97 | 2.86±0.86 | -0.07±1.07 | -0.69–0.55 | 0.81 |
Scores on sleep quality | |||||
Deep sleep | 4.21±1.83 | 4.82±1.41 | -0.61±1.78 | -1.63–0.42 | 0.22 |
Amount of sleep | 4.57±1.28 | 4.79±1.05 | -0.21±1.12 | -0.86–0.43 | 0.49 |
FOA | 3.39±1.44 | 4.07±1.33 | -0.68±1.84 | -1.74–0.38 | 0.19 |
FOD | 5.00±1.84 | 3.39±1.42 | 1.61±2.40 | 0.22–2.99 | 0.03 |
Comfortable | 4.11±1.18 | 4.32±1.59 | -0.21±1.31 | -0.97–0.54 | 0.55 |
Overall sleep satisfaction | 2.64±1.15 | 2.57±0.94 | 0.07±1.00 | -0.50–0.65 | 0.79 |
Scores on sleepwear | |||||
Comfort | 3.71±0.61 | 4.00±0.00 | -0.29±0.61 | -0.64–0.07 | 0.10 |
Relax | 3.86±0.36 | 4.00±0.00 | -0.14±0.36 | -0.35–0.07 | 0.16 |
Comfort in neck | 4.00±0.00 | 4.00±0.00 | - | - | - |
Comfort in waist | 4.00±0.00 | 3.86±0.36 | 0.14±0.36 | -0.07–0.35 | 0.16 |
Comfort in back | 3.93±0.27 | 4.00±0.00 | -0.07±0.27 | -0.23–0.08 | 0.34 |
Tossing and turning | 3.43±0.76 | 3.71±0.47 | -0.29±0.47 | -0.56 to -0.02 | 0.04 |
Satisfaction with material | 1.79±0.97 | 1.64±0.74 | 0.14±0.86 | -0.36–0.64 | 0.55 |
Satisfaction with size | 2.14±0.86 | 2.07±1.00 | 0.07±0.62 | -0.28–0.43 | 0.67 |
Satisfaction with tactile sensation | 1.79±0.89 | 1.50±0.65 | 0.29±0.83 | -0.19–0.76 | 0.22 |
Overall satisfaction | 1.93±0.83 | 1.86±0.66 | 0.07±0.73 | -0.35–0.49 | 0.72 |
p<0.05.
Data are presented as mean±standard deviation. ES: experimental sleepwear, CS: control sleepwear, TRT: total recording time, TST: total sleep time, SE: sleep efficiency, WASO: wake after sleep onset time, SL: sleep latency, REM: rapid eye movement, AHI: apnea-hypopnea index, PLMI: periodic limb movement index, FOA: frequency of awakenings, FOD: frequency of dreams, CI: confidence interval
Polysomnographic and subjective sleep variables of participants with low PSQI scores (<5): comparison between ES and CS (n=9)
Variables | ES | CS | Differences | 95% CI | p-value |
---|---|---|---|---|---|
Polysomnography | |||||
TRT (min) | 471.94±36.84 | 457.33±23.49 | 14.61±21.21 | -1.70–30.92 | 0.07 |
TST (min) | 447.44±37.31 | 433.61±28.39 | 13.83±19.38 | -1.07–28.73 | 0.06 |
SE (%) | 94.86±3.96 | 94.86±2.58 | 0.00±3.35 | -2.57–2.57 | 1.00 |
WASO (min) | 13.22±13.87 | 11.94±8.21 | 1.28±11.38 | -7.47–10.03 | 0.74 |
SL (min) | 10.67±12.34 | 10.33±9.00 | 0.33±10.98 | -8.10–8.77 | 0.93 |
% stage N1 | 8.22±3.93 | 7.34±3.15 | 0.88±2.18 | -0.80–2.55 | 0.26 |
% stage N2 | 54.41±7.17 | 53.13±9.88 | 1.28±10.11 | -6.50–9.05 | 0.71 |
% stage N3 | 13.32±6.21 | 13.21±4.73 | 0.11±7.42 | -5.59–5.81 | 0.97 |
% stage REM | 24.02±4.70 | 26.31±5.15 | -2.29±3.50 | -4.98–0.40 | 0.09 |
AHI (/h) | 0.96±1.23 | 1.73±2.08 | -0.78±1.47 | -1.90–0.35 | 0.15 |
Average O2 (%) | 96.67±0.71 | 96.44±0.73 | 0.22±0.97 | -0.52–0.97 | 0.51 |
Minimum O2 (%) | 93.00±2.18 | 92.89±2.20 | 0.11±3.33 | -2.45–2.67 | 0.92 |
PLMSI (/h) | 0.10±0.30 | 2.78±6.60 | -2.68±6.65 | -7.79–2.43 | 0.26 |
Self-reported questionnaire | |||||
SL (min) | 17.22±9.39 | 17.78±10.03 | -0.56±14.24 | -11.50–10.39 | 0.91 |
TST (min) | 447.78±38.33 | 426.67±47.17 | 21.11±31.80 | -3.33–45.55 | 0.08 |
Number of awakenings | 3.44±1.72 | 3.11±2.76 | 0.33±2.14 | -1.31–1.98 | 0.65 |
Score on feeling refreshed after sleep | 2.78±0.97 | 2.78±0.97 | 0.00±1.00 | -0.77–0.77 | 1.00 |
Scores on sleep quality | |||||
Deep sleep | 4.06±1.72 | 4.72±1.23 | -0.67±2.00 | -2.20–0.87 | 0.35 |
Amount of sleep | 4.28±0.87 | 4.39±0.82 | -0.11±0.93 | -0.82–0.60 | 0.73 |
FOA | 2.94±1.31 | 3.83±1.48 | -0.89±2.03 | -2.45–0.67 | 0.22 |
FOD | 5.39±1.52 | 3.50±1.52 | 1.89±1.76 | 0.53–3.24 | 0.01 |
Comfortable | 4.17±1.09 | 4.28±1.46 | -0.11±1.05 | -0.92–0.70 | 0.76 |
Overall sleep satisfaction | 2.78±1.2 | 2.67±0.87 | 0.11±0.93 | -0.60–0.82 | 0.73 |
Scores on sleepwear | |||||
Comfort | 3.78±0.67 | 4.00±0.00 | -0.22±0.67 | -0.73–0.29 | 0.35 |
Relax | 3.89±0.33 | 4.00±0.00 | -0.11±0.33 | -0.37–0.15 | 0.35 |
Comfort in neck | 4.00±0.00 | 4.00±0.00 | - | - | - |
Comfort in waist | 4.00±0.00 | 3.78±0.44 | 0.22±0.44 | -0.12–0.56 | 0.17 |
Comfort in back | 4.00±0.00 | 4.00±0.00 | - | - | - |
Tossing and turning | 3.44±0.73 | 3.78±0.44 | -0.33±0.50 | -0.72–0.05 | 0.08 |
Satisfaction with material | 1.78±0.97 | 1.78±0.83 | 0.00±0.71 | -0.54–0.54 | 1.00 |
Satisfaction with size | 2.00±1.00 | 2.00±1.22 | 0.00±0.50 | -0.38–0.38 | 1.00 |
Satisfaction with tactile sensation | 1.89±0.93 | 1.56±0.73 | 0.33±0.87 | -0.33–1.00 | 0.28 |
Overall satisfaction | 2.00±0.87 | 2.00±0.71 | 0.00±0.50 | -0.38–0.38 | 1.00 |
p<0.05.
Data are presented mean±standard deviation. ES: experimental sleepwear, CS: control sleepwear, TRT: total recording time, TST: total sleep time, SE: sleep efficiency, WASO: wake after sleep onset time, SL: sleep latency, REM: rapid eye movement, AHI: apnea-hypopnea index, PLMI: periodic limb movement index, FOA: frequency of awakenings, FOD: frequency of dreams, CI: confidence interval