Gender Differences in Polysomnographic Sleep in Young Healthy Sleepers

Abstract

Middle-aged and elderly populations exhibit gender differences in polysomnographic (PSG) sleep; however, whether young men and women also show such differences remains unclear. Thirty-one young healthy sleepers (16 men and 15 women, aged 18 to 30 yr, mean+/-SD, 20.5+/-2.4 yr) completed 3 consecutive overnight sessions in a sleep laboratory, after maintaining a stable sleep-wake cycle for 1 wk before study entry. Standard PSG sleep and self-rated sleepiness data were collected each night. Across nights, women showed better sleep quality than men: they fell asleep faster (shorter sleep onset latency) and had better sleep efficiency, with more time asleep and less time awake (all differences showed large effect sizes, d=0.98 to 1.12). By contrast, men were sleepier than women across nights. Both men and women demonstrated poorer overall sleep quality on the first night compared with the subsequent 2 nights of study. We conclude young adult healthy sleepers show robust gender differences in PSG sleep, like older populations, with better sleep quality in women than in men. These results highlight the importance of gender in sleep and circadian rhythm research studies employing young subjects and have broader implications for women's health issues relating to these topics.

Full text

GENDER DIFFERENCES IN POLYSOMNOGRAPHIC SLEEP
IN YOUNG HEALTHY SLEEPERS
Namni Goel, Hyungsoo Kim, and Raymund P. Lao
Department of Psychology, Wesleyan University, Middletown, Connecticut, USA
Middle-aged and elderly populations exhibit gender differences in polysomnographic
(PSG) sleep; however, whether young men and women also show such differences
remains unclear. Thirty-one young healthy sleepers (16 men and 15 women, aged
18 to 30 yr, mean +SD, 20.5 +2.4 yr) completed 3 consecutive overnight sessions
in a sleep laboratory, after maintaining a stable sleep-wake cycle for 1 wk before
study entry. Standard PSG sleep and self-rated sleepiness data were collected each
night. Across nights, women showed better sleep quality than men: they fell asleep
faster (shorter sleep onset latency) and had better sleep efficiency, with more time
asleep and less time awake (all differences showed large effect sizes, d¼0.98 to
1.12). By contrast, men were sleepier than women across nights. Both men and
women demonstrated poorer overall sleep quality on the first night compared with
the subsequent 2 nights of study. We conclude young adult healthy sleepers show
robust gender differences in PSG sleep, like older populations, with better sleep
quality in women than in men. These results highlight the importance of gender in
sleep and circadian rhythm research studies employing young subjects and have
broader implications for women’s health issues relating to these topics.
Keywords Gender Differences, Polysomnography, Sleepiness, First Night Effect,
Objective Sleep, Subjective Sleep, Circadian Sleep-Wake Rhythm
INTRODUCTION
A number of gender differences exist in human circadian rhythms
(reviewed in Lee et al., 2004). However, whether young adults show
gender differences in the sleep-wake cycle—a fundamental circadian
rhythm that is, in part, controlled by the circadian clock—remains equi-
vocal. This topic has significance for various women’s health issues relating
to sleep and circadian rhythms (see Collop et al., 2004; Smolensky et al.,
2005).
Submitted May 9, 2005, Returned for revision June 25, 2005, Accepted July 19, 2005
Address correspondence to Namni Goel, PhD, Department of Psychology, 207 High Street, Judd
Hall, Wesleyan University, Middletown, CT 06459, USA. E-mail: ngoel@wesleyan.edu
Chronobiology International, 22(5): 905–915, (2005)
Copyright #2005 Taylor & Francis, Inc.
ISSN 0742-0528 print/1525-6073 online
DOI: 10.1080/07420520500263235
905

Middle-aged and elderly female populations report poorer subjective
sleep quality than men of similar age (Hayter, 1983; Hoch et al., 1988;
Li et al., 2002; Middelkoop et al., 1996; but see Voderholzer et al.,
2003). However, objective polysomnographic (PSG) measures in these
groups show the opposite pattern; women have better sleep quality than
men, including more slow-wave sleep (SWS), more rapid-eye movement
(REM) sleep, and fewer night-time awakenings (Fukuda et al., 1999;
Hume et al., 1998; Kobayashi et al., 1998; Rediehs et al., 1990; Reynolds
et al., 1985; Wauquier et al., 1992; Webb, 1982). Elderly women also
show longer REM latencies than elderly men (Hoch et al., 1988; Rediehs
et al., 1990).
Young women, like older women, consistently report poorer sleep
quality than men, including longer sleep onset latencies and more noctur-
nal awakenings ( Janson et al., 1995; Li et al., 2002; Lindberg et al., 1997;
Mniszek, 1988; Tsai and Li, 2004). Yet, only a few PSG studies have
detected gender differences in younger populations. For example,
Williams and colleagues (1974) found that women awaken less frequently
and have more stage 2 sleep than men. Women also have less SWS during
the second half of the night, with greater SWS decreases from the first to
the second half of the night (Antonijevic et al., 1999). Most studies,
however, have failed to find significant gender differences using PSG
(Armitage, 1995; Armitage et al., 2000; Carrier et al., 2001; Dijk et al.,
1989; Ehlers and Kupfer, 1997; Elsenbruch et al., 1999). In some cases,
these latter studies used only 1 non-adaptation night or did not impose a
stable sleep-wake cycle before laboratory data collection. Thus, we deter-
mined whether gender differences would emerge across 3 consecutive lab-
oratory nights in young adults who maintained a stable sleep-wake cycle
for 1 wk before study entry.
This experiment investigated gender differences in PSG sleep and self-
rated sleepiness in young male and female healthy sleepers. We hypothe-
sized that young women would show better PSG sleep quality than young
men across nights, as has been demonstrated for middle-aged and elderly
populations, but poorer subjective sleep (more sleepiness). We also pre-
dicted that all subjects would show first night effects, with poorer sleep
quality on the first laboratory night compared with the second and third
nights.
MATERIALS AND METHODS
Participants
This study used the same subjects as those described in more detail
in a companion paper in this journal issue (Goel et al., 2005). Briefly,
31 subjects, 16 men and 15 women, ages 18 to 30 yr (overall mean
N. Goel, H. Kim, and R. P. Lao906

age +SD, 20.5 +2.4 yr; men: 20.2 +2.9 yr; women: 20.8 +1.8 years)
participated. Subjects were recruited through local newspaper advertise-
ments and campus postings and were screened by telephone and in-
person interviews. These interviews ascertained that all subjects were in
good physical and psychological health, were healthy sleepers, and were
not using central nervous system medications. Subjects with extreme
morningness or eveningness, assessed by the Morningness-Eveningness
Questionnaire (Horne and O
¨stberg, 1976), were excluded.
Three women were taking oral contraceptives, and all women had
normal menstrual cycles. An equal number of women were in their
luteal (n¼6) or follicular (n¼6) menstrual cycle phases. Subjects main-
tained a stable wake-up time and bedtime, documented by sleep logs for
1 wk before study entry. Wesleyan University’s Institutional Review
Board approved the study, and all procedures conformed to the Declara-
tion of Helsinki and to the ethical and good practice standards for biologi-
cal rhythm research as advanced by the Journal (Touitou et al., 2004).
Subjects received monetary compensation for participation and signed
informed consent before study entry.
Polysomnographic Recordings
Central and occipital electroencephalographic (EEG), electrooculo-
graphic (EOG), and submental electromyographic (EMG) measures were
recorded from 24:00 (lights off) to 08:00 h (lights on). During the adap-
tation night, subjects were screened for sleep pathologies, including
apneas, oxygen desaturation, and periodic limb movements by monitoring
respiratory effort, nasal airflow, arterial oxygen saturation level, bilateral
anterior tibialis EMG, and heart rate (EKG). Sleep records were visually
scored in 30-sec epochs according to Rechtschaffen and Kales’ (1968) stan-
dard scoring criteria by two trained scorers blind to the experimental con-
ditions. Inter-rater reliability for the two scorers was 95.2%. Sleep
parameters for the whole night and for the first (24:00 to 04:00 h) and
second (04:00 to 08:00 h) half of each night were analyzed.
Subjective Sleepiness Questionnaire
The Stanford Sleepiness Scale (SSS; Hoddes et al., 1973) quantifies the
progressive, subjective stages of the sleep-alertness continuum, with a scale
from 1 to 7 (1: feeling active, vital, alert, or wide awake; 7: sleep onset soon;
lost struggle to remain awake). The SSS has been tested with repeated
acute sampling periods (e.g., 15 min).
Gender Differences in Polysomnographic Sleep 907

Procedure
This study used the same procedure described in more detail in a com-
panion manuscript in this journal issue (Goel et al., 2005). Briefly, subjects
slept in a sleep laboratory for 3 consecutive overnight sessions. Each
session lasted from approximately 21:00 to 08:00 h. On the second and
third intervening days, subjects left the laboratory between 08:00 to
21:00 h and engaged in their habitual activities. On these study days, sub-
jects refrained from napping and exercise, and from alcohol or caffeine
intake.
Electrode placement for PSG recordings occurred at 21:00 h on all
3 nights. Subjects then engaged in recreational activities until bedtime
(24:00 h) on the first night and until 23:10 h on the second and third
nights. PSG data were collected from 24:00 to 08:00 h each night. Subjects
remained in bed if they awakened before 08:00 h. The SSS was
administered at 23:50 and 08:00 h each night and morning, respectively.
This instrument is designed for repeated measures over short time inter-
vals, as noted above; moreover, any possible repeated administration
effects would be observed across all nights.
Statistical Analyses
Repeated measures analyses of variance, with gender and session
order as between-subject factors, examined differences in PSG sleep
measures and SSS scores across the 3 nights. Our companion manuscript
in this journal issue reports on the 2-night analyses comparing the effects
of lavender odor vs. a control (administered on the second and third
nights) on these and other measures (Goel et al., 2005). Post-hoc tests, cor-
rected for multiple comparisons, examined 2-night differences following
significant overall 3-night main effects. The magnitude of the between-
group differences in scores was expressed as effect size, d, the standardized
difference between means (d¼0.3, small; 0.5, medium; 0.8, large; Cohen,
1988). Data are presented as mean +SD; p,0.05 was considered signifi-
cant for all statistical analyses.
RESULTS
Polysomnographic (PSG) Sleep
First Night Effects
Table 1 illustrates whole night PSG sleep measures for the first night
(Night 1) and Nights 2 and 3 (combined). On the first night, all subjects
had less total sleep time (F
2,25
¼6.45, p,0.006, d¼0.64) and worse
sleep efficiency (F
2,25
¼5.95, p,0.008, d¼0.62) and sleep maintenance
N. Goel, H. Kim, and R. P. Lao908

efficiency (F
2,25
¼8.35, p,0.002, d¼0.75) compared with the other
2 nights. Moreover, subjects had more Stage 1 %SPT (sleep period time,
the duration from sleep onset to the end of sleep; F
2,25
¼26.57, p,
0.001, d¼0.96), total wake time (F
2,25
¼5.99, p,0.007, d¼0.62), and
wake after sleep onset (WASO) %SPT (F
2,25
¼8.11, p,0.002, d¼0.75).
They also showed less SWS %SPT (F
2,25
¼40.15, p,0.001, d¼0.51
and REM %SPT (F
2,25
¼5.32, p,0.02, d¼0.68). There were no
additional first night differences in sleep measures for the first or second
half of the night beyond those reported for the whole night.
Night Gender Differences
There were no significant night gender interactions across all
3 nights for any PSG measure.
Gender Differences
Table 2 describes whole night PSG sleep measures for men and women
across all 3 nights. Women showed significantly longer total sleep time
(F
1,26
¼6.10, p,0.02, d¼0.98) and SPT (F
1,26
¼8.01, p,0.009,
d¼1.11), and better sleep efficiency than men (F
1,26
¼5.82, p,0.02,
d¼0.96). Women also had significantly less total wake time
(F
1,26
¼6.03, p,0.02, d¼0.98). Moreover, sleep onset latency (the
TABLE 1 Mean +SD Whole Night Sleep Measures for the 3 Nights
PSG measure Night 1 Night 2 and 3
Total sleep time (TST), min
a
440.5 +36.2 458.8 +18.7
Sleep period time (SPT), min 455.2 +29.0 464.4 +14.3
Total wake time (TWT), min
a
36.6 +33.5 19.9 +18.4
Sleep efficiency (SE), %
a
92.3 +7.1 95.8 +3.8
Sleep maintenance efficiency (SME), %
a
96.7 +3.4 98.8 +2.0
Sleep onset latency (SOL), min 21.1 +24.5 14.2 +14.2
Wake after sleep onset (WASO), %SPT
a
3.3 +3.4 1.2 +2.0
WASO, latency, min 98.5 +101.2 198.3 +101.1
Stage 1, %SPT
a
5.7 +4.1 2.6 +2.2
Stage 1, latency, min 21.1 +24.5 19.7 +31.4
Stage 2, %SPT 66.8 +7.1 66.3 +5.3
Stage 2, latency, min 26.6 +24.3 18.4 +15.6
Slow-wave sleep (SWS; Stages 3 þ4), SPT
a
4.3 +4.1 6.3 +4.1
SWS (Stages 3 þ4), latency, min 36.8 +17.1 35.4 +17.0
Non-rapid eye movement (NREM), %SPT 76.6 +6.3 75.2 +4.8
Rapid-eye movement (REM), %SPT
a
19.9 +6.4 23.6 +4.3
REM, latency, min 124.6 +76.9 110.4 +45.4
a
p,0.05, post-hoc corrected comparisons for Night 1 vs. Nights 2 and 3 following significant 3-night
overall main effects.
Gender Differences in Polysomnographic Sleep 909

time it takes to initially fall asleep) was significantly shorter for women
(F
1,26
¼8.09, p,0.009, d¼1.11), as were latencies to stage 1
(F
1,26
¼8.22, p,0.008, d¼1.12) and stage 2 sleep (F
1,26
¼8.05,
p,0.009, d¼1.11). There were no additional gender differences in
sleep measures for the first or second half of the night, beyond those
reported for the whole night.
Subjective Sleepiness
Across all 3 nights, men were sleepier than women, as indicated by
significantly higher SSS scores (F
1,19
¼5.38, p,0.03, d¼0.89;
Figure 1). There were no other significant SSS differences.
DISCUSSION
This study found significant gender differences in PSG sleep—with
large effect sizes—across all 3 nights. A longer sleep period time, shorter
total time awake, better sleep efficiency, and shorter latencies to sleep
onset collectively demonstrate better sleep quality in women. Subjective
sleepiness across nights, however, was higher in men. All subjects also
showed first night effects, with poorer sleep quality on the first laboratory
night compared with the second and third nights.
Our gender difference data concur with those from middle-aged and
elderly populations (Fukuda et al., 1999; Hume et al., 1998; Kobayashi
TABLE 2 Mean +SD Whole Night Sleep Measures for Men and Women Across
the 3 Nights
PSG measure Men Women
TST, min
a
444.2 +23.4 463.1 +12.9
SPT, min
a
453.9 +17.4 469.4 +8.4
TWT, min
a
33.5 +22.8 15.8 +10.8
SE, % 93.0 +4.8 96.6 +2.3
SME, % 97.8 +2.5 98.6 +1.5
SOL, min
a
23.2 +16.3 9.3 +5.6
WASO, %SPT 2.2 +2.5 1.4 +1.5
WASO, latency, min 179.9 +69.6 99.7 +61.7
Stage 1, %SPT 3.7 +1.9 3.5 +3.5
Stage 1, latency, min
a
23.4 +16.3 9.3 +5.6
Stage 2, %SPT 66.6 +3.5 66.6 +7.1
Stage 2, latency, min
a
28.1 +16.5 13.7 +6.8
SWS (Stages 3 þ4), %SPT 5.5 +3.6 5.7 +4.6
SWS (Stages 3 þ4), latency, min 53.3 +18.4 42.7 +11.2
NREM, %SPT 75.8 +4.9 75.6 +4.5
REM, %SPT 22.0 +4.3 22.9 +4.0
REM, latency, min 122.6 +43.4 104.2 +48.8
a
Significant gender effect across all 3 nights (p,0.05).
N. Goel, H. Kim, and R. P. Lao910

et al., 1998; Rediehs et al., 1990; Reynolds et al., 1985; Wauquier et al.,
1992; Webb, 1982). However, they contrast with findings from a number
of studies that failed to detect gender differences in younger populations
using PSG (Armitage, 1995; Armitage et al., 2000; Carrier et al., 2001;
Dijk et al., 1989; Ehlers and Kupfer, 1997; Elsenbruch et al., 1999).
Notably, each of these latter studies detected gender differences, with
women showing greater delta power during NREM sleep, but only after
employing EEG spectral analysis, a more sensitive measure than PSG.
Thus, it is possible that underlying gender differences were amplified by
our laboratory’s environmental conditions, enabling detection by PSG
alone. Other factors such as the number of study nights, prior sleep
history, or recruitment of subjects also may underlie our positive findings.
The gender differences do not result from sleep deprivation incurred
from the adaptation night leading to better rebound sleep in women on the
second and third nights, since the differences persisted across all 3 nights.
The differences also are not due to prior sleep history in our subjects, since
both men and women maintained stable wake-up times and bedtimes
before entry. While 3 women in our study used oral contraceptives, statisti-
cal analyses excluding their data did not alter our results; thus, the
observed differences cannot be attributed to oral contraceptive use
(Burdick et al., 2002). Conceivably, the differences between men and
women could be due to the effects of cyclical levels of female reproductive
hormones (including estrogen, progesterone, and luteinizing hormone)
on sleep (Driver and Baker, 1998; Lee et al., 1990; Manber and Armitage,
FIGURE 1 Stanford Sleepiness Scale (SSS) scores across all 3 nights for men and women (mean +SD).
Significantly higher in men than in women, p,0.03.
Gender Differences in Polysomnographic Sleep 911

1999; Shaver, 2002). Since an equal number of women were in the luteal
(n¼6) or follicular (n¼6) menstrual cycle phases, however, this possi-
bility seems improbable. Overall, since our women were healthy and nor-
mally menstruating, their sleep unlikely was affected by menstrual phase
(Baker et al., 2001; Driver and Baker, 1998; Driver et al., 1996).
Although women showed better sleep across nights, men had higher
SSS scores, indicating greater sleepiness. Our results contrast with those
of previous studies documenting poorer self-reported sleep measures in
women compared with men (Janson et al., 1995; Li et al., 2002; Lindberg
et al., 1997; Mniszek, 1988; Tsai and Li, 2004). Our discrepant results may
be due to use of only one self-rated measure in our study: other measures,
such as estimations of sleep onset latency, number of awakenings, and total
time asleep and awake may have indicated perceptions of poorer sleep
quality in women.
Although men were sleepier, they showed longer sleep onsets; by
contrast, women, who were less sleepy, fell asleep faster. Thus, both
men and women showed discrepancies between subjective sleepiness
and objective sleep measures. Other laboratories also have reported
such inaccuracies in healthy, nondepressed sleepers for certain sleep
measures (Armitage et al., 1997; Baker et al., 1999; Frankel et al.,
1976; Shaver et al., 1991). Therefore, collection of both kinds of measures
is necessary for obtaining an accurate and complete assessment of sleep
quality in younger populations.
A number of sleep measures showed first-night effects. Our results cor-
roborate data from other laboratories using nondepressed subjects who
report lower sleep efficiency, increased wakefulness, less REM and
NREM sleep, and longer latencies to sleep onset and REM sleep on the
first night (Agnew et al., 1966; Curcio et al., 2004; Lorenzo and Barbanoj,
2002; Mendels and Hawkins, 1967; Schmidt and Kaelbling, 1971; Tamaki
et al., 2005; Toussaint et al., 1995; Webb and Campbell, 1979). However,
our data contrast with a few studies that failed to find multiple first-night
disruptive effects (Browman and Cartwright, 1980; Coble et al., 1974;
Kader and Griffin, 1983). Nights 2 and 3 did not differ in these measures,
supporting other studies that indicate the disruptive effects last only
1 night (Agnew et al., 1966; Lorenzo & Barbanoj, 2002; Webb and
Campbell, 1979). Notably, since PSG measures did not show significant
night gender interactions, women slept better even on Night 1,
although both genders fared better on Nights 2 and 3. Environmental
sleeping conditions, including restricted movements, the presence of elec-
trodes, technicians, and cameras, as well as increased arousal and vigilance
may underlie such first-night disruptions.
Morning subjective sleepiness ratings did not differ across the 3 nights,
despite PSG sleep differences. We assessed sleepiness immediately upon
awakening (within 1 to 2 min), a time when lingering sleepiness could be
N. Goel, H. Kim, and R. P. Lao912

due to sleep inertia (Tassi and Muzet, 2000). Thus, our study methodology
may have hampered detection of differences in morning sleepiness,
explaining why objective sleep differences on the first night were not
reflected in subjective sleepiness. Assessing sleepiness later after awaken-
ing (i.e., 15 min) may be a more accurate morning indicator of this
measure.
This study revealed robust gender differences in sleep measures across
3 nights. Young women showed better sleep quality overall: they had
shorter latencies to sleep onset, less total wake time, and better sleep effi-
ciency. By contrast, subjective sleepiness was higher in men across
nights. Thus, both men and women showed discrepancies between subjec-
tive and objective sleep measures. Our results emphasize the significance
of gender in sleep and circadian rhythm studies in young adults and
have important applications for medical issues relating to women in
these research areas.
ACKNOWLEDGMENTS
This research was supported by a grant from the Sense of Smell Insti-
tute (N.G.). R.P. Lao received summer support from a Howard Hughes
Medical Institute grant for undergraduate education at Wesleyan Univer-
sity. We thank Dave Bushnell, Glenda Etwaroo, Ying-Ju Lai, and Sonia
Vesely for assistance in data collection.
REFERENCES
Agnew, H.W., Jr., Webb, W.B., Williams, R.L. (1966). The first night effect: an EEG study of sleep.
Psychophysiology 2:263– 266.
Antonijevic, I.A., Murck, H., Frieboes, R., Holsboer, F., Steiger, A. (1999). On the gender differences in
sleep-endocrine regulation in young normal humans. Neuroendocrinology 70:280–287.
Armitage, R. (1995). The distribution of EEG frequencies in REM and NREM sleep stages in healthy
young adults. Sleep 18:334– 341.
Armitage, R., Trivedi, M., Hoffmann, R., Rush, A.J. (1997). Relationship between objective and subjec-
tive sleep measures in depressed patients and healthy controls. Depress. Anxiety 5:97 – 102.
Armitage, R., Hoffmann, R., Trivedi, M., Rush, A.J. (2000). Slow-wave activity in NREM sleep: sex and
age effects in depressed outpatients and healthy controls. Psychiatry Res. 95:201– 213.
Baker, F.C., Maloney, S., Driver, H.S. (1999). A comparison of subjective estimates of sleep with objec-
tive polysomnographic data in healthy men and women. J. Psychosom. Res. 47:335–341.
Baker, F.C., Waner, J.I., Vieira, E.F., Taylor, S.R., Driver, H.S., Mitchell, D. (2001). Sleep and 24 hour
body temperatures: a comparison in young men, naturally cycling women and women taking hor-
monal contraceptives. J. Physiol. 530:565– 574.
Browman, C.P., Cartwright, R.D. (1980). The first-night effect on sleep and dreams. Biol. Psychiatry
15:809– 812.
Burdick, R.S., Hoffmann, R., Armitage, R. (2002). Short note: oral contraceptives and sleep in
depressed and healthy women. Sleep 25:347–349.
Carrier, J., Land, S., Buysse, D.J., Kupfer, D.J., Monk, T.H. (2001). The effects of age and gender on
sleep EEG power spectral density in the middle years of life (ages 20– 60 years old). Psychophysio-
logy 38:232– 242.
Gender Differences in Polysomnographic Sleep 913

Coble, P., McPartland, R.J., Silva, W.J., Kupfer, D.J. (1974). Is there a first night effect? (a revisit). Biol.
Psychiatry 9:215– 219.
Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences, 2nd ed.. Hillsdale, NJ: Lawrence
Erlbaum Associates.
Collop, N.A., Adkins, D., Phillips, B.A. (2004). Gender differences in sleep and sleep-disordered
breathing. Clin. Chest Med. 25:257– 268.
Curcio, G., Ferrara, M., Piergianni, A., Fratello, F., De Gennaro, L. (2004). Paradoxes of the first-night
effect: a quantitative analysis of antero-posterior EEG topography. Clin. Neurophysiol.
115:1178– 1188.
Dijk, D.J., Beersma, D.G.M., Bloem, G.M. (1989). Sex differences in the sleep EEG of young adults:
visual scoring and spectral analysis. Sleep 12:500–507.
Driver, H.S., Baker, F.C. (1998). Menstrual factors in sleep. Sleep Med. Rev. 2:213 – 229.
Driver, H.S., Dijk, D.J., Werth, E., Biedermann, K., Borbe
´ly, A.A. (1996). Sleep and the sleep electro-
encephalogram across the menstrual cycle in young healthy women. J. Clin. Endocrinol. Metab.
81:728– 735.
Ehlers, C.L., Kupfer, D.J. (1997). Slow-wave sleep: do young adult men and women age differently?
J. Sleep Res. 6:211–215.
Elsenbruch, S., Harnish, M.J., Orr, W.C. (1999). Heart rate variability during waking and sleep in
healthy males and females. Sleep 22:1067–1071.
Frankel, B.L., Coursey, R.D., Buchbinder, R., Snyder, F. (1976). Recorded and reported sleep in
chronic primary insomnia. Arch. Gen. Psychiatry 33:615–623.
Fukuda, N., Honma, H., Kohsaka, M., Kobayashi, R., Sakakibara, S., Kohsaka, S., Koyama, T. (1999).
Gender difference of slow wave sleep in middle aged and elderly subjects. Psychiatry Clin. Neurosci.
53:151– 153.
Goel, N., Kim, H., Lao, R.P. (2005). An olfactory stimulus modifies nighttime sleep in young men and
women. Chronobiol. Int. 22(5):889– 904.
Hayter, J. (1983). Sleep behaviors of older persons. Nurs. Res. 32:242 – 246.
Hoch, C.C., Reynolds, C.F., III, Kupfer, D.J., Berman, S.R., Houck, P.R., Stack, J.A. (1987). Empirical
note: self-report versus recorded sleep in healthy seniors. Psychophysiology 24:293–299.
Hoch, C.C., Reynolds, C.F., III, Kupfer, D.J., Berman, S.R. (1988). Stability of EEG sleep and sleep
quality in healthy seniors. Sleep 11:521–527.
Hoddes, E., Zarcone, V., Smythe, H., Phillips, R., Dement, W.C. (1973). Quantification of Sleepiness: a
new approach. Psychophysiology 10:431– 436.
Horne, J.A., O
¨stberg, O. (1976). A self-assessment questionnaire to determine morningness-evening-
ness in human circadian rhythms. Int. J. Chronobiol. 4:97–110.
Hume, K.I., Van, F., Watson, A. (1998). A field study of age and gender differences in habitual adult
sleep. J. Sleep Res. 7:85–94.
Janson, C., Gislason, T., De Backer, W., Plaschke, P., Bjornsson, E., Hetta, J., Kristbjarnason, H.,
Vermeire, P., Boman, G. (1995). Prevalence of sleep disturbances among young adults in three
European countries. Sleep 18:589–597.
Kader, G.A., Griffin, P.T. (1983). Reevaluation of the phenomena of the first night effect. Sleep
6:67– 71.
Kobayashi, R., Kohsaka, M., Fukuda, N., Honma, H., Sakakibara, S., Koyama, T. (1998). Gender
differences in the sleep of middle-aged individuals. Psychiatry Clin. Neurosci. 52:186– 187.
Lee, K.A., Shaver, J.F., Giblin, E.C., Woods, N.F. (1990). Sleep patterns related to menstrual cycle
phase and premenstrual affective symptoms. Sleep 13:403– 409.
Lee, T.M., Hummer, D.L., Jechura, T.J., Mahoney, M.M. (2004). Pubertal development of sex differ-
ences in circadian function: an animal model. Ann. N.Y. Acad. Sci. 1021:262–275.
Li, R.H.Y., Wing, Y.K., Ho, S.C., Fong, S.Y.Y. (2002). Gender differences in insomnia—a study in the
Hong Kong Chinese population. J. Psychosom. Res. 53:601–609.
Lindberg, E., Janson, C., Gislason, T., Bjornsson, E., Hetta, J., Boman, G. (1997). Sleep disturbances in
a young adult population: can gender differences be explained by differences in psychological
status? Sleep 20:381–387.
Lorenzo, J.L., Barbanoj, M.J. (2002). Variability of sleep parameters across multiple laboratory sessions
in healthy young subjects: the “very first night effect.” Psychophysiology 39:409–413.
Manber, R., Armitage, R. (1999). Sex, steroids, and sleep: a review. Sleep 22:540 – 555.
N. Goel, H. Kim, and R. P. Lao914

Mendels, J., Hawkins, D.R. (1967). Sleep laboratory adaptation in normal subjects and depressed
patients (“first night effect”). Electroencephalogr. Clin. Neurophysiol. 22:556– 558.
Middelkoop, H.A., Smilde-van den Doel, D.A., Neven, A.K., Kamphuisen, H.A., Springer, C.P. (1996).
Subjective sleep characteristics of 1,485 males and females aged 50– 93: effects of sex and age, and
factors related to self-evaluated quality of sleep. J. Gerontol. A. Biol. Sci. Med. Sci. 51:M108 – M115.
Mniszek, D.H. (1988). Brighton sleep survey: a study of sleep in 20 – 45-year olds. J. Int. Med. Res.
16:61– 65.
Rechtschaffen, A., Kales, A. (1968). A Manual of Standardized Terminology, Techniques and Scoring System
for Sleep Stages of Human Subjects. Washington, DC: National Institute of Health.
Rediehs, M.H., Reis, J.S., Creason, N.S. (1990). Sleep in old age: focus on gender differences. Sleep
13:410– 424.
Reynolds, C.F., III, Kupfer, D.J., Taska, L.S., Hoch, C.C., Sewitch, D.E., Spiker, D.G. (1985). Sleep of
healthy seniors: a revisit. Sleep 8:20–29.
Schmidt, H.S., Kaelbling, R. (1971). The differential laboratory adaptation of sleep parameters. Biol.
Psychiatry 3:33– 45.
Shaver, J.L. (2002). Women and sleep. Nurs. Clin. North Am. 37:707 – 718.
Shaver, J.L., Giblin, E., Paulsen, V. (1991). Sleep quality subtypes in midlife women. Sleep 14:18 – 23.
Smolensky, M.H., Hermida, R.C., Haus, E., Portaluppi, F., Reinberg, A. (2005). Biological rhythms,
medication safety, and women’s health. J. Women’s Health 14:38–46.
Tamaki, M., Nittono, H., Hayashi, M., Hori, T. (2005). Examination of the first-night effect during the
sleep-onset period. Sleep 28:195– 202.
Tassi, P., Muzet, A. (2000). Sleep inertia. Sleep Med. Rev. 4:341 – 353.
Touitou, Y., Portaluppi, F., Smolensky, M.H., Rensing, L. (2004). Ethical principles and standards for
the conduct of human and animal biological rhythm research. Chronobiol. Int. 21:161 – 170.
Toussaint, M., Luthringer, R., Schaltenbrand, N., Carelli, G., Lainey, E., Jacqmin, A., Muzet, A.,
Macher, J.P. (1995). First-night effect in normal subjects and psychiatric inpatients. Sleep
18:463– 469.
Tsai, L.L., Li, S.P. (2004). Sleep patterns in college students: gender and grade differences.
J. Psychosom. Res. 56:231–237.
Voderholzer, U., Al-Shajlawi, A., Weske, G., Feige, B., Riemann, D. (2003). Are there gender differ-
ences in objective and subjective sleep measures? A study of insomniacs and healthy controls.
Depress. Anxiety 17:162– 172.
Wauquier, A., van Sweden, B., Lagaay, A.M., Kemp, B., Kamphuisen, H.A. (1992). Ambulatory moni-
toring of sleep-wakefulness patterns in healthy elderly males and females (greater than 88 years):
the “Senieur” protocol. J. Am. Geriatr. Soc. 40:109–114.
Webb, W.B. (1982). Sleep in older persons: sleep structures of 50- to 60-year-old men and women.
J. Gerontol. 37:581– 586.
Webb, W.B., Campbell, S.S. (1979). The first night effect revisited with age as a variable. Waking Sleep-
ing 3:319– 324.
Williams, R.L., Karacan, I., Hursch, C.J. (1974). Electroencephalography (EEG) of Human Sleep: Clinical
Implications. New York, NY: John Wiley and Sons Ltd.
Gender Differences in Polysomnographic Sleep 915