Diurnal and circadian variation of sleep and alertness in men vs. naturally cycling women.
This study quantifies sex differences in the diurnal and circadian variation of sleep and waking while controlling for menstrual cycle phase and hormonal contraceptive use. We compared the diurnal and circadian variation of sleep and alertness of 8 women studied during two phases of the menstrual cycle and 3 women studied during their midfollicular phase with that of 15 men. Participants underwent an ultradian sleep-wake cycle (USW) procedure consisting of 36 cycles of 60-min wake episodes alternating with 60-min nap opportunities. Core body temperature (CBT), salivary melatonin, subjective alertness, and polysomnographically recorded sleep were measured throughout this procedure. All analyzed measures showed a significant diurnal and circadian variation throughout the USW procedure. Compared with men, women demonstrated a significant phase advance of the CBT but not melatonin rhythms, as well as an advance in the diurnal and circadian variation of sleep measures and subjective alertness. Furthermore, women experienced an increased amplitude of the diurnal and circadian variation of alertness, mainly due to a larger decline in the nocturnal nadir. Our results indicate that women are likely initiating sleep at a later circadian phase than men, which may be one factor contributing to the increased susceptibility to sleep disturbances reported in women. Lower nighttime alertness is also observed, suggesting a physiological basis for a greater susceptibility to maladaptation to night shift work in women.
Centre for Study and Treatment of Circadian Rhythms, Douglas Mental Health University Institute, Department of Psychiatry, McGill University, Montreal, QC, Canada H4H 1R3; diane.boivin@douglas.mcgill.ca.
Diane B
DB
Boivin
Department of Medicine, Columbia University, New York, NY 10032;
Ari
A
Shechter
Centre for Study and Treatment of Circadian Rhythms, Douglas Mental Health University Institute, Department of Psychiatry, McGill University, Montreal, QC, Canada H4H 1R3;
Philippe
P
Boudreau
Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada B3H 4R2;
Esmot Ara
EA
Begum
Clinical Research Division, Douglas Mental Health University Institute, Department of Psychiatry, McGill University, Montreal, QC, Canada H4H 1R3.
Ng Mien Kwong
NM
Ng Ying-Kin
D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D001831:Body Temperature / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000378:metabolism; D008597:Menstrual Cycle / Q000502:physiology*; D012463:Saliva / Q000378:metabolism; D012727:Sex Characteristics; D012890:Sleep / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology*; D055815:Young Adult
D015415:Biomarkers; D008550:Melatonin
circadian variation of alertness; circadian variation of sleep; core body temperature; melatonin; sex difference