SLEEP 2011 Abstract Supplement

B. Clinical Sleep Science XIII. Sleep and Gender
0897
SEX DIFFERENCE IN INTRINSIC CIRCADIAN PERIOD IN
HUMANS
Duffy JF 1,2 , Cain SW 1,2 , Chang A 1,2 , Phillips AJ 1,2 , Munch MY 1,2,3 ,
Gronfier C 1,2,4,5 , Wyatt JK 1,2,6 , Dijk D 1,2,7 , Wright KP 1,2,8 , Czeisler CA 1,2
1
Division of Sleep Medicine, Department of Medicine, Brigham &
Women’s Hospital, Boston, MA, USA, 2 Division of Sleep Medicine,
Harvard Medical School, Boston, MA, USA, 3 Solar Energy and
Building Physics Laboratory, École Polytechnique Fédérale de
Lausanne, Lausanne, Switzerland, 4 Department of Chronobiology,
INSERM, Bron, France, 5 University of Lyon, Lyon, France, 6 Sleep
Disorders Service and Research Center, Rush University Medical
Center, Chicago, IL, USA, 7 Surrey Sleep Research Centre, University
of Surrey, Guildford, United Kingdom, 8 Sleep and Chronobiology
Laboratory, University of Colorado, Boulder, CO, USA
Introduction: Circadian period is shorter in female rodents than in
males, and exposure to exogenous estrogen shortens period. In humans,
there are sex differences in SCN structure, but conflicting reports of
whether there are sex differences in period. We recently reported that
women have an earlier entrained circadian phase than men, consistent
with either a shorter period or altered light sensitivity in women.
Methods: We conducted a series of forced desynchrony (FD) studies
on 157 healthy participants (52 women, 105 men; mean ± SD age 33.13
± 17.37 years), studied for a total of >4,000 days. In FD, the light-dark/
activity-rest cycle (“T cycle”) is scheduled to be shorter or longer than
24 hours, with low light levels during scheduled wakefulness, resulting
in photic and non-photic influences being distributed across all circadian
phases. Under such conditions, it is possible to estimate the intrinsic period
of the circadian pacemaker with precision. The FD segments lasted
at least two weeks (range 14-43 days), and T-cycles were 11 (n=1), 20
(n=26), 28 (n=114), or 42.85 (n=16) hours. Core body temperature and
blood samples assayed for melatonin were analyzed for determination of
circadian period using non-orthogonal spectral analysis, a method that
accounts for the imposed activity-rest cycle and searches for unknown
periodicity in the circadian range. Sex differences were analyzed with
mixed model ANOVA and Student’s t-tests.
Results: A significant influence of sex on circadian period was observed
for temperature [F(1,155)=8.54, p