Adverse metabolic and cardiovascular consequences
of circadian misalignment
Frank A. J. L. Scheera,b,1, Michael F. Hiltona,2, Christos S. Mantzorosb,c, and Steven A. Sheaa,b
aDivision of Sleep Medicine, Brigham and Women’s Hospital, Boston, MA 02115;bHarvard Medical School, Harvard University, Boston, MA 02115;
andcDivision of Endocrinology, Diabetes, and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA 02215
Edited by Joseph S. Takahashi, Northwestern University, Evanston, IL, and approved January 16, 2009 (received for review August 19, 2008)
There is considerable epidemiological evidence that shift work is
associated with increased risk for obesity, diabetes, and cardio-
vascular disease, perhaps the result of physiologic maladaptation
to chronically sleeping and eating at abnormal circadian times. To
begin to understand underlying mechanisms, we determined the
effects of such misalignment between behavioral cycles (fasting/
feeding and sleep/wake cycles) and endogenous circadian cycles
on metabolic, autonomic, and endocrine predictors of obesity,
diabetes, and cardiovascular risk. Ten adults (5 female) underwent
a 10-day laboratory protocol, wherein subjects ate and slept at all
phases of the circadian cycle—achieved by scheduling a recurring
28-h ‘‘day.’’ Subjects ate 4 isocaloric meals each 28-h ‘‘day.’’ For 8
days, plasma leptin, insulin, glucose, and cortisol were measured
hourly, urinary catecholamines 2 hourly (totaling ?1,000 assays/
subject), and blood pressure, heart rate, cardiac vagal modulation,
oxygen consumption, respiratory exchange ratio, and polysomno-
graphic sleep daily. Core body temperature was recorded contin-
uously for 10 days to assess circadian phase. Circadian misalign-
ment, when subjects ate and slept ?12 h out of phase from their
habitual times, systematically decreased leptin (?17%, P < 0.001),
increased glucose (?6%, P < 0.001) despite increased insulin
(?22%, P ? 0.006), completely reversed the daily cortisol rhythm
(P < 0.001), increased mean arterial pressure (?3%, P ? 0.001), and
reduced sleep efficiency (?20%, P < 0.002). Notably, circadian
misalignment caused 3 of 8 subjects (with sufficient available data)
to exhibit postprandial glucose responses in the range typical of a
prediabetic state. These findings demonstrate the adverse cardio-
metabolic implications of circadian misalignment, as occurs acutely
with jet lag and chronically with shift work.
autonomic nervous system ? diabetes ? glucose metabolism ? leptin ?
and cardiovascular disease (2–6). The endogenous circadian
timing system, including the suprachiasmatic nucleus (SCN) in
the hypothalamus and peripheral oscillators in vital organs,
optimally regulates much of our physiology and behavior across
the 24-h day when it is properly aligned with the sleep/wake
cycle. However, shift work is generally associated with chronic
misalignment between the endogenous circadian timing system
and the behavioral cycles, including sleep/wake and fasting/
feeding cycles (7, 8). Shift workers often experience symptoms
akin to jet lag, with gastrointestinal complaints, fatigue, and
sleepiness during the scheduled wake periods, and poor sleep
during the daytime sleep attempts (9). Moreover, chronic cir-
cadian misalignment has been proposed to be the underlying
of shift work (10, 11). The SCN regulates circadian rhythms in
leptin, plasma glucose, glucose tolerance, corticosteroids, and
cardiovascular function via neural and/or humoral signals to the
white adipose tissue, liver, pancreas, adrenal cortex, and heart
(10). Thus, we assessed in humans the independent effects of the
circadian system and the behavioral cycle (including fasting/
feeding and sleep/wake cycles) on metabolic, autonomic, and
pproximately 8.6 million Americans perform shift work (1),
which is associated with increased risk of obesity, diabetes,
endocrine function. We also tested how these effects on cardio-
metabolic function interact when circadian and behavioral cycles
are misaligned (i.e., when waking and eating during the ‘‘bio-
logical night’’), as typically occurs with shift work.
of the circadian cycle was achieved in a laboratory study by
uniformly distributing the behavioral cycle across all phases of
the circadian cycle (Fig. 1).
Effects of Behavioral Cycle. The effects of the behavioral cycle,
independent of the circadian cycle, on leptin, glucose, insulin,
epinephrine, norepinephrine, and cortisol are shown in Fig. 2,
Left panels. Leptin varied significantly across the behavioral
cycle, with a trough around breakfast and a peak after the last
meal, coinciding with the onset of the scheduled sleep episode
(P ? 0.001, peak-to-trough 44%). Also, both glucose and insulin
varied significantly across the behavioral cycle (glucose: P ?
0.001, peak-to-trough 26%; insulin: P ? 0.001, peak-to-trough
158%), presumably the result of the timing of meals. Both
epinephrine and norepinephrine varied significantly across the
behavioral cycle with peaks during the wake episode and troughs
during the sleep episode (epinephrine: P ? 0.001, peak-to-
trough 83%; norepinephrine: P ? 0.001, peak-to-trough 72%).
Cortisol varied significantly across the behavioral cycle, peaking
after awakening and with a trough at the onset of the scheduled
sleep episode (P ? 0.001, peak-to-trough 38%).
Effect of Circadian Cycle. The effects of the circadian cycle,
independent of the behavioral cycle, on leptin, glucose, insulin,
epinephrine, norepinephrine, and cortisol, are shown in Fig. 2,
Right panels. Glucose had a significant endogenous circadian
rhythm (P ? 0.018, peak-to-trough 4%), with a peak during the
06:30 in these subjects). Epinephrine exhibited a significant
endogenous circadian rhythm (P ? 0.001, peak-to-trough 53%),
with a peak during the biological day (circadian bin 180°;
equivalent to ?14:30–18:30). Cortisol had a significant endog-
enous circadian rhythm (P ? 0.001, peak-to-trough 113%), with
a peak at the end of the biological night (60°; close to habitual
wake time). There were no significant circadian rhythms in
leptin, insulin, or norepinephrine.
Author contributions: M.F.H. and S.A.S. designed research; F.A.J.L.S., M.F.H., C.S.M., and
C.S.M., and S.A.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
1To whom correspondence should be addressed. E-mail: email@example.com.
2Present address: Queensland Centre for Mental Health Research, Sumner Park, BC, QLD
This article contains supporting information online at www.pnas.org/cgi/content/full/
www.pnas.org?cgi?doi?10.1073?pnas.0808180106 PNAS Early Edition ?
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Interaction Between Behavioral and Circadian Cycles. Although the
behavioral and circadian influences are presented independently
above and in Fig. 2, changes across the behavioral and circadian
cycles happen concurrently across the day. Thus, it is necessary
to consider the interaction of these factors to understand what
happens across a normal or across a misaligned day. There was
a clear interaction between the effects of the behavioral cycle
and the circadian cycle upon leptin (P ? 0.001). Leptin was
systematically lower when the behavioral cycle was misaligned
with the circadian cycle. This leptin suppression was maximal
when the behavioral cycle was ?12 h misaligned with the
circadian cycle, as seen on the fourth 28-h cycle in Fig. 3 (red
rectangle) and exemplified by the highlighted trajectory in Fig. S1.
Effects of Circadian Misalignment on Metabolic, Autonomic, and
Endocrine Function. The two 28-h trajectories (aligned normally
vs. misaligned) as depicted for leptin in Fig. S1 are shown vs.
scheduled time of awakening for leptin and other variables in
Fig. 4. Leptin was 17% lower (P ? 0.001) across the entire
behavioral cycle when misaligned compared to when aligned
normally. Glucose was 6% higher (P ? 0.001) and insulin was
22% higher (P ? 0.006) across the entire behavioral cycle when
misaligned. The increase in glucose seemed to be the result of an
exaggerated postprandial glucose response (average 3-h post-
prandial glucose comparing misaligned to aligned: breakfast
?21%, lunch ?12%, and dinner ?11%) and not the result of
elevated fasting levels (Fig. 4). Moreover, during normal circa-
dian alignment (wake time ?08:00), none of the 10 subjects had
signs of impaired glucose tolerance, but during maximal mis-
alignment (wake time ?20:00), 3 of 8 subjects in whom glucose
metabolism could be assessed had meal responses consistent
with a prediabetic state (?140 mg/dL, 2-h postprandial glucose
values) or diabetic state (?199 mg/dL) (Fig. 5, Top panel).
Average 2-h postprandial breakfast plasma glucose in these 8
subjects increased from 99.9 ? 4.5 mg/dL when aligned to 132 ?
13 mg/dL when misaligned (P ? 0.025; Wilcoxon matched pairs
test). The increased glucose levels occurred despite a concom-
itant increase in insulin values (from 23.3 ? 5.6 to 49.9 ? 14.0
?IU/mL; P ? 0.036; Fig. 5, Bottom panel), which implies a
decrease in insulin sensitivity and insufficient ?-cell compensa-
tion during misalignment. In contrast, cortisol, epinephrine, and
norepinephrine were not different across the behavioral cycle
when subjects were misaligned. For cortisol, the most dramatic
change induced by misalignment was a complete inverse pattern
across the sleep/wake cycle, resulting in lower levels at the
beginning and higher levels at the end of the wake episode (P ?
0.001, interaction effects between alignment and behavioral
cycle). This is consistent with the dominant role of the circadian
system on cortisol regulation relative to the effect of the
behavioral cycle. Epinephrine was lower during wakefulness
when misaligned (P ? 0.002, interaction effect), likely the result
of the circadian system inhibiting epinephrine during the bio-
logical night even when subjects remained awake. From mea-
surements during wakefulness only, mean arterial blood pressure
was 3% higher (3 mm Hg; P ? 0.001) when misaligned, while
there was no measurable effect of misalignment on oxygen
consumption, respiratory exchange ratio, heart rate, or cardiac
vagal control [as estimated by logHF (12)]. Similar to leptin,
sleep efficiency was significantly lower when misaligned (67% vs.
84%; P ? 0.002 Student’s t test; n ? 9 with complete sleep
leptin, we attempted to determine whether circadian misalign-
ment itself influences leptin beyond any effect of sleep. From
correlation analyses, it appeared that circadian misalignment
nights, followed by the FD portion of the study consisting of 7 recurring 28-h
‘‘days’’ in dim light (example subject had habitual bedtime of 24:00). Thick
pulmonary function measurements); gray bars, meal times; B, breakfast; L,
lunch; D, dinner; S, snack; thin open horizontal bars, waking episodes of days
1 and 2 at room light intensity (?90 lux); thin black horizontal bars, waking
episodes on days 3–11 in dim light (?1.8 lux).
metabolic, autonomic, and endocrine function. Left panels: influence of
behavioral cycle, independent from circadian cycle. Right panels: influence of
endogenous circadian cycle, independent from behavioral cycle. Error bars,
as in Fig. 1; vertical dotted line, fitted core body temperature minimum;
circadian cycles (Right panels). Glucose and epinephrine scales are on the left
Independent influence of circadian cycle and behavioral cycle on
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had a stronger effect on leptin (Spearman’s rho ? ?0.69; P ?
0.001) than did sleep efficiency (Spearman’s rho ? 0.34; P ?
0.006). In a complementary analysis when including sleep effi-
ciency as a covariate, circadian misalignment still significantly
affected leptin (P ? 0.001) without a significant effect of sleep
efficiency (P ? 0.34). These results suggest that circadian
misalignment itself impacts leptin beyond any effect induced by
changes in sleep.
Potential Health Consequences of Shift Work and Jet Lag. We found
that short-term circadian misalignment, similar to that which
occurs acutely with jet lag and chronically with shift work, results
arterial pressure, systematic decreases in leptin and sleep effi-
ciency, and the complete inversion of the cortisol profile across
the behavioral cycle. The abnormally high cortisol at the end of
the wake episode and beginning of the sleep episode when
misaligned (Fig. 4 Lower Right panel) could contribute to insulin
resistance and hyperglycemia (13, 14). Also, decreased leptin
stimulates appetite and decreases energy expenditure, which—if
obesity. Decreased sleep is associated with increased risk for
obesity, diabetes, and hypertension (15–17). These combined
effects during circadian misalignment may provide a mechanism
underlying the increased risk for obesity, hypertension, and
diabetes in shift workers (3, 5, 6).
Others have examined the effect of simulated night shift work
on postprandial glucose and insulin with varied results (18, 19).
Interpretation of these studies is complicated due to differences
in premeal conditions between the night and day shifts (e.g.,
duration of wakefulness before test meals), such that the effects
‘‘day,’’ indicated in red rectangle) as compared to circadian alignment (indi-
cated in green rectangle). Circles, mean; error bars, SEM; gray area, mean ?
SEM on first 28-h day replotted for comparison (circadian alignment); hori-
zontal black bars, scheduled sleep episodes; vertical lines, scheduled awaken-
of the scheduled wake time on each 28-h day.
Circadian misalignment suppressed leptin levels proportionally, with
(cortisol) and 28-h cycle for variables mainly driven by behavioral cycle (others)]; gray area, scheduled sleep episode; short vertical gray bars, meal times as in Fig. 1.
Consequences of circadian misalignment on metabolic, autonomic, and endocrine function. Data are plotted according to time-since-wake, during normal
Scheer et al.PNAS Early Edition ?
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of circadian misalignment alone could not be assessed. Our study
design addressed this limitation by scheduling meals at the same
time since awakening and we found systematically increased
postprandial glucose and insulin and thereby decreased insulin
sensitivity, as previously suggested by the results of a real-life
shift work protocol (20).
Recently, the same molecular and genetic factors, including
transcription-translation feedback loops that control the SCN
outputs have been found in various peripheral organs, which,
together with humoral and neural signals, seem to drive organ
functions (21). In rodents, such peripheral or extra-SCN circa-
dian oscillators in the liver and brain can be dissociated from the
central circadian pacemaker by restricted food access at abnor-
mal times (22, 23). A functional molecular circadian clock
selectively in the SCN is sufficient to drive light-entrainment of
various circadian rhythms, while a functional clock in the dor-
somedial hypothalamus may be sufficient to drive food entrain-
ment [(24) although this is still debated, e.g., (25)]. Whether
meals scheduled at abnormal circadian times, as occurs during
shift work, also leads to such ‘‘internal desynchronization’’ in
humans has yet to be determined. In some animal models,
repeated shifts in the light/dark cycle—typical of shift work—
leads to premature death, while mutations of circadian clock
genes can lead to signs of metabolic syndrome (11, 26, 27),
supporting the potential negative health consequences of circa-
The 3-mm Hg increase in mean arterial pressure during
short-term circadian misalignment is similar in magnitude to the
effect of the 3-week Dietary Approaches to Stop Hypertension
important (29). Because blood pressure changes are typically
hemodynamic effect of chronic misalignment such as occurs with
shift work may have greater clinical implications in vulnerable
populations (2, 4).
Potential Mechanisms Involved in Effects of Circadian Misalignment.
We measured numerous interacting variables to help determine
causal links underlying changes induced by circadian misalign-
ment. The decrease in leptin during circadian misalignment
could not be explained by a simultaneous decrease in the
measured variables that have been shown to stimulate leptin
secretion, namely glucose, insulin, cortisol, vagal tone, or food
intake; or by an increase in those measured variables that can
inhibit leptin: epinephrine, norepinephrine, or metabolic rate; or
by a change in metabolic substrate (as suggested by respiratory
exchange ratio) (30–32). Both short-term experimental sleep
restriction (33) and chronic self-reported short sleep duration
during circadian misalignment in the current study may contrib-
ute to the decrease in leptin. However, the analyses of the effect
of sleep efficiency and circadian misalignment on leptin, sepa-
rately and combined, suggest that circadian misalignment itself
mainly impacts leptin independently of its effects on sleep. It will
be useful in future studies to determine the effect of circadian
misalignment on other potential effector mechanisms of leptin
regulation, such as digestive effectiveness (35), cytokines, free
fatty acids, growth hormone and other growth factors (31). For
instance, misalignment between meal times and central and/or
peripheral (e.g., gastrointestinal) circadian rhythms (35) might
result in decreased digestion and energy uptake from meals,
leading to a negative energy balance and suppressed leptin. The
observations of a decrease in leptin within a few days contrast
with the model of leptin as a long-term mediator of energy
balance and instead support a model involving a role for leptin
as a short-term mediator of energy balance in response to an
altered behavioral state.
The increased postprandial glucose in the face of increased
insulin implies a decrease in insulin sensitivity and insufficient
?-cell compensation during misalignment, which could have
directly been caused by the decreased leptin during circadian
misalignment or changes in other factors, including other adi-
pokines (31, 36, 37). Notably, the increase in glucose seemed to
be due to an exaggerated postprandial glucose response rather
than elevated fasting glucose (Fig. 4 Left Middle panel), suggest-
ing that misalignment may impact fat/muscle metabolism or
?-cell function more than hepatic gluconeogenesis. Recent
evidence in humans of increased risk for type 2 diabetes in a
genetic variant of melatonin 1B receptor (Mel1B), expression of
Mel1B in pancreatic ?-cells, and inhibition of glucose-induced
insulin release by melatonin (38, 39), raises the possibility that
the reversal of the melatonin profile relative to the feeding/
fasting cycle contributed to insufficient ?-cell compensation
when misaligned (for plasma melatonin data, see Fig. S2).
Future mechanistic studies will be needed to fully clarify under-
The observed increase in blood pressure while awake during
circadian misalignment was not associated with increased heart
rate and could not be explained by an increase in the measured
variables that can increase blood pressure: epinephrine, norepi-
nephrine, cortisol, or by a decrease in vagal tone, or by an
underlying circadian rhythm in blood pressure (40). Future
studies are required to investigate whether circadian misalign-
ment leads to increased total peripheral resistance, stroke vol-
ume, or blood volume.
The observed decrease in sleep efficiency during circadian
misalignment has previously been noted and is explained by a
circadian rhythm in sleep propensity, with a minimum during the
biological day (41).
The forced desynchrony (FD) protocol permits analysis of the
separate circadian and behavioral effects, and their interaction.
The FD uncovered a large effect of the behavioral cycle inde-
pendent of the circadian cycle, not only on plasma glucose,
insulin, and leptin, but also on epinephrine and norepinephrine,
tivity. During circadian misalignment, 2-h postprandial glucose (Top panel)
and insulin (Bottom panel) levels were significantly increased as compared to
normal alignment. Dotted lines, 140 mg/dL and 200 mg/dL 2-h postprandial
glucose, above which levels are considered prediabetic and diabetic, respec-
tively; P-values, statistical significance for effect of misalignment.
Circadian misalignment reduces glucose tolerance and insulin sensi-
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both with peak-to-trough variation of ?80% peaking during the
middle of the wake episode, and on cortisol, with a peak-to-
trough variation of ?45% peaking following scheduled awak-
ening (Fig. 2 Left panels). In addition, the FD uncovered
impressive endogenous circadian influences independent of the
behavioral cycle on epinephrine and cortisol, with a peak-to-
trough variation of ?50% and ?110%, respectively (Fig. 2 Right
panels). Remarkably, for cortisol the circadian effect was more
than twice the size of the combined effects of the sleep/wake
cycle, meals, and activity. For epinephrine, the circadian effects
were of similar magnitude as these combined behavioral effects.
with a peak-to-trough variation of 4%, peaking during the
biological night, consistent with previous observations (42).
The absence of a significant circadian variation in leptin and
insulin could have been caused by masking effects of the large
meals in the FD protocol, as opposed to small evenly spaced
isocaloric snacks or continuous enteral nutrition in other studies
with evidence for circadian control of leptin (43, 44). Alterna-
tively, the feeding/fasting cycle may have entrained peripheral
oscillators. In rodents, peripheral oscillators such as in the liver
can be dissociated from the master oscillator in the hypothala-
mus by restricted daytime food access (22). However, it remains
to be determined whether meals are also strong zeitgebers in
humans (who can survive starvation much longer than rodents).
that meals are the most dominant factor controlling the daily
leptin profile in humans, but it will require future studies to
determine whether these effects are caused by meals directly
(masking a circadian cycle) or by entrainment of either central
or peripheral circadian oscillators.
Because of nonadditive interactions, the effects of circadian
misalignment cannot always be predicted by simply summating the
behavioral and circadian cycle effects, as best demonstrated for
leptin (Figs. 2, 3, 4, and S1). Knowledge of the differential effects
of these mechanisms may be important in determining counter-
measures for maladaptation to circadian misalignment, targeting
either the circadian system or specific behaviors, or even specific
behaviors when they occur at specific circadian phases.
Summary. Circadian misalignment, a condition that is highly
prevalent in shift workers, resulted in a decrease in leptin,
increase in glucose and insulin, increase in mean arterial blood
pressure, and reduced sleep efficiency. The strengths of the
current study include the: (i) experimental evidence supporting
epidemiological findings; (ii) within-subject design; (iii) con-
trolled environmental and behavioral conditions; (iv) compre-
hensive assessment of endocrine, metabolic, and autonomic
function and sleep efficiency; and (v) ability to investigate the
separate circadian, separate behavioral, and interaction effects
on these primary outcome variables. The small number of
the inclusion of subjects with mild asthma are limitations. Future
laboratory and field studies are needed to investigate in more
detail the mechanisms and chronic effects of the cardiometa-
bolic changes observed during circadian misalignment.
Materials and Methods
The protocol was approved by the institutional Human Research Committee,
and written informed consent was obtained from participants. Cardiopulmo-
nary and cognitive data from the same study have been published elsewhere
Subjects. We studied 10 adult subjects [5 female; mean age 25.5 years (range
19–41 years); mean body mass index 25.1 kg/m2(20–28 kg/m2)]. Subjects were
by history, physical, 12-lead ECG, chest X-ray, complete blood count, blood and
none of the subjects were on steroid medication and we were unable to detect
any impact of the presence of mild asthma on any of the main effects.
Protocol. To ensure a stable circadian phase angle of entrainment at baseline,
subjects initially maintained a regular sleep–wake schedule for ?2 weeks,
including 8-h sleep opportunity at their average habitual times, and then
(Fig. 1). The laboratory protocol consisted of 2 baseline days and nights, with
8-h sleep opportunities at habitual times, followed by 7 recurring 28-h sleep–
light on the circadian system. This FD protocol desynchronizes, or uncouples,
the behavioral cycles from the circadian cycles by distributing sleep and
independent and interacting effects of the circadian system and behavioral
cycles of sleep/fasting and wake/eating (50). During each 28-h ‘‘day,’’ subjects
had standardized breakfast, lunch, dinner, and a snack at 1 h, 5 h, 11.5 h, and
15.5 h post-awakening, respectively. Meals were composed of 25% fat, 50%
carbohydrate, and 25% protein. The overall calories per unit of time were
fast) following a 13-h fast was used to assess glucose tolerance during normal
?08:00) and during circadian misalignment (fourth 28-h sleep/wake cycle;
average scheduled wake time ?20:00). Exercise was prohibited. The ratio of
the scheduled sleep (9 h 20 min) to wake (18 h 40 min) was maintained at 1:2,
as occurred in the home environment.
Measurements and Analysis. Most of the laboratory procedures were the same
as previously published (44, 50). Blood was sampled hourly during both wake-
fulness and sleep via an indwelling catheter in a forearm vein. Plasma leptin,
assayed using a chemiluminescent assay with a sensitivity of 0.26 ?g/dL. Urinary
epinephrine and norepinephrine were assayed using a radioimmunoassay (RIA)
with a sensitivity of 12 pg/mL and 24 pg/mL, respectively.
On 4 occasions spread evenly throughout each wake episode, subjects lay
semireclined in bed for ?1 h while arterial blood pressure, oxygen consump-
consumption) were measured. An ECG was recorded during volitionally con-
trolled breathing at 10 breaths/min for derivation of heart rate and markers
of cardiac vagal control [high frequency heart rate variability (HF); 0.15–0.40
Hz] from spectral analyses of interbeat intervals (12). Recordings of 2 electro-
encephalograms, 2 electrooculograms, and a submental electromyogram
were made for quantification of sleep. Core body temperature was measured
throughout using a rectal thermistor for assessment of phase and period of
the circadian pacemaker (50). All data were assigned a circadian phase de-
pending upon the time from the fitted core body temperature minimum (0°)
expressed in normalized units (i.e., percentage difference from individual’s
for any individual linear trend across the FD). Individuals’ normalized data
scheduled awakening. The independent effects of the behavioral cycle, the
independent effects of the circadian cycle, and any interaction effects were
using 3-factor mixed model analysis of variance with restricted maximum
likelihood (REML) estimates of the variance components (JMP, SAS Institute).
To specifically test the effects of misalignment between the behavioral cycles
and the circadian cycle, data were grouped into 1-h bins according to time
since scheduled awakening and the 28-h profiles of variables were compared
when aligned normally (i.e., when waking and eating during the biological
day on the first FD cycle, with average scheduled wake time of ?08:00) and
when maximally misaligned as occurs in shift work (i.e., when waking and
eating during the biological night on the fourth FD cycle, with average
scheduled wake time of ?20:00). The independent effects of alignment (FD
cycle 1 vs. 4), the independent effects of the behavioral cycle, and any
analysis of variance using REML. All data are presented as mean ? SEM.
sleep efficiency and circadian misalignment across the whole FD protocol,
Spearman’s rank correlations were performed between the average leptin
levels during each scheduled wake episode and 4 levels of circadian misalign-
to each category) and 4 categories of sleep efficiency in the preceding sleep
opportunity (sleep efficiency: 90–100%, 80–90%, 70–80%, ?70%; at least 7
Scheer et al.PNAS Early Edition ?
5 of 6
misalignment resulted in suppression of leptin per se, thus independent of a Download full-text
decrease in sleep efficiency, we analyzed these same variables using mixed
model analysis of covariance with circadian misalignment as fixed factor and
sleep efficiency as covariate. Conversion factors from conventional and/or
metric units to Syste `me International units are listed in the SI Text.
ers who participated in this study, including Heather Evoniuk and Taneisha
Benjamin for help with data analysis and Diana Barb for performing the
leptin assays. This work was supported by National Heart, Lung and Blood
Institute Grants R01-HL64815, R01-HL076409, and K24-HL76446 (to S.A.S.),
General Clinical Research Center Grant MO1-RR02635 (to Brigham and
Women’s Hospital), National Center for Complementary and Alternative
Medicine Grant R21-AT002713 (to F.A.J.L.S.), and National Institute of
Diabetes and Digestive and Kidney Diseases Grant R01–57875, and a
discretionary grant from Beth Israel Deaconess Medical Center (to C.S.M.).
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