as a percentage of change from the baseline condition
as the reference using the absolute value in millimetres
(rated on the visual analogue scale).Nodata were missing
in the analyses.
RESULTS
Sixty five observers rated each of the 46 photographs
for attractiveness, health, and tiredness: 138 ratings by
each observer and 2990 ratings for each of the three
factors rated. When sleep deprived, people were
rated as less healthy (visual analogue scale scores,
mean 63 (SE 2) v 68 (SE 2)), more tired (53 (SE 3) v 44
(SE 3)), and less attractive (38 (SE 2) v 40 (SE 2);
P<0.001 for all) than after a normal night’s sleep
(table 1). Compared with the normal sleep condition,
perceptions of health and attractiveness in the sleep
deprived condition decreased on average by 6% and
4% and tiredness increased by 19%.
A 10 mm increase in tiredness was associated with a
−3.0 mm change in health, a 10 mm increase in health
increased attractiveness by 2.4 mm, and a 10 mm
increase in tiredness reduced attractiveness by
1.2 mm (table 2). These findings were also presented
as correlation, suggesting that faces with perceived
attractiveness are positively associated with perceived
health (r=0.42, fig 1) and negatively with perceived
tiredness (r=−0.28, fig 1). In addition, the average
decrease (for each face) in attractiveness as a result of
deprived sleep was associated with changes in tiredness
(−0.53, n=23, P=0.03) and in health (0.50, n=23,
P=0.01). Moreover, a strong negative association was
found between the respective perceptions of tiredness
and health (r=−0.54, fig 1). Figure 2 shows an example
of observer rated faces.
To evaluate the mediation effects of sleep loss on
attractiveness and health, tiredness was added to the
models presented in table 1 following
recommendations.16 The effect of sleep loss was significantly
mediated by tiredness on both health (P<0.001)
and attractiveness (P<0.001). When tiredness was
added to the model (table 1) with an estimated coefficient
of −2.9 (SE 0.1; P<0.001) the independent effect
of sleep loss on health decreased from −4.2 to −1.8 (SE
0.5; P<0.001). The effect of sleep loss on attractiveness
decreased from −1.6 (table 1) to −0.62 (SE 0.4;
P=0.133), with tiredness estimated at −1.1 (SE 0.1;
P<0.001). The same approach applied to the model
of attractiveness and health (table 2), with a decrease
Table 2 | Associations between health, tiredness, and attractiveness
Dependent variable Predictor
Fixed effects* SD (SE) random effects†
Coefficient‡ z score P value Observer Face Residual
Health Tiredness −3.0 (0.1) −24 0.001 12 (1) 4 (1) 13 (0)
Attractiveness Health 2.4 (0.1) 17 0.001 11 (1) 5 (1) 11 (0)
Attractiveness Tiredness −1.2 (0.1) −11 0.001 11 (1) 5 (1) 11 (0)
Mixed effects regression models used crossed random intercepts for both observers (those rating photographs) and faces (photographed
participants).
*Estimated coefficient of predictor on dependent variable and result from Wald test of statistical significance.
†Likelihood ratio test was used to test significance of random effects. P<0.001 for all random effects.
‡Change (mm) in dependent variable when predictor variable changes 10 mm.
Health
Attractiveness
0 2 4 6 8 10
0
2
4
6
8
-2
10
Tiredness
Attractiveness
0 2 4 6 8 10
0
2
4
6
8
-2
10
Tiredness
Health
0 2 4 6 8 10
0
2
4
6
8
12
10
Fig 1 | Relations between health, tiredness, and attractiveness
of 46 photographs (two each of 23 participants) rated by 65
observers on 100 mm visual analogue scales, with variation
between observers removed using empirical Bayes’ estimates
RESEARCH
BMJ | ONLINE FIRST | bmj.com page 3 of 5
in the association from 2.4 to 2.1 (SE 0.1; P<0.001) with
tiredness estimated at −0.56 (SE 0.1; P<0.001).
DISCUSSION
Sleep deprived people are perceived as less attractive,
less healthy, and more tired compared with when they
are well rested. Apparent tiredness was strongly related
to looking less healthy and less attractive, which was
also supported by the mediating analyses, indicating
that a large part of the found effects and relations on
appearing healthy and attractive were mediated by
looking tired. The fact that untrained observers
detected the effects of sleep loss in others not only provides
evidence for a perceptual ability not previously
subjected to experimental control, but also supports
the notion that sleep history gives rise to socially relevant
signals that provide information about the bearer.
The adaptiveness of an ability to detect sleep related
facial cues resonates well with other research, showing
that small deviations from the average sleep duration
in the long term are associated with an increased risk of
health problems and with a decreased longevity.817
Indeed, even a few hours of sleep deprivation inflict
an array of physiological changes, including neural,
endocrinological, immunological, and cellular functioning,
that if sustained are relevant for long term
health.7 18-20 Here, we show that such physiological
changes are paralleled by detectable facial changes.
These results are related to photographs taken in an artificial
setting and presented to the observers for only six seconds.
It is likely that the effects reported herewould be larger
in real life person to person situations, when overt behaviour
and interactions add further information. Blink interval and
blink duration areknownto be indicators of sleepiness,21 and
trained observers are able to evaluate reliably the drowsiness
of drivers bywatching their videotaped faces.22 In addition, a
few of the people were perceived as healthier, less tired, and
more attractive during the sleep deprived condition. It
remains to be evaluated in follow-up research whether this
is due to randomerror noise in judgments, or associatedwith
specific characteristicsofobservers or the sleep deprived people
they judge.Nevertheless,webelieve that thepresent findings
can be generalised to a wide variety of settings, but
further studies will have to investigate the impact on clinical
studies and other social situations.
Importantly, our findings suggest a prominent role
of sleep history in several domains of interpersonal
perception and judgment, in which sleep history has
previously not been considered of importance, such
as in clinical judgment. In addition, because attractiveness
motivates sexual behaviour, collaboration, and
superior treatment,13 sleep loss may have consequences
in other social contexts. For example, it has
been proposed that facial cues perceived as attractive
are signals of good health and that this recognition has
been selected evolutionarily to guide choice of mate
and successful transmission of genes.13 The fact that
good sleep supports a healthy look and poor sleep the
reverse may be of particular relevance in the medical
setting, where health estimates are an essential part. It
is possible that people with sleep disturbances, clinical
or otherwise, would be judged as more unhealthy,
whereas those who have had an unusually good night’s
sleep may be perceived as rather healthy. Compared
with the sleep deprivation used in the present investigation,
further studies are needed to investigate the
effects of less drastic acute reductions of sleep as well
as long term clinical effects.
Conclusions
People are capable of detecting sleep loss related facial
cues, and these cues modify judgments of another’s
health and attractiveness. These conclusions agree
well with existing models describing a link between
sleep and good health,18 23 as well as a link between
attractiveness and health.13 Future studies should
focus on the relevance of these facial cues in clinical
settings. These could investigate whether clinicians
are better than the average population at detecting
sleep or health related facial cues, and whether patients
Fig 2 | Participant after a normal night’s sleep (left) and after sleep deprivation (right). Faces were presented in a
counterbalanced order
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page 4 of 5 BMJ | ONLINE FIRST | bmj.com
with a clinical diagnosis exhibit more tiredness and are
less healthy looking than healthy people. Perhaps the
more successful doctors are those who pick up on these
details and act accordingly.
Taken together, our results provide important
insights into judgments about health and attractiveness
that are reminiscent of the anecdotal wisdom harboured
in Bell’s words, and in the colloquial notion
of “beauty sleep.”
We thank B Karshikoff for support with data acquisition and M Ingvar for
comments on an earlier draft of the manuscript, both without
compensation and working at the Department for Clinical Neuroscience,
Karolinska Institutet, Sweden.
Contributors: JA designed the data collection, supervised and monitored
data collection, wrote the statistical analysis plan, carried out the
statistical analyses, obtained funding, drafted and revised the
manuscript, and is guarantor. TS designed and carried out the data
collection, cleaned the data, drafted, revised the manuscript, and had final
approval of the manuscript. JA and TS contributed equally to the work. MI
wrote the statistical analysis plan, carried out the statistical analyses,
drafted the manuscript, and critically revised the manuscript. EJWVS
provided statistical advice, advised on data handling, and critically
revised the manuscript. AO provided advice on the methods and critically
revised the manuscript. ML provided administrative support, drafted the
manuscript, and critically revised the manuscript. All authors approved
the final version of the manuscript.
Funding: This study was funded by the Swedish Society for Medical
Research, Rut and Arvid Wolff’s Memory Fund, and the Osher Center for
Integrative Medicine.
Competing interests: All authors have completed the Unified Competing
Int
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