Daytime napping, sleep duration and serum C reactive protein: a population-based cohort study.
OBJECTIVE
To explore whether daytime napping and sleep duration are linked to serum C reactive protein (CRP), a pro-inflammatory marker, in an older aged British population.


METHODS
Cross-sectional study.


METHODS
European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk study.


METHODS
A total of 5018 men and women aged 48-92 years reported their sleep habits and had serum CRP levels measured.


METHODS
CRP was measured (mg/L) during 2006-2011 in fresh blood samples using high-sensitivity methods. Participants reported napping habits during 2002-2004, and reported sleep quantity during 2006-2007. Multivariable linear regression models were used to examine the association between napping and log-transformed CRP, and geometric mean CRP levels were calculated.


RESULTS
After adjustment for age and sex, those who reported napping had 10% higher CRP levels compared with those not napping. The association was attenuated but remained borderline significant (β=0.05 (95% CI 0.00 to 0.10)) after further adjustment for social class, education, marital status, body mass index, physical activity, smoking, alcohol intake, self-reported health, pre-existing diseases, systolic blood pressure, hypnotic drug use, depression and in women-only hormone replacement therapy use. The geometric means (95% CI) of CRP levels were 2.38 (2.29 to 2.47) mg/L and 2.26 (2.21 to 2.32) mg/L for those who reported napping and no napping, respectively. A U-shaped association was observed between time spent in bed at night and CRP levels, and nighttime sleep duration was not associated with serum CRP levels. The association between napping and CRP was stronger for older participants, and among extremes of time spent in bed at night.


CONCLUSIONS
Daytime napping was associated with increased CRP levels in an older aged British population. Further studies are needed to determine whether daytime napping is a cause for systemic inflammation, or if it is a symptom or consequence of underlying health problems.
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Yue
Y
Leng
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Sara
S
Ahmadi-Abhari
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Nick W J
NW
Wainwright
Division of Mental Health & Wellbeing, Warwick Medical School, University of Warwick, Coventry, UK.
Francesco P
FP
Cappuccio
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Paul G
PG
Surtees
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Robert
R
Luben
Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge, Cambridge, UK.
Carol
C
Brayne
Department of Public Health and Primary Care, Strangeways Research Laboratory, University of Cambridge, Cambridge, UK.
Kay-Tee
KT
Khaw
D000368:Aged; D000369:Aged, 80 and over; D002097:C-Reactive Protein / Q000032:analysis*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006184:Habits; D006801:Humans; D008297:Male; D008875:Middle Aged; D012890:Sleep; D011795:Surveys and Questionnaires; D013997:Time Factors
D002097:C-Reactive Protein
C-reactive protein; Inflammation; Napping; Population; Sleep