Objective
- To systematically
review published population-based studies,
- To carry out a
meta-analysis to assess whether the epidemiology evidence from longitudinal
studies supports the presence of a relationship between short sleep duration
and obesity in children and adolescents.
Method
- Database: Medline,
Cochrane Library, EMBASE and Science Citation Index
- Date: From Jan 1980
through Jan 2015
- No language restrictions
- Included studies: cohort studies, with a measure of
OR/RR/HR, reported on overweight/obesity, exposure of interest was sleep
duration, f/up for at least 1 year, children or adolescent
- Quality Assessment: Newcastle-OttawaScale (NOS), a 9-point
scale that cohorts (0-4 points), the comparability of cohorts (0-2 points), and
the identification of the exposure and the outcomes of study participants (0-3
points). Scores: 0-3, 4-6, and 7-9 for low, moderate, and high quality studies,
respectively
Definition:
i) Obesity/Overweight was defined either as BMI ≥95th percentile
or BMI ≥85th
percentile or BMI ≥25
kg/m2 or BMI ≥ 30
kg/m2 or the International Obesity Task Force (IOTF) BMI cut-offs
ii) Short sleep duration (depend on study): <12h or 11.5h
or <10.5h or <10h or <8h or <7.5h, or <6h per night; or <50th
or <25th percentile; or unclear
The authors categorized short sleep duration and reference
sleep duration using the recommendations of Sleep Health Foundation (SHF)
Results
Characteristics of Included Studies
- 13 studies (50 cohorts; n=35,540), published between
2005-2013
- Study locations: 6 in US, 2 in Europe, 2 in Australia and
3 in Canada
- All studies assessed sleep duration by questionnaire and obesity
outcome by BMI
- Median quality scores: 5.5 (range 4-7)
- Major confounding factors adjusted were: age, gender, BMI,
physical activity and parental income
Main analysis
- Short sleep duration was significantly associated with the
risk of future obesity (OR, 1.71; CI, 1.36-2.14; I2= 91.3%)
- The association (OR, 1.72; CI, 1.35-2.18; I2=
91.8%) did not change materially after excluding a large sample size study
- All studies didn’t report separate results for male and
female. Thus, pooled measures were not calculated separately by gender for
these studies
Subgroup analysis
i) Follow-up years: OR 1.88 (95% CI, 1.57-2.24) for < 5
years and 1.43 (95% CI, 1.09-1.88) for ≥
5 years)
ii) Study location: Significant association was found among
children in USA, Canada, Europe and Australia
iii) SHF recommendations: The effect appeared similar between
short sleep groups of ≥SHF recommendation (OR, 1.50; 95%CI, 1.21-1.85) and
other category (OR, 1.81; 95% CI, 1.35-2.42) was significantly associated with
obesity. The significant association was also found in the reference sleep
duration ≥SHF recommendation
reported the strongest association (OR, 1.89; 95%CI, 1.59-2.23), but not in
other category (OR, 1.28; 95%CI, 0.95-1.72).
-The heterogeneity of effect may due to differences in
geographical location, cut-off for short sleep duration and definition of
obesity/overweight
Sensitivity analysis
- Excluded each single study in turn and pooled the results
of the remaining included studies, the summary OR of obesity ranged from 1.63
(1.32-2.01) to 1.78(1.52-2.08) for short sleep duration
- No individual study had excessive influence on the pooled
effect between risk of obesity and sleep duration
Publication bias
- No significant publication bias for the analysis between
obesity risk and sleep duration (Egger test intercept = 1.76; P = 0.07;
Duvall and Tweedie adjusted OR, 1.53; 95% CI, 1.25-2.00; number of imputed studies
= 0)
Discussion
- Children and adolescents who sleep fora shorter duration
have approximately twice the odds of overweight/obesity compared with those who
sleep for longer duration.
-Several potential causal pathways linking short sleep
duration with obesity have been suggested based on experimental studies of
sleep deprivation:
i) Sleep deprivation might predispose to weight gain is by increasing
caloric intake- Animal studies found that sleep deprivation produces
hyperplasia;
ii) Associations between inadequate sleep and alterations in
leptin and ghrelin, which lead to increased appetite and subsequently increased
food intake;
iii) Short sleep duration could lead to obesity by
increasing the time available to eat, and
iv) Decrease energy expenditure by increasing fatigue as
well as changes in thermoregulation
Limitation
- High level of heterogeneity
- None of the studies included patients from Africa, Latin
America or China, which may limit
the generalisability of our results to African or other populations.
- Information on sleep duration and obesity/overweight was
self-reported by questionnaires in all selected studies
Conclusion
- Short sleep duration was significantly associated with
future obesity among children/adolescents.
- Weight gain appears to be a late consequence of short sleep
duration.
- Sleep duration has been recognised as an easily amendable
risk factor for obesity, which increasing sleep among children may play an
important role in prevention and treatment of obesity
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