***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: This pilot aims to better underst and the market for childcare in Saudi Arabia – both the supply and dem and sides – and to design a r and omized controlled experiment to test whether access to affordable day care ( in the form of subsidies , for example ) would incentivize Saudi mothers to search actively for employment and to remain employed once they are hired . In addition , the study seeks to underst and the degree to which employment early on in one ’s life impacts employment in later stages . The pilot will provide information on the groups of women the experiment should target , appropriate levels for the childcare subsidy , and the quality and current geographic locations of daycare sites . Expected Impact Determine the effects of facilitating childcare access on Saudi women ’s employment . PRINCIPAL INVESTIGATORS  Boston University Patricia Cortes  Harvard University Claudia Goldin  Swarthmore College Jennifer In 2007 , the International Agency for Research on Cancer declared shift work that involved circadian disruption to be a " probable " carcinogen ( group 2A ) , noting that human evidence was limited . Using data from 2 prospect i ve cohort studies , the Nurses ' Health Study ( 1988 - 2012 ; n = 78,516 ) and Nurses ' Health Study II ( 1989 - 2013 ; n = 114,559 ) , we examined associations between  rotating night-shift work and breast cancer risk  . In the 2 cohorts , there were a total of 9,541 incident invasive breast malignancies and 24 years of follow-up . In the Nurses ' Health Study , women with 30 years or more of shift work did not have a higher risk of breast cancer ( hazard ratio ( HR ) = 0.95 , 95 % confidence interval ( 95 % CI ) : 0.77 , 1.17 ; P for trend = 0.63 ) compared with those who never did shift work , although follow-up occurred primarily after retirement from shift work . Among participants in the Nurses ' Health Study II , who were younger than participants in the other cohort , the risk of breast cancer was significantly higher in women with 20 years or more of shift work at baseline , reflecting young-adult exposure ( HR = 2.15 , 95 % CI : 1.23 , 3.73 ; P for trend = 0.23 ) , and was marginally significantly higher for women with 20 years or more of cumulative shift work when we used up date d exposure information ( HR = 1.40 , 95 % CI : 1.00 , 1.97 ; P for trend = 0.74 ) . In conclusion , long-term rotating night-shift work was associated with a higher risk of breast cancer , particularly among women who performed shift work during young adulthood . Further studies should explore the role of shift work timing on breast cancer risk CONTEXT Neuroendocrine and immune stresses imposed by chronic sleep restriction are known to be involved in the harmful cardiovascular effects associated with poor sleep . OBJECTIVES Despite a well-known beneficial effect of napping on alertness , its effects on neuroendocrine stress and immune responses after sleep restriction are largely unknown . DESIGN This study was a strictly controlled ( sleep-wake status , light environment , caloric intake ) , crossover , r and omized design in continuously polysomnography-monitored subjects . SETTING The study was conducted in a laboratory-based study . PARTICIPANTS The subjects were 11 healthy young men . INTERVENTION We investigated the effects on neuroendocrine and immune biomarkers of a night of sleep restricted to 2 h followed by a day without naps or with 30 minute morning and afternoon naps , both conditions followed by an ad libitum recovery night starting at 20:00 . MAIN OUTCOME MEASURES Salivary interleukin-6 and urinary catecholamines were assessed throughout the daytime study periods . RESULTS The increase in norepinephrine values seen at the end of the afternoon after the sleep-restricted night was not present when the subjects had the opportunity to take naps . Interleukin-6 changes observed after sleep deprivation were also normalized after napping . During the recovery day in the no-nap condition , there were increased levels of afternoon epinephrine and dopamine , which was not the case in the nap condition . A recovery night after napping was associated with a reduced amount of slow-wave sleep compared to after the no-nap condition . CONCLUSIONS Our data suggest that napping has stress-releasing and immune effects . Napping could be easily applied in real setting s as a countermeasure to the detrimental health consequences of sleep debt Flaws in the design , conduct , analysis , and reporting of r and omised trials can cause the effect of an intervention to be underestimated or overestimated . The Cochrane Collaboration ’s tool for assessing risk of bias aims to make the process clearer and more Background Shift work has been hypothesized as a risk factor for obesity . In this study , we investigated the association between current shift work and body mass index ( BMI ) among female nurses in Korea . The relationship between duration of shift work and BMI of the participants was also evaluated . Methods This cross-sectional survey evaluated participants in the Korean Nurses ’ Survey , conducted from October to December 2011 , using web-based self-administered question naires . A total of 9,989 nurses were included among 10,000 who registered on the survey web site ( 5,287 shift workers and 4,702 non-shift workers ) . Current shift workers were divided into tertiles of shift work duration ( 0.08–3.00 years , n = 1,732 ; 3.08–6.75 years , n = 1,731 ; and 6.83–38.00 years , n = 1,686 ) . The BMI thresholds of overweight and obesity were ≥23 kg/m2 and ≥25 kg/m2 , respectively . Data were analyzed using SPSS software . Results Mean participant age was 33.2 ± 8.6 years and the mean BMI was 20.9 ± 2.5 kg/m2 . There were statistically significant differences in current smoking status , regular drinking habit , dietary habits , regular exercise , sleep problems and self-perceived health status according to duration of shift work . The overall prevalence of overweight/obesity ( 18.6 % ) and obesity ( 7.4 % ) increased significantly as shift work duration increased from the lowest to highest tertile ( P for trend < 0.001 ) . Multivariate logistic regression analysis revealed no association between current shift work and BMI . However , after adjusting for potential confounders , the participants with the longest duration of shift work were 1.63 ( 95 % CI , 1.22–2.17 ) times more likely to be overweight or obese than those with the shortest duration . There was a significant positive association between obesity and shift work duration in the unadjusted analysis ; however , it was attenuated and no longer significant in the multivariate model . Conclusions The duration of shift work was positively associated with prevalence of overweight/obesity  in nurses in Korea . Although these findings need to be confirmed in prospect i ve studies , they suggest that special attention should be paid to female nurses with a long duration of shift work STUDY OBJECTIVES To assess sleep inertia following 10-min and 30-min naps during a simulated night shift . METHODS Thirty-one healthy adults ( aged 21 - 35 y ; 18 females ) participated in a 3-day laboratory study that included one baseline ( BL ) sleep ( 22:00 - 07:00 ) and one experimental night involving r and omization to either : total sleep deprivation ( NO-NAP ) , a 10-min nap ( 10-NAP ) or a 30-min nap ( 30-NAP ) . Nap opportunities ended at 04:00 . A 3-min psychomotor vigilance task ( PVT-B ) , digit-symbol substitution task ( DSST ) , fatigue scale , sleepiness scale , and self-rated performance scale were undertaken pre-nap ( 03:00 ) and at 2 , 17 , 32 , and 47 min post-nap . RESULTS The 30-NAP ( 14.7 ± 5.7 min ) had more slow wave sleep than the 10-NAP ( 0.8 ± 1.5 min ; P < 0.001 ) condition . In the NO-NAP condition , PVT-B performance was worse than pre-nap ( 4.6 ± 0.3 1/sec ) at 47 min post-nap ( 4.1 ± 0.4 1/sec ; P < 0.001 ) . There was no change across time in the 10-NAP condition . In the 30-NAP condition , performance immediately deteriorated from pre-nap ( 4.3 ± 0.3 1/sec ) and was still worse at 47 min post-nap ( 4.0 ± 0.5 1/sec ; P < 0.015 ) . DSST performance deteriorated in the NO-NAP ( worse than pre-nap from 17 to 47 min ; P < 0.008 ) , did not change in the 10-NAP , and was impaired 2 min post-nap in the 30-NAP condition ( P = 0.028 ) . All conditions self-rated performance as better than pre-nap for all post-nap test points ( P < 0.001 ) . CONCLUSIONS This study is the first to show that a 10-min ( but not a 30-min ) nighttime nap had minimal sleep inertia and helped to mitigate short-term performance impairment during a simulated night shift . Self-rated performance did not reflect objective performance following a nap OBJECTIVES To evaluate the effectiveness of a broad , literature -based night shiftwork intervention for enhancement of emergency physicians ' ( EPs ' ) adaptation to night rotations . METHODS A prospect i ve , double-blind , active placebo-controlled study was conducted on 6 attending physicians in a university hospital ED . Three data sets were collected under the following conditions : baseline , after active placebo intervention , and after experimental intervention . In each condition , data were collected when the physicians worked both night and day shifts . Measurements included ambulatory polysomnographic recordings of the main sleep periods , objective performance tests administered several times during the subjects ' shifts , and daily subjective ratings of the subjects ' sleep , moods , and intervention use . RESULTS The subjects slept an average of 5 hr 42 min across all conditions . After night shifts , the subjects slept significantly less than they did after day shifts ( 5 hr 13 min vs 6 hr 20 min ; p < 0.05 ) . The physicians ' vigilance reaction times and times for intubation of a mannequin were significantly slower during night shifts than they were during day shifts ( p = 0.007 and p < 0.04 , respectively ) , but performances on ECG analysis did not significantly differ between night and day shifts . Mood ratings were significantly more negative during night shifts than they were during day shifts ( more sluggish p < 0.04 , less motivated p < 0.03 , and less clear thinking p < 0.04 ) . The strategies in the experimental intervention were used 85 % of the time according to logbook entries . The experimental and active placebo interventions did not significantly improve the physician 's performance , or mood on the night shift , although the subjects slept more after both interventions . CONCLUSIONS Although the experimental intervention was successfully implemented , it failed to significantly improve attending physicians '  sleep , performance , or mood on night shifts . A decrease in speed of intubation , vigilance reaction times , and subjective alertness was evident each time the physicians rotated through the night shift . These findings plus the limited sleep across all conditions and shifts suggest that circadian-mediated disruptions of waking neurobehavioral functions and sleep deprivation are problems in EPs IMPORTANCE Prospect i ve studies linking shift work to coronary heart disease ( CHD ) have been inconsistent and limited by short follow-up . OBJECTIVE To determine whether rotating night shift work is associated with CHD risk . DESIGN , SETTING , AND PARTICIPANTS Prospect i ve cohort study of 189,158 initially healthy women followed up over 24 years in the Nurses ' Health Studies ( NHS [ 1988 - 2012 ] : N = 73,623 and NHS2 [ 1989 - 2013 ] : N = 115,535 ) . EXPOSURES Lifetime history of rotating night shift work  ( ≥3 night shifts per month in addition to day and evening shifts ) at baseline ( up date d every 2 to 4 years in the NHS2 ) . MAIN OUTCOMES AND MEASURES Incident CHD ; ie , nonfatal myocardial infa rct ion , CHD death , angiogram-confirmed angina pectoris , coronary artery bypass graft surgery , stents , and angioplasty . RESULTS During follow-up , 7303 incident CHD cases occurred in the NHS ( mean age at baseline , 54.5 years ) and 3519 in the NHS2 ( mean age , 34.8 years ) . In multivariable-adjusted Cox proportional hazards models , increasing years of baseline rotating night shift work was associated with significantly higher CHD risk in both cohorts . In the NHS , the association between duration of shift work and CHD was stronger in the first half of follow-up than in the second half ( P=.02 for interaction ) , suggesting waning risk after cessation of shift work . Longer time since quitting shift work was associated with decreased CHD risk among ever shift workers in the NHS2 ( P<.00 
    Output:
    
Many nurses experienced napping during their night-shift although no clear policy emerged .
Napping is beneficial to the well-being of nurses and could improve their psychomotor vigilance and performance .
The evidence on reducing sleepiness and fatigue was also insufficient and napping in nursing still faces challenges .
Although research on this topic has just started , napping during night-shift is beneficial to nurses ' health and performance .