Reviewer’s report
Title: 
Night-shift work duration and breast cancer risk: an updated systematic
review and meta-analysis
Version: 
1 
Date: 
10 Nov 2020
Reviewer's report:
The authors have attempted to provide a meta-analysis of studies on the effect of
shift work on incidence of breast cancer. 
However, the criteria for diagnosis of
breast cancer are not presented or discussed. 
An extraordinary number of
reference were found, mainly in the Google search, but the total number reported
on in the study was less than 0.005% of the total. 
An explanation for how so
many articles were eliminated is needed. 
Within those 24 studies chosen for
inclusion in the analysis were those "working hours at night at least now and
then." 
Nurses were considered night shift workers if they worked in hospitals.
Other studies included persons who worked at least one year full-time in night
time hours. 
Rotating shifts studies were included along with studies of consistent
night work. The range of conditions leads to high I2 values. 
It is difficult to draw
any conclusions because the studies are so varied. 
The Discussion of previous
meta-analyses of nigh shift work and breast cancer, including sections on case-
control studies and cohort studies is very detailed but does not contribute to our
understanding or interpretation of the present manuscript. 
This part of the
Discussion would more appropriately be included in a review article. 
The section
of the Discussion starting on line 303 which includes some strengths and
limitations is appropriate although the statement on line 303 "the evidence was
supplemented from recent epidemiological studies not covered by the previous
meta-analysis" is confusing. 
What do you mean by supplemented?
Some corrections of the text are needed.
Line 37: Add the word "The" to International Agency
Line 37: Add the word "the" to regarding the relationship
Line 54: Add the word "an" to the phrase "but an increase was not observed
Line 54: Change observe to observed
Line 55: Change "works" to "workers"
Line 248: Change "increased" to "increase"
Line 225: The reference "Ernen et al (2008)" should be given an reference
number
Line 339: Replace the phrase "but increase did not observe in the long-term
night-shift works." with "but an increase was not observed in the long-term
night-shift workers"
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