Reviewer's report
Title:Plasma 25-hydroxyvitamin D and risk of premenstrual syndrome in a
prospective cohort study
Version:2Date:24 March 2014
Reviewer: Sunni Mumford
Reviewer's report:
This Review is Completed by Dr. Kerri Kissell, MD, NICHD
The authors provide some thoughtful feedback in regards to the questions raised
by this reviewer, however, I have some remaining questions and comments.
Comment 1 Revisions:
In their response to comment 1, the authors state “In women in who were
diagnosed with PMS prior to providing a blood sample, it is possible that the 25
OH D level we measured does not reflect a level that would be etiologically
related to symptom development.” Regardless of the associations drawn in this
paper, I wonder if the authors can make any assumptions about etiology or
causality.
I am still not convinced in the stability of 25(OH)D over multiple years. The
authors cite a supplementation trial by Mocanu and Vieth (Nutr J 2013; 12:137)
which was performed in nursing home residents, a population that had little, if
any outside exposure, and moreover, all vitamin D supplement was supplied
(and controlled) by trained nursing home staff, thereby decreasing variability
tremendously compared to the study population in this study.
Moreover, the other study cited in the paper now, “Meng JE, Hovey KM,
Wactawski-Wende J, Andrews CA, LaMonte MJ, Horst RL, Genco RJ, Millen
AE1:Intraindividual variation in plasma 25-hydroxyvitamin D measures 5 years
apart among postmenopausal women. Cancer Epidemiol Biomarkers Prev 2012;
21:916-924,” occurred in postmenopausal women. I wonder how this
postmenopausal population would differ in vitamin D stability to the study
population. Perhaps this concept could be explored more in the discussion.
Comment 2 Revisions:
Thoughtful comments: 1. “We selected this assay to maximize comparability with
other recent assays of 25OHD within the Nurses’ Health Study 2 Blood Cohort.
Our assay is primarily a measure of 25(OH)D3, but is also cross-reactive for
25(OH)D2. Cross-reactivity for the two isoforms are 100% (D3) and 75% (D2).” I
feel this should be emphasized in the paper.
2. “vitamin D binding globulin, which emerging data suggest contributes to the
bioavailability of 25OHD. While we were unable to measure VDBG…” Perhaps
this should also be emphasized in the paper, thereby letting readers know the
authors are aware of these issues within the field and potential confounders.
Comment 3 Revisions:
I wonder if the authors of this study found any fault with the statement, “Many
studies over the last decade have shown that corrected calcium is an unreliable
estimator of patients’ calcium status as assessed by ionized calcium. As
demonstrated by Clase et al (Nephrol Dial Transplant 2000; 15:1841-1846), the
correction formula that has been used widely (Payne et al. Br Med J
1973;4:643-646) agrees less well with ionized calcium than the unadjusted total
calcium.”
Clase, in the cited article, still recognized ionized calcium as gold standard and
states that a major limitation to their work (in regards to the corrected calcium
calculation) is the small size of their population in addition to the inclusion and
exclusion criteria limiting any severely low albumin, therefore the utility of the
correction formula could not be adequately assessed.
Perhaps too, I wonder if Toffaletti’s comment was misinterpreted. As Toffaletti
points out: although total calcium may be a reliable “screening test for calcium
abnormalities”, it is not a replacement for ionized calcium. I would recommend
stating clearly in manuscript that ionized Ca was not available and total calcium
was the most reliable AVAILABLE SCREENING tool.
Comment 5 Revisions:
I still am unclear if Bain et al., and Dennis LK et al., were able to demonstrate a
clear positive relationship between number of moles on lower leg and amount of
sun exposure.
Comment 6 Revisions:
Perhaps the authors need to state this as limitation in the discussion.
Comment 7 Revisions:
I wonder how many women would differ in their dose categories between 1991
(or earlier than 1999 time of selection) and 1999? Perhaps to be discussed as
limitation.
Thank you for the summary: “In 1999, calcium and vitamin D supplement use
was measured by food frequency questionnaire. Dose categories for calcium
were none, <400 mg/day, 400-900mg/day, 901-1300mg/day, and #1301 mg/day.
Fifty-six percent of participants reporting calcium supplements reported using
400-900 mg/day, while 28% reported 900-1300 mg/day. Use of vitamin D
supplements was measured as yes/no.” I think the paper would be strengthened
by adding this to methods section.
Perhaps, the authors should relate their findings to the current Institutes of
Medicine guidelines for Vit D deficiency and insufficiency in the discussion.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: Yes, but I do not feel adequately qualified to assess the
statistics.
Declaration of competing interests:
I declare I have no competing interests