We read with interest the study by Ockene et al1 evaluating the seasonal variation in serum lipid levels. This study is important in that it highlights a significant variation in lipid levels that occurs seasonally, and this variation does not appear to be associated with changes in diet or activity. However, there are several limitations in study design that restrict their conclusions. The authors attribute the change in lipid levels to changes in plasma volume. This assumption is fraught with difficulties and is not consistent with either their data or other published data. The measure of plasma volume using hemoglobin levels is not only imprecise,2 but relationships between estimates of change in hemoglobin level and plasma volume and serum lipid levels are never examined. Moreover, assessment of the data fails to incorporate potential seasonal changes in other hormones such as erythropoietin that could also explain the changes seen in hemoglobin level. Other hormones have been reported to vary seasonally, and hemoglobin A1c level is 0.4% lower in the summer than in the winter, a measure not related to hemodilution.3 In addition, in our small study,4 we found significant correlations between changes in lipoprotein lipase activity and changes in high-density lipoprotein cholesterol and triglyceride levels. The lipoprotein lipase activity is a bioassay done ex vivo, and the activity is expressed per gram of tissue or adipocyte cell size. This measure is not altered by changes in hemodilution and yet can explain some of the seasonal changes in serum lipid levels in a physiological way.
Thank you for submitting a comment on this article. It will be reviewed by JAMA Internal Medicine editors. You will be notified when your comment has been published. Comments should not exceed 500 words of text and 10 references.
Do not submit personal medical questions or information that could identify a specific patient, questions about a particular case, or general inquiries to an author. Only content that has not been published, posted, or submitted elsewhere should be submitted. By submitting this Comment, you and any coauthors transfer copyright to the journal if your Comment is posted.
* = Required Field
Disclosure of Any Conflicts of Interest*
Indicate all relevant conflicts of interest of each author below, including all relevant financial interests, activities, and relationships within the past 3 years including, but not limited to, employment, affiliation, grants or funding, consultancies, honoraria or payment, speakers’ bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued. If all authors have none, check "No potential conflicts or relevant financial interests" in the box below. Please also indicate any funding received in support of this work. The information will be posted with your response.
Some tools below are only available to our subscribers or users with an online account.
Download citation file:
Web of Science® Times Cited: 1
Customize your page view by dragging & repositioning the boxes below.
More Listings atJAMACareerCenter.com >
Enter your username and email address. We'll send you a link to reset your password.
Enter your username and email address. We'll send instructions on how to reset your password to the email address we have on record.
Athens and Shibboleth are access management services that provide single sign-on to protected resources. They replace the multiple user names and passwords necessary to access subscription-based content with a single user name and password that can be entered once per session. It operates independently of a user's location or IP address. If your institution uses Athens or Shibboleth authentication, please contact your site administrator to receive your user name and password.