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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 . . . [Full Text of this Article]

AUTHOR INFORMATION
William T. Donahoo, MD; Robert H. Eckel, MD

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