Relationship between sleep parameters and lipid profile with special reference to the validity of actigraphy.

I read with interest the article by Toyama et al 1 in a recent issue of CHEST (March 2013). They conducted a cross-sectional study to examine the relationship between sleep indicators and lipid profi les in 275 working men. OSA and sleep duration were judged by specifi c devices. Among them, I have some concerns about the device Actiwatch (Philips Respironics) and its ability to determine sleep duration. First, the authors mentioned in the Materials and Methods section that sleep duration was estimated from analysis of actigraphy tracings in conjunction with a sleep diary. Unfortunately, they did not describe procedures, and they cited only one reference for the use of actigraphy to estimate sleep-wake time. 2 There is a review on the usefulness of actigraphy, 3 but systemic discrepancies between actigraphy and EEG-defi ned sleep also exist. For example, subjects generally become inactive in a sleep-induction period, which would relate to the underestimation of sleep-onset latency. 4