Reply: “Obstructive Sleep Apnea, Sleep Duration, and Fasting Glucose” and “The Impact of Obesity on the Association between Obstructive Sleep Apnea and Glucose Metabolism”

Abstract

The Impact of Obesity on the Association between Obstructive Sleep Apnea and Glucose MetabolismTo the Editor:It was with great interest that I read the article by Bakker and colleagues (1), which concluded that obstructive sleep apnea (OSA) is independently associated with glucose metabolism and that this association may vary by ethnicity. It is well known that OSA in nonobese individuals is significantly associated with impaired glucose metabolism; however, OSA is not associated with abnormal glucose tolerance categories (2). That is to say, the association of OSA with glucose metabolism is different between obese and nonobese individuals. In the study by Bakker and colleagues (1), the differences in the association of OSA with glucose metabolism between obese and nonobese individuals were ignored. As in the study by Bakker and colleagues (1), some individuals with OSA are not obese, especially those of Asian descent (3). Therefore, further studies should be performed to confirm the differences of the association of OSA with glucose metabolism between obese and nonobese individuals and whether this association could vary by ethnicity. n Dr. Kawada expresses concern about our use of actigraphy to quantify habitual sleep duration (1). We did use the medium threshold (40 counts per epoch) to differentiate wake from sleep. Prior studies have not found clear benefits in terms of agreement with polysomnography by using either a higher or lower threshold in adults (2, 3). Although actigraphy is known to underestimate wake after sleep onset as a result of scoring of quiet wakefulness as sleep, there is little evidence to suggest this offset leads to systematic bias. In particular, a prior study found similar performance of actigraphy in quantifying sleep in those with and without sleep apnea (4). Dr. Kawada is also concerned by our categorization of sleep duration. The decision to define short sleep duration as <5 hours/night was made to parallel the categorizations used in prior cohort studies; in particular, the Sleep Heart Health Study (5) and the Nurses' Health Study (6). In addition to these categorical analyses, we assessed the effect of sleep duration as a continuous measure modeled both in a linear fashion and with a quadratic term to allow for a U-shaped relationship. The results from these models were consistent with those from the categorical model presented.Dr. Kawada contrasts our findings with the recent report by Twedt and colleagues of an association between short sleep duration and hyperglycemia in a cohort of women with gestational diabetes (7). We believe their findings are in line with our work, which also found an association between short sleep and abnormal fasting glucose. This association weakened after accounting for sleep apnea severity. As we note, it is unclear whether this reflects confounding or a loss of statistical power. The effect of sleep apnea on the short sleep/glycemia relationship CORRESPONDENCE 580