“…Nonetheless, eight of the cross-sectional studies of sleep duration have objectively measured sleep [31,[50][51][52][53][54][55][56] using either actigraphy [50,52,53,55,56] or one night polysomnography (PSG) [31,51,54]. Three of the studies show a negative linear relationship [50,54,56], one shows a U-shaped relationship (however, non-significant after adjusting also for sleep fragmentation) [55], and four studies show no association [31,[51][52][53] between sleep duration and measures of obesity (Table 1).…”