Evening chronotype, late weekend sleep times and social jetlag as possible causes of sleep curtailment after maintaining perennial DST: ain’t they as black as they are painted?

People sleep less in response to setting social clocks earlier relative to the sun clocks. We proposed here a model-based approach for estimating sleep loss as the difference between weekend and weekday risetimes divided on the difference between weekend risetime and weekday bedtime. We compared this approach with a traditional approach to estimating sleep curtailment as the difference in weekly average sleep duration in two conditions. Weekday and weekend sleep times reported for 320 samples provided possibility of testing whether evening types with later weekend sleep times and larger social jetlag differ from morning types with earlier weekend sleep times and smaller social jetlag on amount of sleep lost (1) throughout the week and (2) in response to an advance of weekday wakeups, for instance, after the expected installation of perennial Daylight Saving Time (DST). We found that (1) an amount of sleep lost due to advancing shift of weekday wakeups depends upon neither chronotype nor weekend sleep times nor social jetlag, (2) a very large amount of sleep is usually lost by evening types with later weekend sleep times and larger social jetlag and (3) an essential sleep loss is caused by our usual work/school schedules, even in morning types with early weekend sleep times and small social jetlag. As compared to such permanent sleep losses experienced by any types, an additional loss due to switching from Standard Time (ST) to perennial DST are expected to be relatively small. We also found that the traditional way of calculation of sleep curtailment leads to paradoxical conclusions, such as (1) sleep loss is larger when social jetlag is smaller, not larger, (2) sleep loss is larger when weekend sleep times are earlier, not later, (3) despite 1-h difference between two student samples in weekday wakeups, their sleep losses can be identical.

当社会时钟相较于太阳时钟提前调校时，人们的睡眠时间会相应缩短。本研究提出了一种基于模型的睡眠损失估算方法：将周末与工作日起床时间的差值，除以周末起床时间与工作日就寝时间的差值。本研究将该方法与传统睡眠缩减量估算方法进行了对比，传统方法以两种条件下的周平均睡眠时长差值作为估算依据。本研究纳入320份样本报告的工作日与周末睡眠时间数据，以此验证：（1）在整周范围内，（2）在工作日起床时间提前的情况下（例如，预计推行永久夏令时（Daylight Saving Time, DST）后），晚睡型（周末睡眠时间更晚、社交时差（social jetlag）更大）与晨型（周末睡眠时间更早、社交时差更小）人群的睡眠损失量是否存在差异。研究结果显示：（1）因工作日起床时间提前导致的睡眠损失量，与昼夜节律型（chronotype）、周末睡眠时间及社交时差均无关联；（2）晚睡型人群（周末睡眠时间更晚、社交时差更大）通常会出现极为显著的睡眠损失；（3）即便对于晨型人群（周末睡眠时间更早、社交时差更小），日常工作/学业作息也会造成大量的睡眠损失。与各类人群均会面临的这类永久性睡眠损失相比，从标准时（Standard Time, ST）切换至永久夏令时所带来的额外睡眠损失相对较小。本研究同时发现，传统睡眠缩减量计算方法会得出矛盾结论，例如：（1）社交时差越小，睡眠损失反而越大，而非越大；（2）周末睡眠时间越早，睡眠损失反而越大，而非越晚；（3）即便两组学生样本的工作日起床时间相差1小时，二者的睡眠损失量也可能完全一致。