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设置时，人们的睡眠时间会相应缩短。本文提出了一种基于模型的睡眠损失估算方法：以周末与工作日起床时间之差，除以周末起床时间与工作日就寝时间之差。我们将该方法与传统睡眠缩减量估算方法进行了对比，传统方法以两种情境下的周平均睡眠时长之差作为估算依据。针对320份样本报告的工作日与周末睡眠时间，我们得以检验两类问题：一是在整周范围内，二是在工作日起床时间提前（例如，在永久夏令时（Daylight Saving Time, DST）预期推行后）的情境下，周末睡眠时间更晚、社交时差（social jetlag）更大的夜型人群（evening chronotype），与周末睡眠时间更早、社交时差更小的晨型人群（morning chronotype），其睡眠损失量是否存在差异。研究结果显示：其一，因工作日起床时间提前而产生的睡眠损失量，既与个体的睡眠时型无关，也不受周末睡眠时间及社交时差的影响；其二，周末睡眠时间更晚、社交时差更大的夜型人群，通常会经历大幅的睡眠损失；其三，即便是周末睡眠时间更早、社交时差更小的晨型人群，日常的工作/学业作息也会造成显著的睡眠损失。与各类人群均会经历的此类持续性睡眠损失相比，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。此外我们还发现，传统的睡眠缩减量计算方法会得出自相矛盾的结论，例如：（1）当社交时差更小时，睡眠损失反而更大，而非社交时差更大时；（2）当周末睡眠时间更早时，睡眠损失反而更大，而非更晚时；（3）即便两份学生样本的工作日起床时间存在1小时差异，二者的睡眠损失量却可能完全相同。