Goulet Geneviève, Mongrain Valérie, Desrosiers Catherine, Paquet Jean, Dumont Marie
Chronobiology Laboratory, Sacré-Coeur Hospital of Montréal, Department of Psychology, Université de Montréal, Québec, Canada.
J Biol Rhythms. 2007 Apr;22(2):151-8. doi: 10.1177/0748730406297780.
Morning-type individuals (M-types) have earlier sleep schedules than do evening types (E-types) and therefore differ in their exposure to the external light-dark cycle. M-types and E-types usually differ in their endogenous circadian phase as well, but whether this is the cause or the consequence of the difference in light exposure remains controversial. In this study, ambulatory monitoring was used to measure 24-h light exposure in M-type and E-type subjects for 7 consecutive days. The circadian phase of each subject was then estimated in the laboratory using the dim-light melatonin onset in saliva (DLMO) and the core body temperature minimum (Tmin). On average, M-types had earlier sleep schedules and earlier circadian phases than E-types. They also showed more minutes of daily bright light exposure (> 1000 lux) than E-types. As expected, the 24-h patterns of light exposure analyzed in relation to clock time indicated that M-types were exposed to more light in the morning than E-types and that the reverse was true in the late evening. However, there was no significant difference when the light profiles were analyzed in relation to circadian phase, suggesting that, on average, the circadian pacemaker of both M-types and E-types was similarly entrained to the light-dark cycle they usually experience. Some M-types and E-types had different sleep schedules but similar circadian phases. These subjects also had identical light profiles in relation to their circadian phase. By contrast, M-types and E-types with very early or very late circadian phases showed large differences in their profiles of light exposure in relation to their circadian phase. This observation suggests that in these individuals, early or late circadian phases are related to relatively short and long circadian periods and that a phase-delaying profile of light exposure in M-types and a phase-advancing profile in E-types are necessary to ensure a stable entrainment to the 24-h day.
早起型个体（M型）的睡眠时间表比晚睡型个体（E型）更早，因此他们暴露于外部明暗周期的情况也有所不同。M型和E型个体的内源性昼夜节律相位通常也存在差异，但这是光照暴露差异的原因还是结果仍存在争议。在本研究中，采用动态监测连续7天测量M型和E型受试者的24小时光照暴露情况。然后在实验室中使用唾液中褪黑素开始分泌的暗光时间（DLMO）和核心体温最低点（Tmin）来估计每个受试者的昼夜节律相位。平均而言，M型个体的睡眠时间表和昼夜节律相位比E型个体更早。他们每天暴露于强光（>1000勒克斯）下的时间也比E型个体更多。正如预期的那样，根据时钟时间分析的24小时光照模式表明，M型个体在早晨比E型个体暴露于更多的光，而在傍晚则相反。然而，当根据昼夜节律相位分析光照分布时，没有发现显著差异，这表明平均而言，M型和E型个体的昼夜节律起搏器对他们通常经历的明暗周期的同步方式相似。一些M型和E型个体有不同的睡眠时间表，但昼夜节律相位相似。这些受试者在昼夜节律相位方面的光照分布也相同。相比之下，昼夜节律相位非常早或非常晚的M型和E型个体在昼夜节律相位方面的光照分布存在很大差异。这一观察结果表明，在这些个体中，昼夜节律相位早或晚与相对较短和较长的昼夜周期有关，并且M型个体的光照暴露延迟分布和E型个体的光照暴露提前分布对于确保与24小时昼夜的稳定同步是必要的。
