Studying communities at different stages of urbanisation and industrialisation can teach us how timing and intensity of light affect the circadian clock under real‐life conditions. We have previously described a strong tendency towards morningness in the Baependi Heart Study, located in a small rural town in Brazil. Here, we tested the hypothesis that this morningness tendency is associated with early circadian phase based on objective measurements (as determined by dim light melatonin onset, DLMO, and activity) and light exposure. We also analysed how well the previously collected chronotype questionnaire data were able to predict these DLMO values. The average DLMO observed in 73 participants (40 female) was 20:03 ± 01:21, SD, with an earlier average onset in men (19:38 ± 01:16) than in women (20:24 ± 01:21; P ≤ .01). However, men presented larger phase angle between DLMO and sleep onset time as measured by actigraphy (4.11 hours vs 3.16 hours; P ≤ .01). Correlational analysis indicated associations between light exposure, activity rhythms and DLMO, such that early DLMO was observed in participants with higher exposure to light, higher activity and earlier light exposure. The strongest significant predictor of DLMO was morningness‐eveningness questionnaire (MEQ) (beta=−0.35, P ≤ .05), followed by age (beta = −0.47, P ≤ .01). Sex, light exposure and variables derived from the Munich chronotype questionnaire were not significant predictors. Our observations demonstrate that both early sleep patterns and earlier circadian phase have been retained in this small rural town in spite of availability of electrification, in contrast to metropolitan postindustrial areas.

中文翻译：

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在农村人口中具有高级活动节律和昏暗的褪黑激素发作的早期睡眠类型。

研究城市化和工业化不同阶段的社区可以教会我们光的时间和强度如何影响现实生活条件下的生物钟。我们之前在位于巴西一个乡村小镇的 Baependi 心脏研究中描述了一种强烈的晨起倾向。在这里，我们基于客观测量（由昏暗的褪黑激素开始、DLMO 和活动确定）和光照，测试了这种早晨倾向与早期昼夜节律相关的假设。我们还分析了之前收集的时间型问卷数据预测这些 DLMO 值的能力。在 73 名参与者（40 名女性）中观察到的平均 DLMO 为 20:03 ± 01:21，SD，男性 (19:38 ± 01:16) 的平均发病时间比女性 (20:24 ± 01:21；磷 ≤ .01)。然而，男性在 DLMO 和睡眠开始时间之间表现出更大的相位角（4.11 小时 vs 3.16 小时；P  ≤ .01）。相关性分析表明光照、活动节律和 DLMO 之间存在关联，因此在暴露于更高光照、更高活动和更早光照的参与者中观察到早期 DLMO。DLMO 的最强显着预测因子是早晚问卷 (MEQ)（β=-0.35，P  ≤ .05），其次是年龄（β = -0.47，P ≤ .01)。来自慕尼黑时间型问卷的性别、光照和变量不是重要的预测因素。我们的观察表明，尽管有电气化，但与大都市后工业区相比，这个乡村小镇保留了早期的睡眠模式和更早的昼夜节律阶段。