Peak At Science: 2023 January 3

Peak At Science 20230103
Open Access

Peak At Science: 2023 January 3

Bedtime and evening light exposure influence circadian timing in preschool-age children: A field study

Light exposure and sleep timing are two factors that influence inter-individual variability in the timing of the human circadian clock. The aim of this study was to quantify the degree to which evening light exposure predicts variance in circadian timing over and above bedtime alone in preschool children. Participants were 21 children ages 4.5–5.0 years (4.7 ± 0.2 years; 9 females). Children followed their typical sleep schedules for 4 days during which time they wore a wrist actigraph to assess sleep timing and a pendant light meter to measure minute-by-minute illuminance levels in lux. On the 5th day, children participated in an in-home dim-light melatonin onset (DLMO) assessment. Light exposure in the 2 h before bedtime was averaged and aggregated across the 4 nights preceding the DLMO assessment. Mean DLMO and bedtime were 19:22 ± 01:04 and 20:07 ± 00:46, respectively. Average evening light exposure was 710.1 ± 1418.2 lux. Children with later bedtimes (lights-off time) had more delayed melatonin onset times (r=0.61, p=0.002). Evening light exposure was not independently associated with DLMO (r=0.32, p=0.08); however, a partial correlation between evening light exposure and DLMO when controlling for bedtime yielded a positive correlation (r=0.46, p=0.02). Bedtime explained 37.3% of the variance in the timing of DLMO, and evening light exposure accounted for an additional 13.3% of the variance. These findings represent an important step in understanding factors that influence circadian phase in preschool-age children and have implications for understanding a modifiable pathway that may underlie late sleep timing and the development of evening settling problems in early childhood.



光照射と睡眠タイミングは、ヒトの概日時計のタイミングの個人間変動に影響を与える2つの要因である。本研究の目的は、就学前児童において、夕方の光曝露が就寝時間だけでなく、概日リズムのばらつきをどの程度予測するかを定量的に明らかにすることである。参加者は、4.55.0歳(4.7±0.2歳、女性9名)の子供21名である。子供たちは4日間、通常の睡眠スケジュールに従って行動し、その間、睡眠タイミングを評価するためにリストアクチグラフを装着し、分刻みの照度レベル(ルクス)を測定するためにペンダントライトメーターを装着した。5日目には、家庭での薄明かりによるメラトニン発現(DLMO)評価に参加した。就寝前2時間の光量は、DLMO評価前の4晩の平均値で集計された。DLMOの平均値と就寝時刻はそれぞれ19:22 ± 01:0420:07 ± 00:46であった。夕方の平均光量は710.1 ± 1418.2ルクスであった。就寝時刻(消灯時刻)が遅い子供ほど、メラトニンの発現時刻が遅れていた(r=0.61p=0.002)。夕方の光照射はDLMOと独立して関連していなかったが(r=0.32p=0.08)、夕方の光照射とDLMOの部分相関を就寝時間でコントロールすると、正の相関が得られた(r=0.46p=0.02)。就寝時刻はDLMOのタイミングの分散の37.3%を説明し、夕方の光照射はさらに分散の13.3%を説明した。これらの知見は、就学前児童の概日リズムに影響を与える因子を理解する上で重要なステップであり、幼児期における遅い睡眠タイミングと夕方の定住問題の発症の根底にある、修正可能な経路を理解する上で示唆を与えるものである。

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