Brighter nights and darker days predict higher mortality risk: A prospective analysis of personal light exposure in >88,000 individuals.
Light enhances or disrupts circadian rhythms, depending on the timing of exposure. Circadian disruption contributes to poor health outcomes that increase mortality risk. Whether personal light exposure predicts mortality risk has not been established. We therefore investigated whether personal day and night light, and light patterns that disrupt circadian rhythms, predicted mortality risk. UK Biobank participants (N = 88,905, 62.4 ± 7.8 y, 57% female) wore light sensors for 1 wk. Day and night light exposures were defined by factor analysis of 24-h light profiles. A computational model of the human circadian pacemaker was applied to model circadian amplitude and phase from light data. Cause-specific mortality was recorded in 3,750 participants across a mean (±SD) follow-up period of 8.0 ± 1.0 y. Individuals with brighter day light had incrementally lower all-cause mortality risk (adjusted-HR ranges: 0.84 to 0.90 [50 to 70th light exposure percentiles], 0.74 to 0.84 [70 to 90th], and 0.66 to 0.83 [90 to 100th]), and those with brighter night light had incrementally higher all-cause mortality risk (aHR ranges: 1.15 to 1.18 [70 to 90th], and 1.21 to 1.34 [90 to 100th]), compared to individuals in darker environments (0 to 50th percentiles). Individuals with lower circadian amplitude (aHR range: 0.90 to 0.96 per SD), earlier circadian phase (aHR range: 1.16 to 1.30), or later circadian phase (aHR range: 1.13 to 1.20) had higher all-cause mortality risks. Day light, night light, and circadian amplitude predicted cardiometabolic mortality, with larger hazard ratios than for mortality by other causes. Findings were robust to adjustment for age, sex, ethnicity, photoperiod, and sociodemographic and lifestyle factors. Minimizing night light, maximizing day light, and keeping regular light-dark patterns that enhance circadian rhythms may promote cardiometabolic health and longevity.
Windred 2024（PNAS, n=88,905）は同じグループによる光環境研究。1週間の光センサーデータと8年追跡で、夜の光が明るい人は全死因死亡15〜34%増、昼の光が明るい人は16〜34%減という鮮やかな結果。
これは「サーカディアン健康」を行動レベルで変えるエビデンスとして強い。寝室の暗さ、朝のカーテン全開、日中の屋外光——これらが寿命に直結する。スマホのスタンバイLED、テレビの常夜灯、街灯の漏れ光まで、累積で効いてくる。
私自身は寝室を完全遮光にし、朝の外来前にデスクで強い光を浴びる位置に座っている。出張先でも遮光カーテンの隙間にタオルを詰めるくらい徹底する。「夜は暗く、昼は明るく」は健康習慣として再評価されるべき。