Aging is associated with sleep and circadian alterations, which can negatively affect quality of life and longevity. Importantly, the age-related reduction in light sensitivity, particularly in the short-wavelength range, may underlie sleep and circadian alterations in older people. While evidence suggests that non-image-forming (NIF) light responses may diminish in older individuals, most laboratory studies have low sample sizes, use non-ecological light settings (e.g., monochromatic light), and typically focus on melatonin suppression by light. Here, we investigated whether NIF light effects on endogenous melatonin levels and sleep frontal slow-wave activity (primary outcomes), and subjective sleepiness and sustained attention (secondary outcomes) attenuate with aging. We conducted a stringently controlled within-subject study with 3 laboratory protocols separated by ~ 1 week in 31 young (18–30 years; 15 women) and 16 older individuals (55–80 years; eight women). Each protocol included 2 h of evening exposure to commercially available blue-enriched polychromatic light (6500 K) or non-blue-enriched light (3000 K or 2500 K) at low levels (~ 40 lx, habitual in evening indoor settings). Aging significantly affected the influence of light on endogenous melatonin levels, subjective sleepiness, sustained attention, and frontal slow-wave activity (interaction: P < 0.001, P = 0.004, P = 0.007, P = 0.001, respectively). In young individuals, light exposure at 6500 K significantly attenuated the increase in endogenous melatonin levels, improved subjective sleepiness and sustained attention performance, and decreased frontal slow-wave activity in the beginning of sleep. Conversely, older individuals did not exhibit signficant differential light sensitivity effects. Our findings provide evidence for an association of aging and reduced light sensitivity, with ramifications to sleep, cognition, and circadian health in older people.
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We thank Dr. Julia Krebs, Dr. Thomas Götz, and Dr. Corrado Garbazza for medical screenings, Dr. Christina Schmidt for assistance with the cognitive data preprocessing, Giovanni Balestreri, Claudia Renz, Marie-France Dattler, and all the study helpers for their help in data acquisition. We thank Dr. Roland Steiner, Dr. Dieter Lang, and Prof. Peter Oelhafen for their assistance with the light settings, and the volunteers for participating in this study.
This study was financially supported by the AXA Foundation (https://www.axa-research.org/en/project/christian-cajochen) and by the Swiss Federal Office for Public Health (Consumer Protection Directorate, 11.007647). The funders had no role in the design and conduct of the study; collection, management, analyses, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Ethical approval and consent to participate
Our study complied with ethical standards. All study participants provided written informed consent. The local Ethical Committee (EKBB/Ethikkommission beider Basel, Switzerland) approved the study protocol, advertisements, screening questionnaires, and the consent form, which were in agreement with the Declaration of Helsinki.
Consent to participate
All study participants provided written informed consent. The local Ethical Committee (EKBB/Ethikkommission beider Basel, Switzerland) approved the study protocol, advertisements, screening questionnaires, and the consent form, which were in agreement with the Declaration of Helsinki.
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All co-authors have reviewed the content provided in the article and consent for publication.
Conflict of interest
C.C. has had the following commercial interests related to lighting: honoraria, travel, accommodation and/or meals for invited keynote lectures, conference presentations or teaching from Toshiba Materials, Velux, Firalux, Lighting Europe, Electrosuisse, Novartis, Roche, Elite, Servier, and WIR Bank. C.C. is a member of the Daylight Academy. None of these are related to the current study and manuscript publication. S.L.C., V.B., and S.F. declare that they have no competing interests.
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Chellappa, S.L., Bromundt, V., Frey, S. et al. Age-related neuroendocrine and alerting responses to light. GeroScience (2021). https://doi.org/10.1007/s11357-021-00333-1
- Light sensitivity
- Circadian photosensitivity