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Annual variation in daily light exposure and circadian change of melatonin and cortisol concentrations at a northern latitude with large seasonal differences in photoperiod length
Jönköping University, School of Engineering, JTH, Civil Engineeering and Lighting Science.ORCID iD: 0000-0003-0123-8996
Department of Environmental Science, Fukuoka Women's University, Japan.
Department of Environmental Science, Fukuoka Women's University, Japan.
2016 (English)In: Journal of Physiological Anthropology, ISSN 1880-6791, E-ISSN 1880-6805, Vol. 36, no 1Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Seasonal variations in physiology and behavior have frequently been reported. Light is the major zeitgeber for synchronizing internal circadian rhythms with the external solar day. Non-image forming effects of light radiation, for example, phase resetting of the circadian rhythms, melatonin suppression, and acute alerting effects, depend on several characteristics of the light exposure including intensity, timing and duration, spectral composition and previous light exposure, or light history. The aim of the present study was to report on the natural pattern of diurnal and seasonal light exposure and to examine seasonal variations in the circadian change of melatonin and cortisol concentrations for a group of Swedish office workers.

METHODS: Fifteen subjects participated in a field study that was carried out in the south of Sweden. Ambulatory equipment was used for monthly measurements of the daily exposure to light radiation across the year. The measurements included illuminance and irradiance. The subjects collected saliva samples every 4 h during 1 day of the monthly measuring period.

RESULTS: The results showed that there were large seasonal differences in daily amount of light exposure across the year. Seasonal differences were observed during the time periods 04:00-08:00, 08:00-12:00, 12:00-16:00, 16:00-20:00, and 20:00-24:00. Moreover, there were seasonal differences regarding the exposure pattern. The subjects were to a larger extent exposed to light in the afternoon/evening in the summer. During the winter, spring, and autumn, the subjects received much of the daily light exposure in the morning and early afternoon. Regarding melatonin, a seasonal variation was observed with a larger peak level during the winter and higher levels in the morning at 07:00.

CONCLUSIONS: This study adds to the results from other naturalistic studies by reporting on the diurnal and seasonal light exposure patterns for a group living at a northern latitude of 56° N, with large annual variations in photoperiod length. It seems to be seasonal variation in the lighting conditions, both concerning intensities as well as regarding the pattern of the light exposure to which people living at high latitudes are exposed which may result in seasonal variation in the circadian profile of melatonin.

Place, publisher, year, edition, pages
2016. Vol. 36, no 1
Keywords [en]
Circannual, Cortisol, Light exposure, Melatonin, Northern latitude, Spectral composition, hydrocortisone, adult, circadian rhythm, female, human, male, metabolism, middle aged, photoperiodicity, physiology, season, sunlight, Sweden, time factor, Humans, Photoperiod, Seasons, Time Factors
National Category
Architectural Engineering
Identifiers
URN: urn:nbn:se:hj:diva-43219DOI: 10.1186/s40101-016-0103-9ISI: 000392974100001PubMedID: 27435153Scopus ID: 2-s2.0-85014606166Local ID: GOA JTH 2016; JTHBebyggdISOAI: oai:DiVA.org:hj-43219DiVA, id: diva2:1292526
Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-02-28Bibliographically approved
In thesis
1. Non-image-forming effects of light: Implications for the design of living and working environments
Open this publication in new window or tab >>Non-image-forming effects of light: Implications for the design of living and working environments
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seasonal variation in mood and subjective well-being are common at geographical locations further away from the equator. The 24-h light-dark cycle is the main time cue for synchronizing the human circadian clock to the external day and night.

Nowadays, people spend more of their waking day indoors, with less exposure to the natural daylight cycle, relying on artificial lighting which differs to daylight in a number of aspects, including intensity, spectral composition and light exposure pattern.

In parallel with the technology development that has been mainly driven by energy-saving reasons, it is important to investigate the non-image-forming effects of different properties of the daily and seasonal light exposure.

The overall aim of the thesis was to identify characteristics of the daily light exposure that are important to support physiological and psychological needs of humans. To achieve this objective a number of research questions were posed concerning daily and seasonal light exposure, seasonal variation in physiological processes and psychological parameters, and evaluation of light exposure with respect to non-image-forming effects. The research questions were investigated in a longitudinal research design with measurements conducted each month during the year at a high latitude with large seasonal variation in day lengths.

Self-report diaries and instruments for ambulatory- and static measurements were used to examine daily and seasonal light exposure in the working and living environments and for investigating the relationship between different parameters that can be used for evaluating light exposure according to non-image-forming effects of light. Seasonal variation in daily light exposure and regarding the pattern of light exposure was observed. Also, the results indicate a seasonal variation concerning the quality (i.e. spectral composition of the visible radiation) of the exposing light.

Two biological markers, melatonin and cortisol, were used for investigating seasonal variation in physiological processes relating to the circadian clock. The results showed higher morning melatonin concentrations and peak level of melatonin during the winter although no seasonal change was observed concerning the phase position of the melatonin rhythm.

Seasonal differences in mood and sleep-activity were studied by means of selfreport diaries and questionnaires. Seasonal variations were observed for both parameters. The results showed higher ratings of mood in the summer, particularly 6 in the evening, and a relationship between bedtime and evening light exposure and photoperiod length. Furthermore, longer sleep times was observed in the winter.

Appraisal of lighting conditions in the offices during the year was rated by the use of a questionnaire. The results showed some seasonal differences concerning the perceived qualities of the light and some associations between characteristics of the lit environments and positive affect were found.

Two methods, static- and ambulatory measurements, were used for recording lighting conditions in the working environments. Taken together, the results showed weak associations between the two methods.

Research have demonstrated an increased need for taking non-image-forming effects into consideration when designing working and living environments, especially at geographical locations with large variations in day length where people are exposed to much of the daily light exposure at the workplace. Laboratory research has provided a good understanding of the basic concepts. However, more field research is needed. Also, current research has demonstrated that new methods of measuring and evaluating lighting conditions are needed.

Place, publisher, year, edition, pages
Lund: Department of Architecture and Built Environment, Faculty of Engineering, Lund University, 2018. p. 67
Keywords
circadian rhythms, circannual, light exposure, melatonin, cortisol, sleep-wake behavior, perception, mood, spectral composition, measurement
National Category
Architectural Engineering
Identifiers
urn:nbn:se:hj:diva-43220 (URN)978-91-7740-112-4 (ISBN)978-91-7740-113-1 (ISBN)
Opponent
Supervisors
Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-02-28Bibliographically approved

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