A study of human adaptability to regional light conditions

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This study was performed from a viewpoint of the human adaptation to environment under the light in different seasons and regions. The daily activity, sleep factors, melatonin rhythms, and lighting conditions (illuminance and wavelength) the participants received in daily life were compared between 4 seasons ( spring, summer, autumn and winter) and 3 regions (Fukuoka/Japan, Poznan/Poland and Hanoi/Vietnam). In Japan, the clear seasonal variation was seen in melatonin rhythm. The peak value of melatonin secretion was higher and the peak time of melatonin secretion seems delay in autumn as compared with other seasons. The seasonal variations of melatonin secretion were not seen in Poland and Vietnam. There were significant differences in peak value and peak time of melatonin secretion among 3 regions. Moreover, there were seasonal variations and regional differences in light conditions the participants received.This research showed that the human melatonin rhythm has seasonal and regional variation. This is one of the proofs human being has adapted and evolved under natural environment. Therefore, when our living environment becomes more artificial from now on, it is anxious that those artificial environments have serious influences on human biological rhythms. In the case of the design for future living environment, we need to consider the conditions of the artificial environment where human can be healthy and live comfortably with human adaptation ability to environment.