Suppression of men's responses to seasonal changes in day length by modern artificial lighting

Abstract

We recently reported that humans have conserved mechanisms, like those that exist in other animals, which detect changes in day length and make corresponding adjustments in the duration of nocturnal periods of secretion of melatonin and of other functions. We detected these responses in individuals who were exposed to artificial "days" of different durations. The purpose of the present study was to determine whether men who are exposed to natural and artificial light in an urban environment at 39 degrees N are still able to detect and respond to seasonal changes in duration of the natural photoperiod. We measured profiles of circadian rhythms during 24-h periods of constant darkness (< 1 lx) and found no summer-winter differences in durations of nocturnal periods of active secretion of melatonin, rising levels of cortisol, high levels of thyrotropin, and low levels of rectal temperature. The results of this and our previous study suggest that modern men's use of artificial light suppresses responses to seasonal changes in the natural photoperiod that might otherwise occur at this latitude.

Evidence for a biological dawn and dusk in the human circadian timing system

“…On these occasions, the average times (± S.D.) of sunrise and sunset were 07.19 ± 00.10 h and 17.06 ± 00.18 h in winter and 05.51 ± 00.07 h and 20.33 ± 00.04 h in summer, respectively (for details see Wehr et al 1995a). …”

“…Their compliance was monitored with sleep logs. Volunteers participated in five different studies, the details of which have been published elsewhere (Wehr et al 1993(Wehr et al , 1995aWehr, 1996;Aeschbach et al 1997Aeschbach et al , 1999. All research was consistent with the Declaration of Helsinki and was approved by the institutional review board of the Intramural Research Program of the National Institute of Mental Health (NIMH).…”

“…3. Data are extracted from Wehr et al (1995a). measurement periods were identical in the two conditions, data from the two conditions were averaged for each subject to reduce variance arising from measurement error and biological variability.…”

Neel revisited: the adipocyte, seasonality and type 2 diabetes

“…Substantial interest has developed in the general effects of disruption of this rhythmicity on health in man [40,41]. Human responses to seasonal changes in the natural photoperiod were more robust prior to the Industrial Revolution and have subsequently been increasingly suppressed by alterations in the physical environment [42,43]. Disruption of these processes is exemplified by the extreme circumstances of reversal of day/night working patterns seen in some shift workers.…”

Is there an evolutionary mismatch between the normal physiology of the human dopaminergic system and current environmental conditions in industrialized countries?

“…Several studies from Wehr and collaborators 62 have suggested that modern men's use of artificial light after dark and artificial darkness during the daytime suppresses responses 63 to seasonal changes in the duration of the natural scoto-and photoperiod that might otherwise occur at a given latitude, producing a chronic disturbance in the sleep pattern and decreasing, overall, the total amount of sleep. It is difficult to conceive that chronic sleep deprivation in humans could be obtained and maintained without any activation in the stress axis.…”