Disturbances of Hormonal Circadian Rhythms by Light Pollution

Abstract

The circadian rhythms evolved to anticipate and cope with cyclic changes in environmental conditions. This adaptive function is currently compromised by increasing levels of artificial light at night (ALAN), which can represent a risk for the development of diseases of civilisation. The causal links are not completely understood, and this featured review focuses on the chronodisruption of the neuroendocrine control of physiology and behaviour by dim ALAN. The published data indicate that low levels of ALAN (2–5 lux) can attenuate the molecular mechanisms generating circadian rhythms in the central oscillator, eliminate the rhythmic changes in dominant hormonal signals, such as melatonin, testosterone and vasopressin, and interfere with the circadian rhythm of the dominant glucocorticoid corticosterone in rodents. These changes are associated with a disturbed daily pattern of metabolic changes and behavioural rhythms in activity and food and water intake. The increasing levels of ALAN require the identification of the pathways mediating possible negative consequences on health to design effective mitigation strategies to eliminate or minimise the effects of light pollution.

Outdoor artificial light at night exposure and gestational diabetes mellitus: a case–control study

“…Secondly, hormonal changes may play a significant role. ALAN exposure may influence hormone levels in pregnant women ( 44 ), particularly melatonin, a hormone crucial for regulating circadian rhythms during pregnancy ( 45 ). ALAN exposure might suppress melatonin secretion, potentially affecting maternal physiology and fetal development negatively.…”

Endocrine–circadian interactions in birds: implications when nights are no longer dark

“…Among the vast physiological effects of light pollution, many affect rhythmic features or arise from circadian or seasonal disruption, as laid out in recent overview articles [12][13][14][15]21,24,28]. A slate of studies, reviewed therein, have elaborated important general features of physiological responsiveness.…”

“…As an interface between clocks and the environment, hormones also mediate many effects of artificial light at night (ALAN) on organisms [12][13][14][15]. The focus of this review is on the major circadian hormone, melatonin, which is highly sensitive to light [16].…”

“…Here, we seek to exemplify the endocrine-clock interface from environmental and physiological perspectives for birds, and then summarize evidence for implications of ALAN exposure. For more comprehensive and detailed coverage of ALAN effects, we refer readers to excellent published reviews [12][13][14][15]21,23,24,28].…”

“…However, other hormones involved in temporal coordination can also be affected by light pollution (see below). For example, in wild species, changes in rhythmic patterns have been demonstrated for corticosteroids and their receptors, and for reproductive hormones and their receptors [ 12 , 15 , 18 , 19 ]. Evidence for ALAN-induced endocrine disruption for a wider range of hormones derives mostly from laboratory rodents [ 20 ].…”