Impact of circadian clock dysfunction on human health

Abstract

All living organisms exhibit circadian rhythms. Humans show circadian rhythm of the different physiological functions such as sleep-wake cycle, core body temperature, feeding behavior, metabolic activity, heart rate variability, hormone secretion, and others. The hypothalamic suprachiasmatic nucleus (SCN) acts as a primary circadian pacemaker. Peripheral tissues have an endogenous circadian clock; however, SCN synchronizes the circadian activity of the peripheral clocks. The retinohypothalamic tract (RHT) from retinal ganglionic cells carries the photic signal into the SCN that regulates the rhythmic expression of the core clock genes through the feedback loop. At the output level, the SCN connects with the pineal gland and the peripheral tissues with the help of neuroendocrine mediators. Disruption of circadian clock functions is detrimental to health. Shift work, night work, chronic or acute jet lag, and light-at-night have adverse effects on circadian functions. Misalignment of circadian rhythm alters the expression of core clock genes, leading to deregulation of cellular activity and metabolic functions. Circadian rhythm dysfunction causes many pathologic conditions, including sleep disorders, cardiovascular problems, metabolic dysfunction, infertility, poor physical performance, as well as cancer. The present work has reviewed the relationship between circadian clock dysfunction and impaired physiological activities.

Missing the Dark: Malediction for the Environment and Human Health

“…Circadian clock dysfunction deregulates different rhythms (melatonin ACTH/cortisol, body temperature), and metabolic activities. Besides these, circadian clock disruption and low levels of melatonin are associated with many health problems, such as sleep disorders, cardiovascular diseases, metabolic disorders, infertility, neurodegenerative diseases, psychiatric problems, and cancers [12]. Lightinduced circadian clock dysfunction decreases alertness, cognitive behavior, mental stability, and physical performance that sometimes increase the probability of accidents at late night in the transportation system, industrial area, and power plants [73].…”

“…According to International Agency for Research on Cancer (IARC) shift work is "carcinogenic to humans (Group 2A)" [82]. Shift work and night work can enhance the risks of breast, ovarian, prostate, colorectal, hepatocellular, and other cancers [11,12]. Although melatonin is associated with several essential functions, the deregulation of melatonin rhythm promotes breast cancer [83,84], ovarian cancer [85], prostate cancer [86], colorectal cancer [87], hepatocellular [88], endometrial cancer [89], and lung cancer [90].…”

“…Desynchronizations of circadian rhythm and melatonin output have negative impacts on human health. Light pollution promotes several health issues including, the disintegration of the sleep-wake cycle, poor physical performance, increased risk of metabolic disorders, neurodegenerative diseases, psychiatric problems, and suppression of melatonin secretion [11,12].Low levels of melatonin decrease antioxidant profiles and increase oxidative stress, and inflammatory response, leading to cardiovascular disease, type II diabetes and induction of various types of cancers (breast, prostate, ovary and others) [13,14]. The present review focuses on the adverse effects of light pollution on the different living systems and their ecological impacts.…”