Key Features:
- The human body follows a roughly 24-hour circadian cycle
- Environmental cues such as light regulate this 24-hour “clock”
- Circadian disruption is linked to a growing number of diseases
- These include various cancers, neurogenerative diseases and more
Circadian rhythms are the daily variations seen across almost all animals and plants. In the human body, these are biological, physiological, neurological, and behavioral processes and patterns that repeat with a period of roughly 24 hours. Examples include sleep/wake cycle, food intake, core body temperature variation, cellular function, hormone regulation/release, and patterns of gene expression. While these processes are self-sustained, they are adjusted by environmental cues (i.e., zeitgebers or “time-givers”), for example the 24-hour light-dark cycle.
Disruption of circadian rhythms has far reaching impact. Many diseases are either caused or exacerbated by circadian disruption. The evidence is overwhelming that circadian disruption causes harm and reduces quality of life.
There are many causes of cancer. Recently, circadian disruption has been added to this list [1]. Initially, a link between shift work and breast cancer was discovered [2]. Since then, the molecular mechanisms of this issue have been elucidated [3]. The list of cancers now known to be linked to circadian disruption is long. Cancer of the prostate [4], [5], thyroid [6], colon [7], ovary [8], liver [9], lung [10], and skin [11]. It is not just the incidence of developing cancer in the first place that is impacted by circadian disruption. The growth rate of tumors is accelerated by circadian disruption [12]–[14]. Circadian disruption also increases resistance to treatment [13], [14]. This is a triple hit. You are more likely to get cancer, the cancer will be more aggressive, and it will respond less to treatment. This leads to poorer outcomes for more people. However, the picture is not all doom and gloom. Reinforcement and enhancement of circadian rhythms has shown promise as a strategy to control cancer progression [15].
