It makes us fall asleep, hungry at breakfast time and alert during the day, but research also suggests circadian rhythm balance is crucial for other reasons — our 'body clock' could be the key to living a life free of diseases such as skin cancer.
Circadian disruption has been linked to an increased risk of certain types of cancer, including skin cancers such as melanoma. So, let's look at how to keep our circadian clock ticking along for good health.
What is a circadian rhythm?
Circadian rhythm is essentially the body's internal clock. A time-keeping system that has evolved over billions of years, it is the body's natural process of regulating physiological, behavioural and metabolic processes. These processes include things such as the sleep–wake, feeding–fasting and activity–rest cycles, body temperature regulation and hormone secretion. All living things, including humans, are influenced by environmental cues, primarily the light–dark cycle, over a 24-hour period.
The circadian rhythm is primarily controlled by a part of the brain called the suprachiasmatic nucleus (SCN), which is located in the hypothalamus. Considered the body's central clock, it receives information from light-sensitive cells in the eyes. However, other subordinate clocks that exist in tissues elsewhere in the body, such as the liver, skin and heart, synchronise with the 'master clock'. The SCN then orchestrates various physiological and behavioural processes, such as hormone secretion.
Circadian rhythm and cancer risk
A disrupted circadian rhythm has been found to enhance a person's risk of cancer. This is because the circadian clock is critical to the functioning of the typical features of cancer, such as metabolic alteration, DNA repair, cell death and cell proliferation.
However, scientists do not yet fully understand how the disruption promotes cancer development, so gaining a deeper understanding could help to prevent, treat and manage the disease in the future.
The link between disrupted sleep and cancer
Sleep disturbances can lead to irregularities in circadian rhythms and affect various physiological processes. While the occasional disrupted sleep is unlikely to have an impact on a person's risk of developing cancer, it is possible for long-term dysregulation to affect a person's overall well-being. Some of the ways in which disrupted sleep is linked to an elevated cancer risk include:
- It can suppress the hormone which regulates the sleep–wake pattern, called melatonin.
- Chronic sleep deprivation can increase levels of cortisol, a stress hormone.
- It can weaken the immune response and make it more difficult for the body to detect abnormal cells.
- It can trigger inflammation and oxidative stress in the body.
- It affects cell proliferation and DNA repair.
- It leads to metabolic changes, including insulin resistance.
The role of melatonin
The production of the hormone which regulates the sleep–wake cycle, melatonin, is influenced by the circadian rhythm. When the circadian rhythm is disrupted, melatonin production is suppressed, leading to an increased cancer risk. Activities that can disrupt melatonin production, leading to lower levels, include working at night, jet lag, exposure to artificial light at night, or using screens before bed.
In the future, melatonin could also be a helpful cancer treatment, such is its importance to our bodies. Studies on the effect of melatonin on tumour growth show that it reduces growth and cell proliferation. It has also been shown to prevent tumour development.
What does this link with cancer mean for shift workers?
Several studies have concluded that night shift workers have a higher risk of developing certain types of cancer. This is because long-term circadian rhythm disruptions can lead to imbalances in hormones such as melatonin. As discussed above, a lack of melatonin has been linked to an increased cancer risk.
Circadian clock dysfunction may also affect the body's ability to repair DNA, lead to insufficient sleep, which can weaken the immune system, and disrupt the normal variations of hormones, such as cortisol and growth hormone.
Circadian rhythm and skin cancer
Skin cancer, predominately caused by exposure to UV light, is one of the most common forms of cancer. Just as the suprachiasmatic nucleus communicates with internal organs, the skin is also under circadian control.
Shift work, specifically at night when the circadian rhythm is disrupted, has been associated with an increased risk of some skin cancers but not others. One study found that circadian rhythm disruptions increased the risk of melanoma but decreased the risk of basal cell carcinoma and had no impact on the likelihood of developing squamous cell carcinoma.
Lifestyle strategies for circadian health
Our modern society can make it difficult to maintain healthy circadian clock function, but it's important as a part of a healthy lifestyle to optimise circadian rhythms to reduce your risk of developing cancer.
Whether you're a shift worker or have difficulty sleeping, it's critical to have strategies to help you maintain a regular sleep schedule. Follow these approaches to strengthen your circadian function.
- Make sure you're exposed to natural light during the day.
- Minimise exposure to artificial light at night.
- Make your bedroom a screen-free zone.
- Keep a regular meal schedule.
- Get regular physical activity.
- Limit your intake of caffeine, alcohol and nicotine.
Time check-ups to keep your body clock healthy
While the connection between circadian rhythm and skin cancer has been clearly established, more research is required to understand how our internal body clock impacts cancer progression and how it could be used in treatments and therapies in the future.
Establishing lifestyle practices that support healthy body clock function and reducing other cancer risk factors, such as smoking and unprotected sun exposure, can help mitigate the risk of developing skin cancer.