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Our body has a natural biological clock called a circadian rhythm that plays an essential role in regulating and maintaining our wake and sleep cycles, eating cycles and hormonal cycles. The brain region that the master circadian clock resides in is called the suprachiasmatic nuclei (SCN) found on the anterior hypothalamus. This small brain region, comprised of about 10,000 neurons, sits on top of the same pathway involved with vision, giving it the ability to process information regarding light and dark. This circadian clock ends up playing a role in controlling nearly every cell in the body regarding metabolism and gene expression.
Concept check: A simplified explanation of how this small brain region can play such a large role on the body. Since this region can detect light and dark by connecting to your eye pathway, it can tell other brain regions to start releasing a molecule called melatonin that is responsible for slowly turning off your brain for sleep. As your brain slows down, your body starts to use less energy, and each cell in your body begins to go into this “sleep mode”. Your body, from being in this same cyclical pattern every day, “learns” to use specific pathways to stay awake and function normally for about the same time every day. This is because these pathways are time sensitive meaning that depending on the starting time, it will all turn off at roughly the same time.
There is new evidence suggesting that there is a link between a disruption in circadian rhythm and cancer. Many studies regarding cancer rates in populations of people, who have a disruption in circadian rhythm, all point to there being a causal link. Some types of disruption include working night shifts, jet lag and late eating habits. The link is strong enough for the International Agency for Research on Cancer (IARC) to classify working the night shift as a group 2A carcinogen. When you change the way this natural process works, such as by working overnight, the metabolic pathways within the cells gets disrupted, causing slight stress to the cells. If this stress is constant throughout your life, this evidence suggests that it will increase your likelihood of developing cancer. Even eating right before you go to sleep can disrupt your circadian rhythm. A study of 41,400 people from the French NutriNet-Sante cohort found that eating after 9:30 pm, disrupting in normal metabolic cycle, leads to an increased risk of both breast and prostate cancer. A possible explanation could be that when your body is starting to slow down and conserve energy use, eating late forces your body to start back up to process the food. These conflicting signals cause stress to cells, specifically in your circadian pathway. In mice studies, when genes associated with the circadian clock is removed, the probability of the mouse getting cancer is increased significantly. Other studies have shown when mice are put under a jet lag manipulated environment, their circadian rhythm related gene expression was disrupted leading to a significant increase in cancer.
The complex molecular networks between the circadian clock and the development of cancer are just beginning to be understood. Fundamentally, there is strong evidence that lifestyle choices that disrupt the circadian clock are linked with cancer. Further understanding of this pathway could shed light on new perspectives on cancer treatment as well as cancer prevention. The body is comprised of many complicated systems that seem to be more connected than we once thought. By taking care of our body, we can play a small part in reducing the incidences of cancer on a population level.