How well you sleep can seriously alter the balance of hormones in your body. This can disrupt the sleep/wake cycle, also called the circadian rhythm. A disrupted circadian rhythm may influence cancer progression through shifts in hormones like melatonin, which the brain makes during sleep.
Melatonin belongs to a class of compounds called antioxidants, which suppress damaging free-radical compounds. With a disrupted circadian rhythm, the body produces less melatonin and the cell's DNA may be more prone to cancer-causing mutations. Melatonin also slows the ovaries' production of estrogen. For many ovarian and breast tumors, estrogen spurs the cancerous cells to continue dividing. Shift workers who work through the night and produce less melatonin may therefore produce more cancer-activating estrogen.
This is one of the reasons why it is important to sleep in total darkness to decrease the risk of cancer. A second link from the disrupted circadian rhythm lies with a hormone called cortisol, which normally reaches peak levels at dawn then declines throughout the day. Cortisol is one of many hormones that help regulate immune system activity, including the activity of a group of immune cells called natural-killer cells that help the body battle cancer.
The study did not go into yet a third mechanism that may be related to yet another hormone, insulin. University of Chicago researchers have repeatedly shown that insufficient sleep will result in an increased rate of diabetes due to increased insulin resistance, and insulin has been clearly linked to cancer in previous studies. We all know that sleep is important. The research is quite clear that insufficient rest will result in increased rates of cancer and diabetes, but one of the most important reasons you will want to optimize your sleep is to slow down the aging process. If you need some help in this area you can review the sleep guidelines that seem to help many of our patients.
Brain Behavior Immunology October 2003;17(5):321-8