 Sleep is vital to one's health and well being. It has been implicated that loss of sleep can directly affect the immune system and increase the risk of various cancers. The immune and hormonal systems communication seems to be a key factor in preventing cancer cells from dividing beyond the immune system's ability to keep them in check. Melatonin and cortisol are two of the most important hormones in preventing cancer. When these hormones are balanced, the risk of cancer and the rate of its progression can be reduced. It has been estimated that up to 88 percent of cancer patients are affected by sleep disorders. Sleep apnea is more common in those with cancer than the general public and cancer patients are twice as likely to experience insomnia. A patient's immune system can be impaired by restless nights from sleep disorders. According to researchers at the University of Texas MD Anderson Cancer Center , sleep apnea has been shown to have a strong correlation with death from cancer. Researchers found that almost 30 percent of patients reporting cancer-related fatigue were diagnosed with sleep apnea and 60 percent were diagnosed with insomnia. Researchers at Stanford and the University of Louisville School of Medicine showed that a patient's circadian rhythm may influence cancer progression. The circadian rhythm is the night and day cycle affecting metabolism, physiology and hormonal production. Melatonin and cortisol Melatonin increases during sleep and has anti-oxidant properties. With an altered circadian rhythm, the body produces less melatonin and the cell's DNA may be more susceptible to cancer-causing mutations. Melatonin has another key role in slowing the ovaries' production of estrogen. For those with breast and ovarian tumors, estrogen stimulates the cancerous cells to continue dividing. Another influential hormone is cortisol, which is high in the morning and declines throughout the day. Cortisol has a regulating factor on immune system activity, including natural-killer cells which destroy cancer cells. The Stanford study found that people who are at high risk for breast cancer have an altered cortisol rhythm, meaning those with a shifted cortisol cycle may be more cancer susceptible. It was also found that women with breast cancer who had their cortisol cycle disrupted, with peak levels in the afternoon rather than at dawn, died earlier from the disease and slept more poorly. Melatonin has also been shown to reduce the growth of prostate cancer. According to a study in the journal Cancer, Epidemiology, Biomarkers and Prevention , results showed that men who had trouble sleeping were twice as likely to develop prostate cancer compared to those who slept well. The correlation was even stronger for cases of advanced prostate cancer and the risk increased relative to the severity of the sleep problems. The study implied that sleep may become a potential target for intervention to reduce the risk of prostate cancer. Approximately 15-20 percent of employees in the USA work an overnight shift. This timing of work can lead to circadian disruption including melatonin synthesis. Studies have shown a potential link between exposure to light at night and risk of breast cancer. Having proper melatonin and cortisol levels has a major impact on sleep. When these hormones are in the normal range they can help improve quality and quantity of sleep. These levels should be tested to screen for potential hormone and immune imbalances so they can be corrected before cancer has a chance to get a foothold. This should be a foundation of any alternative cancer treatment protocol. 