Previous studies have found that cancer patients who go through group therapy or have a strong social network fare better than those with weaker social support. The question has been how psychosocial factors exert their influence on cancer cells. David Spiegel, MD, the Jack, Lulu and Sam Willson Professor and professor in psychiatry and behavioral sciences, and Sandra Sephton, PhD, a former postdoctoral scholar now at the University of Louisville School of Medicine, suggest that a person's sleep/wake cycle might be the connection.
Spiegel will present this work at the annual American Association for the Advancement of Science meeting at a Feb. 13 session titled "Biology and Behavior: New Pathways to Cancer Control?" "Psychosocial factors affect your behavior patterns, such as exercise, what you eat and drink, and your sleep," Spiegel said. Of these factors, how well you sleep can seriously alter the balance of hormones in your body. This makes the sleep/wake cycle, also called the circadian rhythm, a good candidate for linking a person's social network to his or her cancer prognosis.
Spiegel suggested two possible ways in which the circadian rhythm may influence cancer progression. The first involves a hormone called melatonin, which the brain churns out during sleep. Melatonin belongs to a class of compounds called antioxidants that mop up 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 on duty through the night produce less melatonin and may therefore produce more cancer-activating estrogen, the researchers said.
The second link 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.
One study found that people who are at high risk of breast cancer have a shifted cortisol rhythm, suggesting that people whose cortisol cycle is thrown off by troubled sleep also may be more cancer-prone. In past work, Spiegel and his colleagues have found that women with breast cancer whose normal cortisol cycle is disrupted - with peak levels in the afternoon rather than at dawn - die earlier from the disease. Those women whose cortisol cycle was shifted also tended to sleep poorly, to have lost a spouse or partner and to have cancer-fighting branches of their immune system suppressed.
Other studies back up this theorized connection. Spiegel cited the recent finding that night-shift workers have a higher rate of breast cancer than women who sleep normal hours. What's more, mice whose circadian rhythm has been interrupted show much more rapid tumor growth than normal mice. Together, these studies led Spiegel to suspect that a poor night's sleep may be one link between a weak social network and a poorer cancer prognosis.
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