While studies have long connected fragmented sleep with fatigue and irritability, for the first time, a clinical connection between poor sleep and cancer has been found. A recent study has concluded that poor sleep marked by frequent awakenings can speed a cancer tumor’s growth and increase its aggressiveness. For the study, a pediatric pulmonary and sleep expert spent 2 years at the University of Chicago leading a joint team of researchers from that institution and the University of Louisville. According to their findings, over time, interrupted sleep patterns diminish the body’s ability to fight off cancerous cells, contributing to the malignancy of the disease.

The research team observed 2 sets of mice in the study. Both sets were injected with cancer cells and all began to develop malignant tumors. One set of mice was allowed to sleep normally, while the other set had its sleep patterns repeatedly disrupted. After 4 weeks, researchers found that the tumors in sleep-deprived mice were not only bigger, but more aggressive. The cancerous tumors in the sleep-deprived group were also malignant, invading surrounding muscle and bone tissues.

It’s Not the Tumors

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For years, scientists have known that melatonin has had an immune-enhancing effect. It’s a hormone that’s produced exclusively at night as we sleep. Nocturnal melatonin is an important part of the body’s inherent 24-hour clock—or the circadian rhythm. The circadian rhythm regulates many of our biological processes, including the sleep-wake cycle. It is believed that the sleep-wake cycle, and the melatonin produced as a result of it, plays an important role in regulating hormones that influence cancers, such as breast and prostate cancer.

Higher levels of melatonin may decrease the risk of developing advanced prostate cancer. Researchers in Boston have found that men with higher levels of melatonin have a 75% reduced risk of developing prostate cancer compared with men who have lower levels. According to one expert, “Sleep loss and other factors can influence the amount of melatonin secretion—or block it altogether. Health problems associated with low melatonin, disrupted sleep, and disruption of the circadian rhythm are broad including a potential risk factor for cancer,” says Sarah C. Markt, MPH, Department of Epidemiology at Harvard School of Public Health.

An increase in the risk of breast cancer has also been found among women with lower melatonin levels. As in men, this increased risk comes from not sleeping well during the period of sleep when nocturnal melatonin levels are at their highest. Breast cancer risks were studied in women who worked a late shift for some time during the decade leading up to their breast cancer diagnoses. There was clear evidence of an increased risk in breast cancer associated with lower nocturnal melatonin levels and the number of years a graveyard shift was worked.

The Role of TAMs

In the University of Chicago study, researchers found that the mice whose sleep was disrupted had tumors twice the size of those in the set that slept normally. They also found that the cancerous tumors in the sleep-disrupted mice were not only larger, but more malignant and aggressive than those in the mice that slept normally. When they investigated further, the team discovered that the difference in the 2 groups of mice was being driven by immune cells called tumor-associated macrophages, or TAMs. Depending on what signals they receive, TAMs work in 1 of 2 ways. They either eliminate cancer cells and prevent tumors, or they promote new blood vessel activity and support tumor growth. Researchers found the well-rested mice had mostly TAMs working in the core of their tumors, eliminating cancer cells. However, in the sleep-disrupted mice, the TAMs were located around the edges of the tumors, promoting blood vessel activity and helping the cancers grow.

Far-Reaching Implications

The US Centers for Disease Control and Prevention says that approximately 70 million Americans suffer from chronic sleep problems. A research team is now planning on examining how sleep disruption affects a cancer patient’s response to chemotherapy. People living with cancer can make changes to their daily habits, sleep environment, and stress levels that can make a difference in their quality of sleep. Making note of the time they go to bed, how many times they wake in the night, what disturbs their sleep, and what time they wake up can help patients identify patterns in their sleeping habits. Considering how sleep disruption, like cancer, strikes millions of people every year, these new study results have far-reaching implications.


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