More than 238,000 men are diagnosed with prostate cancer in the United States each year, according to the American Cancer Society. Approximately one in six men will be diagnosed with the disease at some point in their lifetime. What if the quality of sleep plays a role in a man's risk for developing the disease?
That's the question posed by a new study examining the link between prostate cancer and disrupted sleep. It's just the latest in a wave of research in recent years that has discovered links between poor sleep and several types of cancer. The results of the latest study suggest that men who have trouble falling asleep and staying asleep -- two common symptoms of insomnia -- may be at twice the risk of developing prostate cancer.
Researchers from the University of Iceland in Reykjavik followed 2,102 men over a period of five years. The men were all part of a large public-health study in Iceland that included more than 2,000 men between the ages 67-96. None of the men had prostate cancer at the time the study began. At the study's outset, researchers asked all the men four questions related to their sleep:
- Did they take medication to help them sleep?
- Did they have trouble falling asleep?
- Did they wake up in the night and have difficulty returning to sleep?
- Did they wake up early in the morning and have trouble falling back asleep?
After observing the men for five years, and adjusting for factors such as age, researchers found that poor sleep was associated with elevated risk for prostate cancer:
- 8.7 percent of men reported experiencing severe sleep problems
- 5.7 percent of men reported sleep problems classified as "very severe"
- During the five-year study period, 6.4 percent of men were diagnosed with prostate cancer.
- Difficulty falling asleep and staying asleep was associated with an increased risk for prostate cancer. Men with trouble falling asleep and staying asleep were between 1.7 to 2.1 times as likely to develop prostate cancer as those without these sleep problems
- Among men with advanced prostate cancer, the link with disrupted sleep was even stronger. Men with "very severe" sleep problems demonstrated as high as 3.2 times the risk of developing prostate cancer as those who did not experience sleep problems
This study adds to the growing body of research showing evidence of a relationship between poor sleep and risk for prostate cancer and other types of cancer. No direct, causal link has been established between sleep problems and the onset of cancer. But several studies in recent years have shown strong associations between risk levels for cancer and poor, insufficient, and disrupted sleep:
- A team of researchers at Harvard University investigated the relationship between sleep duration, snoring, and risk of colorectal cancer. Using data from the Health Professionals Follow Up Study and the Nurses' Health Study, researchers included in their study more than 30,000 men and 70,000 women between ages 40-73. They found that longer sleep duration -- sleeping nine or more hours per night -- was linked to increased risk of colorectal cancer in people who are overweight and who snore regularly. As these are symptoms of obstructive sleep apnea, these results raise the question whether the effects of sleep-disrupted breathing might be a factor in cancer risk.
- Researchers at Case Western Reserve University also studied sleep and the risk of colorectal cancer. They found that people who averaged less than six hours of sleep per night had a 50 percent higher risk of colorectal cancer, compared to those who slept at least seven hours nightly. Participants who developed colorectal cancer were also more likely to report having been diagnosed with sleep apnea, and were more likely to have participated in shift work.
- Several studies have shown links between disrupted sleep and increased risk of breast cancer. A number of these studies used women participating in shift work, which frequently results in overnight work shifts and changing sleep schedules. Shift work puts people at high risk for disrupted sleep, sleep disorders, and a range of health problems.
- Researchers in Japan examined the risk of prostate cancer among shift workers, and found an elevated risk among certain shift workers. Researchers observed more than 14,000 working men in Japan, and found that those who worked rotating shifts were three times as likely to develop prostate cancer as day workers. Men who worked fixed-schedule night shifts showed a very small increase to their risk of developing prostate cancer.
We're still at the early stages of understanding just how significant a role sleep may play as a risk factor in the development of cancer. This is an important area of study that could have a significant impact on prevention and screening, and perhaps even treatment of the disease. The prospect of a connection between sleep and cancer risk is yet another very important reason to maintain healthy sleep habits.
Michael J. Breus, PhD
The Sleep Doctor®
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