We already know that those with cancer are more likely to experience problems with sleep; but poor sleep health may also increase the risk of developing cancer.
A Japanese study involving almost 24,000 women found that those who slept for six hours or less were at a higher risk for breast cancer compared to women who got seven hours of sleep. Researchers found that sleep durations of more than seven hours saw varying results.
Another study in 2010 found that those who get less than six hours of sleep each night had an almost 50 percent increased risk for colon cancer compared to those who get at least seven hours of sleep. (One of the study's authors compared this increase in risk to having a parent or sibling with cancer.)
Additionally, an Icelandic study found that those with severe sleep problems were 70 percent more likely to develop prostate cancer compared to healthy sleepers.
In further worrying news for men, a significant association has been found between increased lung cancer risk and short sleep duration in men between the ages of 42 and 60. Even after adjusting for age, smoking history and family cancer history, after studying data from a population-based cohort of over 2,500 men, researchers found a significant association with increased lung cancer risk.
Perhaps unsurprisingly, lung cancer risk was even higher among current smokers.
Why the association between cancer and poor sleep?
It's thought that sleep problems may alter the balance of two important hormones that influence cancer cells and sleep; cortisol and melatonin.
Typically, cortisol levels rise after waking and fall during the day. For some insomnia sufferers, though, cortisol levels remain at an elevated level, resulting in a continued state of arousal. These higher cortisol levels may also suppress the immune system, which could explain the heightened cancer risk.
Sleep deprivation can also lead to reduced melatonin levels in the body. As well as being an important regulator of our sleep/wake cycle, melatonin is an antioxidant that helps suppress free radicals. It also regulates the production of estrogen which cancer cells need to grow.
What can you do to reduce your risk?
Taking steps to improve sleep should be a priority. This doesn't necessarily require the use of sleeping pills. Good sleep hygiene, sleep restriction and cognitive behavioral therapy can all improve sleep without pills.
It's also important to reduce stress and the associated elevated cortisol levels. This can be done in a number of ways. Yoga and meditation can help, as can exercise.
You can also boost melatonin production by increasing your exposure to light during the day and blocking out as much light as possible at night.