How sleeping too little can increase your cancer risk

If insomnia is as familiar to you as the ceiling you stare up at every night, here's some bad news: Cancer. Yes, other than the gamut of diseases the lack of sleep has been linked to – including heart disease, high blood pressure, diabetes, obesity and depression – you also have to contend with the Big C.

A 2022 YouGov study on more than 1,000 Singapore residents found that 73 per cent are getting less than seven hours sleep per night and over 30 per cent of them only got five to six hours of shuteye. This is well below the global average and a 44-per-cent rise since 2018.

And Singaporeans still aren’t getting enough sleep. According to ResMed’s latest global sleep survey, including over 1,000 Singapore residents, eight in 10 respondents reported one or more symptoms of sleep disruption related to sleep quality. The most common cause of interrupted sleep was obstructive sleep apnoea (81 per cent).

HOW ARE SLEEP AND CANCER LINKED?

Whether your chronic lack of sleep is caused by obstructive sleep apnoea, insomnia or stress, it doesn’t bode well.

In a study published in the journal Cancer, those who slept less than six hours nightly had a 41-per-cent higher risk of cancer than those who slept six to eight hours per night. And if you need a good reason to nap, how does warding off cancer sound? Individuals who did not nap had a 60-per-cent higher risk of cancer than those who snuck in a snooze for more than an hour a day.

The researchers also found that participants who slept less than seven hours in total had a 69-per-cent higher risk of cancer than those who slept seven to eight hours total per day.

It has to do with your body’s clock or circadian rhythm, which controls sleep and a host of other important functions, said psychiatrist Dr Wong Sheau Hwa, who runs SH Wong Sleep & Psychological Wellness Clinic at Mount Elizabeth Medical Centre.

Poor sleep disrupts your circadian rhythm, he said, which can increase your body’s production of stress hormones and cause oxidative stress that damages tissues and cells. It then kickstarts a chain reaction that can lead to chronic inflammation and eventually, create a conducive environment for cancer cells to develop and grow. However, the relationship between chronic poor sleep and cancer is “complex” and “not fully understood yet”, he said.

“Sleep is the period when cellular DNA repairs occur and disruptions may lead to the accumulation of genetic mutations, which promotes cancer development,” said Dr Wong. “In addition, poor sleep also leads to impaired immunity as the immune system becomes less able to detect and eliminate cancerous cells.”

There are also those who work the night shift, which is another concern as the “exposure to light while working overnight shifts for several years may reduce levels of melatonin, encouraging cancer to grow”, according to Johns Hopkins Medicine.

WHAT ARE THE CANCERS INVOLVED?

Cancers of the breast, colon, ovaries and prostate, according to Johns Hopkins Medicine. Liver and lung cancers may also be added to the cancer and sleep deprivation list. In a 10-year Taiwanese study on over 63,000 patients, it was found that the risks of liver and lung cancers were elevated among those with sleep disorders that aren’t linked to sleep apnoea.

Another study discovered that exposure to light at night may increase the risk of breast cancer.

"Much of the research on sleep and breast cancer risk is related to shift work and factors related to disrupted sleep patterns, such as the unexpected light exposure at night," said Professor Charlie Zhong, the principal scientist of epidemiology research at American Cancer Society.

However, he added a caveat: "While it does appear that the light from mobile devices can disrupt sleep, these technologies and how we use them change so quickly that it has been difficult to study when it comes to longer-term health effects, such as cancer".

Dr Wong has seen patients who suffered from different cancers such as cancers of the colon, breast, prostate, lung and pancreas in his sleep clinic. “The prevalence would depend on how common some of these cancers are,” he said.

WOULD SLEEPING IN ON WEEKENDS HELP? HOW ELSE CAN YOU REDUCE YOUR RISK?

No such luck. “This is an unknown but in my opinion, it does not help,” said Dr Wong. “Our human body runs on a 24-hour cycle regulated by the circadian rhythm, with specific physiological processes occurring at certain period of the 24-hour day.

“Sleep makes up a significant portion of this and hence, any disruption during the usual sleep period, will interfere with the specific processes occurring during that time.”

But what if you can’t quit your shift work? Are there other ways to lessen your risk of cancer? Besides sleep, diet and exercise are the other pillars of health to look into, said Dr See Hui Ti, a senior consultant, with Parkway Cancer Centre’s Medical Oncology department.

For instance, eating a healthy and balanced diet can reduce the risk of cancer, noted Cancer Research UK. But the benefit isn’t from any singular cancer-fighting "superfood" that advertisements may have led you to believe. “Your overall diet (what you usually eat in a normal week) is more important than individual foods when it comes to cancer,” noted its website.

As for exercise, physical activity is associated with a lower risk for several types of cancer, including breast, prostate, colon, endometrium and possibly, pancreatic cancer, according to American Cancer Society. Physical activity can help regulate some hormones that contribute to the development of cancer and help keep the immune system healthy.

WHAT ABOUT THE OPPOSITE? CAN SLEEPING TOO MUCH AFFECT CANCER RISKS, TOO?

There is a study that noted too much sleep may actually increase your risk of colorectal cancer. However, Dr Wong isn’t too convinced by that headline. “How sleeping too much can increase cancer risk is not fully understood,” he said.

“The study mentioned that the observations are inconclusive and more specific investigation may be necessary. Studies of this nature actually do not assess the cause-and-effect relationships but make observations on the associations.”

Dr Wong explained that there may be “confounders in the analyses”. For example, the involved patients may have been affected by undiagnosed cancers, which may have caused non-specific symptoms such as fatigue, which then results in longer sleep. “One possible theory for this may be that sleeping too much can lead to disturbances in metabolism and hormonal physiology, which may lead to chronic inflammation.”