What you may have heard
A disrupted sleep cycle reduces our body’s ability to function properly and decreases its ability to ward off cancer (Shafi et al.).
What science tells us
The World Health Organization (WHO) states that circadian disruption alone is a risk factor for cancer.
“Circadian disruption” is defined as any change in sleep pattern, whether it is loss of sleep, difficulty falling asleep, or waking up during the sleep cycle. The body’s central clock is found in the brain and gets its cues largely from light. Presence of light tells our bodies that it is time to be awake, alert, and hungry. The body sets its clock on a 24-hour cycle (based on how much light it senses) and each organ system follows. Our circadian rhythm controls when we wake up, our appetite, our body temperature, and our mood.
Epidemiological Evidence
People who experience jet lag, travel across multiple time zones, do shift work, have sleep disruption, or are exposed to light at night may be at an increased risk of cancers of the prostate, breast, colon, liver, pancreas, ovary, and lung (Shafi et al.). The International Agency for Research on Cancer (IARC), which categorizes cancer risk factors on a scale from cancer-causing (carcinogenic) to not carcinogenic to humans, states that night shift work alone is likely carcinogenic to humans (IARC).
Laboratory Evidence/ Supportive Evidence
Some animal models have been used in laboratory experiments to examine the relationship between lack of sleep and cancer rates. The results also support the conclusions found in human studies: that lack of sleep has complex effects on cancer biology(Yaacoby-Bianu & Hakim).
IARC Carcinogen Classification:
Not classified.
How to reduce your risk
Sleep disruption and other cancer risk factors often appear together, such as workplace or social/life stressors, smoking, high alcohol consumption, poor diet, low physical activity, and obesity. Reducing these stressors and behaviors may decrease your chances of developing cancer.
The Centers for Disease Control (CDC) recommends regular health checkups and telling your doctor if you have any of the following symptoms: severe fatigue or sleepiness when you need to be awake, trouble with sleep or stomach, irritability, poor work performance (frequent mistakes, injuries, etc.), or unexplained weight gain or loss (CDC). In addition, try healthy behaviors to fight the effects of circadian rhythm disruption: get enough sleep, eat a nutritious diet, exercise regularly, avoid tobacco, and limit alcohol drinking (CDC).
The National Institute for Occupational Safety and Health (NIOSH) has a wide range of occupation-specific resources to help employers and workers better cope with the demands of shift work and long hours (NIOSH).
Bottom line
Circadian disruption is high among people who experience jet lag, travel across multiple time zones, work on overnight shifts, or are exposed to light at night. This population may have an increased risk of cancers of the prostate, breast, colon, liver, pancreas, ovary, and lung (Shafi et al.). It is important to talk with a health provider if you have sleep disruption and to seek resources to improve your quality of sleep.
