Does poor sleep increase my risk of cancer?
Poor sleep, and sleep apnea and night-shift work in particular, is associated with an increased cancer risk. Whether you personally face a higher risk depends on which sleep problems you have; at the very least, have any apnea symptoms evaluated.
Poor sleep is associated with an increased cancer risk, but this is a correlation, not a proven cause-and-effect chain for every individual sleep problem. Moreover, the relationship also runs in the other direction: cancer itself disrupts sleep, which makes it difficult to distinguish cause from effect.
The clearest signal comes from research into sleep apnea. In people with apnea, oxygen levels drop repeatedly during the night. The total time a person spends with abnormally low oxygen levels is the strongest measurable sleep variable linked to cancer and a more aggressive disease course. The mechanism is thought to involve a protein that cells produce in response to oxygen deprivation, which then drives inflammation and cell growth. The evidence is not yet conclusive and differs by cancer type.
Night-shift work and structural sleep disruption caused by artificial light are best documented in relation to breast cancer. Long-term night-shift work was linked to 50 to 100% more breast cancer in large studies of nurses. The International Agency for Research on Cancer now classifies shift work involving night shifts as 'probably carcinogenic'. The suppression of melatonin likely plays a role here, alongside broader disruptions of the biological clock.
How exactly the biological clock contributes to cancer has also been examined in animal research. Mice in which clock genes were switched off developed faster-growing lung tumors and lived shorter lives. A recent study in mice and cells also suggested that sleep deprivation activates a metabolic pathway that sustains cancer stem cells. Neither finding has yet been confirmed in humans.
For people with ordinary insomnia or irregular sleep, the associations are less clear-cut. The bidirectional relationship makes it difficult to determine how large the independent effect of sleep quality actually is. Getting good sleep has well-established health benefits regardless, but the precise relationship with specific cancer types requires further research.
This answer is based on several review articles and two individual studies. The evidence for sleep apnea and night-shift work is the strongest: it comes from large population studies that followed people for many years. The evidence for biological mechanisms (clock genes, fatty acid metabolism) comes largely from animal experiments and cell culture studies, and has not yet been confirmed in humans to a comparable degree. In all cases these are associations; no single study can establish cause and effect with certainty here. The researchers themselves are cautious: the specific links between individual sleep disorders and specific cancer types have not yet been sufficiently mapped.
Does working at night increase my risk of cancer?
Night work probably increases the risk of breast cancer, and possibly of other types of cancer. If you have been working night shifts for years, it is worthwhile to discuss this with your doctor and to stay alert to population screening programmes.
Does sitting a lot increase my risk of cancer, even if I exercise?
Sitting a lot increases your risk of certain cancers, even if you exercise. In addition to moving regularly, try to reduce your sitting time itself, because the two only partially compensate for each other.
Does being overweight increase my risk of cancer, and if so, which types?
Excess weight increases your risk of at least 13 types of cancer, including uterine, colorectal, breast and liver cancer. Losing weight reduces that risk, although it remains unclear whether all methods of weight loss are equally effective for immune defence against cancer.
Does eating a lot of sugar increase my risk of cancer?
Drinking large amounts of sugary drinks is associated with a noticeably higher risk of certain cancers, especially early-onset bowel cancer and liver cancer. The link is associative, but consistent enough to make cutting back on soft drinks and fruit juice a concrete priority.
What can I do myself to lower my risk of cancer?
By not smoking, limiting alcohol, maintaining a healthy weight, and moving enough, you can meaningfully lower your risk of several common cancers, even if cancer runs in your family.
Does passive smoking (secondhand smoke) increase your risk of cancer?
Passive smoking increases your risk of cancer, with the strongest evidence for lung cancer. The risk is real but smaller than with active smoking; avoiding exposure as much as possible is advisable.