Does poor sleep increase my risk of cancer?
Poor sleep, and certainly untreated sleep apnoea, is associated with an increased cancer risk, but it has not yet been proven that sleeping poorly causes cancer. Have sleep apnoea checked if you have symptoms, and try to maintain a regular sleep schedule.
Poor sleep is indeed associated with an increased cancer risk, but the relationship is complex and far from straightforward. Sleep disorders can promote cancer, yet cancer in turn also causes sleep problems. That makes it difficult to disentangle cause and effect.
The most concrete risk comes from research into sleep apnoea: people whose oxygen saturation regularly drops below 90% face the highest risk of adverse cancer outcomes. This association is not equally strong for all cancer types; for some types no elevated risk has been found, while for others the risk actually appears to fall. Whether treating sleep apnoea reduces cancer risk has not yet been proven.
A disrupted circadian rhythm, such as in people who regularly work night shifts, has been linked to cancer development in both epidemiological and animal research. The biological mechanisms researchers point to are: disruption of the immune system, less effective repair of DNA damage, and dysregulated hormone balance. Scientists in a review published in Science explicitly warned that the available data are still insufficient to conclude that a disrupted circadian rhythm is generally carcinogenic in humans.
Fragmented sleep (in which you wake frequently) may increase the chance of malignant cell growth through the sympathetic nervous system and a less active immune system. This has, however, been demonstrated mainly in mouse studies; in humans the evidence is limited so far. There are also early indications from a cell and patient study that sleep deprivation can create a favourable growth environment for cancer cells in the lung by dysregulating certain genes within the cell, but this mechanism has not been confirmed in larger studies.
A further indirect route may run through the gut microbiome: a disrupted circadian rhythm can alter the composition of gut bacteria and promote inflammation, which in turn can drive cancer. This causal pathway has not yet been proven in humans either.
All sources are reviews, with no randomised trials or meta-analyses. The evidence is predominantly associative; causality in humans has been made plausible only for some mechanisms.
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 sugar-sweetened beverages is associated with a noticeably higher risk of certain cancers, particularly early-onset colorectal cancer and liver cancer. The association is observational, but consistent enough to make reducing soft drinks and fruit juice a concrete point of attention.
What can I do myself to lower my risk of cancer?
By not smoking, limiting alcohol, maintaining a healthy weight and exercising enough, you can demonstrably 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.