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.
Women who routinely work night shifts have a clearly higher risk of breast cancer. A meta-analysis of thirteen studies found a risk increase of approximately 48%. That is considerable, although this figure decreases somewhat when you correct for factors such as number of pregnancies. The effect appears to be greater with more than twenty years of night work, or with short periods involving many consecutive nights.
The suspected mechanism is the suppression of melatonin, a hormone that the pineal gland normally produces at night. Artificial light at night inhibits this production, which disrupts the circadian rhythm. Animal research shows that a disrupted circadian rhythm can accelerate tumour growth. How strongly this mechanism contributes in humans has not yet been precisely established.
For colorectal cancer as a whole, two large cohort studies among nurses (together approximately 190,000 women, followed for up to 24 years) found no elevated risk. One exception is rectal cancer: after fifteen or more years of night shifts, that risk was elevated, by a factor of approximately 1.6. This is a subgroup finding that still warrants confirmation. For prostate and uterine cancer there are epidemiological indications, but causality has not yet been demonstrated.
Cancer does not stand alone. A systematic review of twenty-four studies among nurses found that night work is also associated with sleep problems, diabetes and cardiovascular disease. Anyone weighing the risks of night shifts therefore needs a broader picture than cancer alone.
Evidence for breast cancer: meta-analysis (PMID 16084719) + systematic review (PMID 31132107) + review (PMID 28770538). Colorectal: large cohort studies (PMID 29978466). Mechanism: reviews and not further indexed studies (PMID 18540832, 17973057, 19605423). Animal research lung cancer: PMID 27476975.
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.
Does working with pesticides increase your risk of cancer?
Working with pesticides is associated in multiple studies with an increased risk of several types of cancer, including bladder, bowel, and blood cancers. Avoiding unprotected contact is sensible, especially if you are pregnant or planning to become pregnant.
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 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 alcohol increase your risk of cancer, even with one drink a day?
Yes, even one drink a day increases the risk of certain cancers, particularly breast and colorectal cancer. There is no safe lower threshold; drinking less or stopping reduces your risk immediately.
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.