Working night shifts is associated with a reduced ability to repair DNA lesions that can, over time, cause DNA damage which could result in mutations known to lead to cancer, research from the US has argued.
The study by the Fred Hutchinson Cancer Research Center, published in Occupational and Environmental Medicine, supported earlier research suggesting night-shift work may be associated with higher cancer risk.
The study by epidemiologist Dr Parveen Bhatti built on 2001 research by Dr Scott Davis, from the same centre, which found that nurses who regularly worked a “graveyard” shift had higher rates of breast cancer.
Other studies have backed up the night shift/cancer connection, leading an International Agency for Research on Cancer study in 2007 that classified shift work as “probably” carcinogenic to humans.
Dr Bhatti measured the presence of a so-called “biomarker” called 8-hydroxydeoxyguanosine (8-OH-dG) in the urine of night-shift workers and then tracked whether these levels changed when the same population reverted to a night-sleep schedule during their days off.
The analysis found that night-shift workers excreted less of the biomarker during periods of work compared to periods of night sleep.
The excreted 8-OH-dG is associated with a lesion created when regular cellular metabolism produces reactive oxygen species, which then react with DNA.
The body normally repairs these 8-OH-dG lesions and excretes the biomarker in urine.
If not repaired, however, the lesions will cause mutations that can eventually lead to cancer.
The fact that night-shift workers excreted less of the biomarker during periods of night work indicated that fewer lesions were being naturally repaired.