Is Working At Night Healthy? Late Shifts May Increase Risk of Cancer And Lead to Poor Health

A study adds evidence that night shift work can contribute to poor health outcomes. Reuters

A reverse work schedule—clocking in the hours at night and sleeping when nine-to-fivers of the world are wide awake—may have a long-term detrimental impact on health. According to a new study published Monday in Occupational and Environmental Medicine, a BMJ Journal publication, night shift work can hinder the body's ability to take out cellular "trash" and repair damaged DNA. The result over time is an accumulation of cellular garbage and the formation of cellular lesions that can increase cancer risk and may contribute to other poor health outcomes.

A growing body of research has already explored the potentially carcinogenic effect of night shift work. Much of that research has focused on the impact of late night work on breast cancer risk. But these studies have brought mixed results, and methodologies used suggests many of the findings are not entirely reliable. Some previous studies used self-reported questionnaires that asked women about their work history. But because people often make errors when it comes to answering questions about their past lifestyle more research is definitely needed. Additionally, studies have identified a link between night shift work and other fatal chronic health conditions.

"There's just a lot of complexity there to be able to accurately assess that exposure," says Dr. Parveen Bhatti, an epidemiologist at the Fred Hutchinson Cancer Research Center and lead author on the new study. "That's why, rather than looking at cancer as an end point, we're looking at an intermediate marker."

Bhatti conducted a study based on 50 shift workers that measured a specific biomarker known as 8-hydroxydeoxyguanosine (8-OH-dG), which is associated with the development of lesions when regular cellular metabolism produces oxidation, which reacts with DNA. "In most cases the cellular repair machine will cut out of the damage and it will be excreted from your urine," he says.

However, Bhatti observed night shift workers appear to expel much less of the product. Overall, night shift workers had much lower levels of 8-OH-dG in urine compared to people who worked daytime shifts. The researchers found that on average urinary 8-OH-dG levels in people who worked night shifts were only 20 percent of those observed who worked regular daytime shifts. Bhatti says this biomarker, in particular, is also linked to increased risk for cardiovascular disease, suggesting this might be a pathway linked to a variety of negative health outcomes.

Bhatti's study shows that melatonin, the hormone produced by the pineal gland that regulates the sleep-wake cycle, plays a critical role in this cellular process. His team measured melatonin levels as well and found a clear association between lower levels of the hormone and less 8-OH-dG in urine. Next, Bhatti hopes to explore whether over-the-counter melatonin supplements could help counteract some of the negative health effects of late shift work.