Shift work, or work that occurs outside the normal 9-5 hours, has been associated with chronic disease and illness including an increased risk of certain cancers, heart disease, obesity, and depression. These negative effects are likely due to a loss of a normal sleep schedule which disrupts the body’s production of melatonin. Melatonin is a hormone produced by the pineal gland (specialized gland in your brain) that helps to regulate your sleep cycles. Melatonin also has an important role as an antioxidant and as a protector of DNA in your cells. Previous studies have linked shift work with elevated levels of oxidative stress which is known to damage DNA and potentially lead to an increase risk for chronic disease. To understand if shift work and sleep disruptions are associated with a loss in the melatonin anti-oxidant mechanism, a team of researchers from Seattle recruited night shift workers and monitored the levels of melatonin and other metabolites in their urine.
The study used urine collected from a total of 223 night shift workers during day or night sleep (on their day off) and 217 day shift workers during their night sleep. Measures of sleep quality, melatonin abundance, and DNA damage marker (8-hydroxydeoxyguanosine or 8-OH-dG) were taken. The data showed that when night shift workers slept during the day they secreted 17-23% less 8-OH-dG than their day shift counter parts or their own night sleep on their day off. There was an increased capacity to secrete 8-OH-dG if the person also had higher levels of melatonin or if their sleep efficiency was better.
In a second recently published paper, the researchers measured these same molecules during the night shift work (when the people were awake) and compared them to normal levels during night sleep. They found that during the night shift work their circulating melatonin levels were 3 times lower than when they were sleeping at night. Additionally, these workers had a 20% reduction in the secretion of 8-OH-dG in their urine during night work than night sleep.
These results suggest that night shift workers have a deficit in their melatonin secretion and anti-oxidant systems during night work or day sleep that limits their ability to repair damaged DNA. The cells DNA is repaired by removing the 8-OH-dG and secreting it in the urine. If this process is unable to proceed then the damaged DNA remains in place and can lead to diseases like cancer. Melatonin has been shown in other studies to directly stimulate DNA repair and so reduced levels in these night shift workers could lead to a loss in the ability to remove 8-OH-dG from the DNA. The study has some limitations including the lack of direct DNA damage measures in the cells of the subjects. A decrease in the secretion of 8-OH-dG could mean a loss of DNA damage repair capacity but it could also indicate a decrease in the amount of DNA damage. The only way to tell would be to directly test the level of DNA damage. As is, this study provides an interesting commentary on the importance of night sleep (and not day sleep) in shift workers and suggests that melatonin supplementation may be a way to control chronic disease in this population of people.
Image Credit: Flickr Kirill ΞΚ Voloshin