Night shift work has been associated with a variety of adverse health effects. New research adds to these, suggesting that the body's ability to repair DNA damage may be inhibited by night shifts.
Additionally, some studies have indicated that night shifts may increase a person's risk of developing lung cancer and cardiovascular disease.
Now, new research examines how night shifts influence the body's ability to repair its DNA. The first author of the study is Dr. Parveen Bhatti, of the Fred Hutchinson Cancer Research Center in Seattle, Washington.
The findings were published in the journal Occupational & Environmental Medicine.
Building on previous research
In a previous study, Dr. Bhatti and colleagues showed that sleeping during the day correlated with lower levels of 8-hydroxydeoxyguanosine (8-OH-dG), which is a chemical released as a byproduct by the body when it works to repair its own DNA.
The authors were therefore led to believe that these low levels of 8-OH-dG found in the urine may indicate the body's impaired ability to repair its cellular damage.
They also hypothesized that the reduced levels of urinary 8-OH-dG may be due to the fact that our bodies produce less melatonin during day sleep compared with night sleep.
To further explore this idea, Dr. Bhatti and colleagues set out to examine whether night work also correlates with reduced urinary levels of 8-OH-dG.
The authors explain the motivation for their new research, saying, "If excretion of 8-OH-dG during night work among these subjects is also decreased relative to night sleep, it would provide additional support for our hypothesis that reduced melatonin among shift workers is associated with decreased oxidative DNA damage repair capacity."
Night shifts may inhibit DNA repair
Dr. Bhatti and colleagues selected 50 shift workers from the 223 included in their former research.
These shift workers had the widest gap between their levels of circulating melatonin when they were working at night and when they engaged in normal night sleep.
The levels of circulating melatonin were assessed by measuring 6-sulfatoxymelatonin levels in the urine.
To measure 8-OH-dG levels, Dr. Bhatti and colleagues used "high-performance liquid chromatography with electrochemical detection." They then used mixed effects models to compare night work 8-OH-dG levels with night sleep 8-OH-dG levels.
The study found that melatonin levels were drastically lower during night work than during night sleep.
The researchers also adjusted for possible confounders, such as alcohol use and shorter sleep duration during the day before the night shift. After the adjustments, 8-OH-dG levels were 80 percent lower than the levels recorded during night sleep.
"Our results," write the authors, "indicate that, relative to night sleep, reduced melatonin production among shift workers during night work is associated with significantly reduced urinary excretion of 8-OH-dG."
Dr. Bhatti and colleagues also explain what these results mean, saying, "This likely reflects a reduced capacity to repair oxidative DNA damage due to insufficient levels of melatonin and may result in cells harboring higher levels of DNA damage."
"If such effects are confirmed, melatonin supplementation should be explored as an intervention to reduce the occurrence of potentially carcinogenic DNA damage among shift workers."
Furthermore, the authors note that a so-called NER molecular pathway is believed to play a key role in DNA damage repair - and some studies have indicated that the production of melatonin enhances the activity of NER genes.
Limitations of the study include the observational nature of the research, meaning that no conclusions could be drawn on cause and effect. Additionally, the population sample was limited to Caucasian healthcare workers, so it is difficult to generalize the findings to a wider population.