- The presence of free radicals leads to DNA damage that occurs daily, which is considerably repaired during sleep at night.
- Night shift workers disrupt this pattern leading to poor efficiency of the repair mechanism.
- Melatonin levels were found to be associated with poor repair mechanism, with supplementation being a potential form of therapy.
The advent of technology has made it possible to work from across the globe, which has led to large numbers of people working during the night. Apart from such technology-based work, there are other jobs that necessitate work to be carried out during the night, like health care workers or security personnel; all jobs that require working at night affect the circadian rhythm.
The change in the circadian rhythm could affect the body's natural ability to repair DNA damage
that is caused by normal functions of the body. This study brings to the fore the ill effect of working during the night and it is detailed in the journal Occupational & Environmental Medicine.
Circadian rhythm is the pattern of sleeping at night when it is dark, and then remaining awake during most parts of the day when there is sunshine or brightness.
This is a natural part of the life of humans as well as animals. Scientists who studied the circadian rhythm found that this alternating pattern of sleeping and waking was associated with the presence of darkness and daylight.
‘A good night’s rest is necessary to lower risk of sustained DNA damage and promote repair.’
The main aspect of sleep is governed by the extent of exposure to light or darkness.
When there is light, the nerve pathway is stimulated from the retina of the eye to the hypothalamus of the brain. The suprachiasmatic nucleus
(SCN) in the brain signals to the regions of the brain that are involved in regulating hormones, body temperature as well as other body functions that are associated with the state of wakefulness or sleep.
The SCN functions similar to a clock, which is why it is called an internal body clock, setting off a pattern of tasks that have an effect on the whole body. When the first rays of the sun or light of the day reach the body, the SCN starts carrying out functions that increase the temperature of the body while prompting the release of hormones like cortisol. This region of the brain is also found to suppress the release of melatonin,
the hormone which is associated with inducing sleep, till many hours later or till darkness sets in.
Melatonin is a hormone secreted by the pineal gland,
a pea-sized gland present near the mid brain region. The pineal gland remains inactive during the day but when the sun sets and there is darkness, this gland is activated and begins synthesizing melatonin. This is normally expected to occur around 9 p.m., around which time the level of melatonin is found to peak. There is reduction in alertness of the brain. The levels of melatonin remain high for nearly 12 hours, coinciding with night, and they drop around daytime. Melatonin levels are very low during the day.
The scientists involved in the study showed that the inability to repair the DNA damage could be associated with the suppression of melatonin, a hormone that is known to regulate the internal body clock.
The scientists involved in the study found in an earlier research study conducted by them that there was a lower level of a chemical formed as a by-product of DNA tissue repair (8-OH-dG)
on night shift workers who slept during the day. This study was conducted on 223 night shift workers and the level of 8-OH-dG,
the marker of DNA tissue repair, determined. The lower levels of the DNA tissue repair marker indicated that there was reduced DNA tissue repair. The scientists hypothesized that the major factors that lead to the reduced amount of DNA tissue repair could be suppression of melatonin.
Comparing DNA Tissue Repair Marker
In the current study the research team analyzed whether the level of 8-OH-dG might be lower among night shift workers when compared to people who work during the day and rest at night. The 8-OH-dG levels were measured from stored urine samples of 50 night shift workers, collected during the earlier study.
The findings of the study were:
- The level of melatonin was a lot lower among night shift workers when they worked during the night than when they had a normal night's sleep.
- Even after controlling for confounding factors like consumption of alcohol and shorter sleep during the day (5.5 hours), the level of 8-OH-dG was only 20% of the level that was found after a normal night's sleep (7.5 hours of sleep)
DNA damage, caused by free radicals, is repaired via a pathway called NER. According to the research team, the hormone melatonin is found to enhance the activity of genes associated with the NER pathway. Therefore, lowered melatonin levels affect the body's ability to repair DNA damage.
Though this is an observational study, and the study participants were white males, which limits association with a multi-racial population, the initial findings do signify a potential health risk associated with altering the circadian rhythm.
The study highlights the need to focus on the health of night shift workers, many of whom are emergency workers and who will not be able to alter their work timings, like health workers or security personnel. Further studies could examine the level of anti-oxidants in the blood and could be used to recommend appropriate anti-oxidant intake to lower DNA damage due to free radicals.
The reduced production of melatonin among night shift workers
was found to be associated with reduced level of urinary levels of 8-OH-dG,
signifying the importance of a good night's sleep. This finding can be used to encourage better sleeping habits at night, especially among adults who are habitual late sleepers due to poor lifestyle choices like watching television and other entertainment factors.
The accumulation of DNA damage over a period of time could increase the risk for diseases like cancer. Hence the researchers suggest effective interventional strategies like supplementation with melatonin,
which could help night shift workers improve their DNA repair mechanism.
- Parveen Bhatti, Dana K Mirick, Timothy W Randolph, Jicheng Gong, Diana Taibi Buchanan, Junfeng (Jim) Zhang, Scott Davis. Oxidative DNA damage during night shift work. Occupational and Environmental Medicine, (2017); oemed-2017-104414 DOI: 10.1136/oemed-2017-104414
- Melatonin and Sleep - (https://sleepfoundation.org/sleep-topics/melatonin-and-sleep)