It is hard to live without a good night’s sleep. However, 22% of the people in industrialised countries do that regularly, when they work in shifts, including those during the night. Working in different shifts disrupts the body’s circadian rhythm—a natural process in our body that regulates the sleep-wake cycle. Studies show that about 15% of those who work during shifts are unable to adapt to the changes occurring in their bodies due to the irregular working hours. Although it is known that altered sleep patterns can lead to cardiovascular diseases, obesity, diabetes, dyslipidemia and other conditions, the specifics are not well-studied.
In a first-of-its-kind study, researchers from the University College of Medical Sciences (University of Delhi) & GTB Hospital, Delhi, have explored how working during night shifts on a long-term alters the metabolism of postprandial triglycerides and its effect on increasing the risk of cardiovascular diseases. The findings were published in the journal Experimental Physiology, and the study was funded partly by the Indian Council of Medical Research.
Triglycerides are the end-result of fat metabolism in our body and are the lowest forms of fats that can be stored. They also play a role in causing cardiovascular diseases. The fat molecules that are converted into triglycerides during the night after a meal are called postprandial triglycerides.
Previous studies have shown that under experimental conditions, changes in sleep and work timings also result in altered glucose secretion after meals. Besides, it is known that altered metabolism of postprandial triglycerides results in insulin resistance—a condition where cells in the body become unresponsive to insulin, thus affecting the metabolism of fat and glucose. This condition leads to higher levels of fat in the blood, increasing the risk of developing cardiovascular diseases.
The current study examined the changes in fat metabolism, after an overnight fasting period of 12 hours, between two groups of 20 individuals each. These men and women, aged between 20 and 40 years, were healthy and free from liver diseases, endocrine diseases affecting lipids, diabetes, hypertension and sleep disorders. The first group consisted of healthcare professionals who had not worked in night shifts in the past year or ever, whereas the second had people who worked rotating night shifts, at least four nights per week, for the past year.
The results showed no significant difference in the physical measurements, glucose and lipid levels in the blood, between those who worked in shifts and those who did not. However, there seemed to be a link between the levels of postprandial triglycerides and insulin resistance among those who worked in shifts.
“The findings of this pilot study suggest that rotational night shift duties in healthcare workers might have a negative impact on metabolic parameters, including postprandial triglyceride responses and insulin sensitivity”, say the researchers.
The study also explains the molecular mechanisms behind this finding. Certain enzymes in our body, involved in the metabolism of postprandial lipids, are activated as a response to the body’s sleep-wake cycle or the circadian rhythm. Specific genes further monitor these enzymes. When the circadian rhythm is altered, these genes also change during and immediately after working in night shifts. The researchers observed that these changes reverted to normalcy after a few days, showing the ability of these genes to repair themselves.
So, do findings convincingly suggest that working at night could lead to conditions like diabetes?
“This was a cross‐sectional study that was preliminary in nature and attempted to ascertain whether there is an association between the rotational shift duties of healthcare workers and postprandial triglycerides. Hence, no conclusion on cause and effect can be drawn from the present study”, warn the researchers, adding that further large-scale studies are required to ascertain these aspects.