Misalignments of modern life give rise to “social jet lag”

New habits are changing our biological clock and making people more nocturnal. Researcher warns that the phenomenon is causing part of the population to experience one time zone for weekdays and another for weekends.

By Maria Fernanda Ziegler, in New York  |  Agência FAPESP – In modern societies, daily rhythms – those that cause us to wake up, feel hungry or become sleepy – are determined by three clocks: the sun clock, the internal clock and the social clock. The latter is viewed as an imposition that causes us to wake up hours before we would like to in order to go to work, and creating what is known as “social jet lag.”

This finding is by Orie Shafer, a chronobiologist and neurobiologist at the City University of New York (CUNY), who credits this misalignment with serious health and emotional issues all over the world.

“We need to have an interdisciplinary and international understanding of this issue. We believe this misalignment occurs all over the world and that it is having an impact on people’s health and productivity as well as on economies and schools. Social jet lag is related to insomnia and other phenomena that include stimulant abuse and depression, for example,” said Shafer in a talk given at FAPESP Week New York, held November 26-28, 2018.

Shafer’s laboratory at the Advanced Science Research Center of CUNY is focused on understanding how neuron networks promote circadian rhythm – biochemical mechanisms that allows human beings to organize their sleep and wake times over the 24-hour daily cycle.

Shafer, however, is particularly interested in understanding how the neuron networks of the internal clock operate when challenged by artificial light, a lack of sunlight and darkness.

Research into the internal clock are generally conducted on fruit flies (Drosophila melanogaster), the model animal that presents similarities to humans with regard to studying the genes and neurons that control the internal clock.

“There are 20,000 neurons in each hemisphere of the brain. The Drosofila offers an excellent model, with 1,000 neurons, only 70 of which contain the molecular clock. The genes discovered in fruit flies are similar to those discovered in humans and the mutations in these corresponding regions of the brain cause sleep changes in humans,” he said.

Discovery of the molecular mechanisms that control circadian rhythm earned American scientists Jeffrey C. Hall, Michael Rosbash and Michael W. Young the 2017 Nobel Prize for Physiology. On the basis of studies conducted on fruit flies, they determined how plants, animals and humans adapt their biological rhythm so that it is synchronized with the Earth’s revolutions.

“In each tissue of the body and in small islands of the brain, these molecular clocks work non-stop and regulate sleep. The interaction of the clock neurons creates an endogenous sense of time and regulates how the neuroreceptors turn the clock on and off over time,” he said.

Shafer’s team developed techniques to manipulate these genes, accelerating or delaying the fruit fly clock, and as a result, was able to manipulate the sleep patterns of the flies.

“We now have tools for understanding how these neurons are connected and how everything works. In recent years, we have learned a lot about how this network creates the endogenous system of time and the physiological pathways that link the system to environmental time, particularly to the cycles of light and darkness,” he said.

In addition to the genetic discoveries, studies were conducted at several research centers to determine the characteristics of a population’s sleep pattern. Among the findings, it was discovered that the distribution of chronotype – which causes some people to be more active during the day and others to be more active at night – was replicated in large samples in different cultures.

“On average, the workday begins at 07:55 in the United States. The average start time at schools is 07:59. However, on days off, people on average go to bed at 0:30 and get up at 08:30. People with the chronotype for sleeping later suffer a type of jet lag and its consequences on behavior,” he said.

Shafer explains that chronotype is hereditary, but is also influenced by the environment. It has been shown that because of new habits of artificial light use, there may be an increase in the number of nocturnal people among the population.

“A study conducted by researchers at the University of São Paulo showed there is a major overlap of chronotypes between the São Paulo capital and London. This shows how internal clocks are challenged by modern environments that feature high levels of artificial light and little darkness. It is a problem that is only getting worse, and over time, we will have an increasing number of late chronotypes,” he said. The study was funded by FAPESP.

Given this scenario, Shafer estimates the need for more studies and international collaboration, such as the aforementioned study conducted at USP together with researchers from the University of Surrey, in the United Kingdom.

“This has an impact on quality of life for people. Normally, we would just consider them sleepy and lazy, but it is really as if they are changing times zones all week,” he said.