Humans May Be Hardwired to Work 8 Hours per Day

A new scientific study of the circadian rhythm, the pace inside the human brain that governs our daily sleep-wake routine, seems to indicate that we are hardwired to follow an eight-hour working schedule. A number of genes in our bodies is controlled by this rhythm, and some of them are only activated once a day, at specific times. Experts at the University of Pennsylvania School of Medicine and the Salk Institute for Biological Studies have recently demonstrated that gene expressions also occur once every eight and 12 hours, which means that the circadian pace may also be divided into smaller cycles that are also encoded in the human genome.

For their new study, the researchers used a novel approach – surveying gene expression inside the liver of an innocent mouse every hour, for 48 consecutive hours. During this time, they also discovered that the number of genes expressed every day was, in fact, ten times higher than previously held.

They used a proprietary time-sampling technique for the task, and the results were amazing even to them. In addition, their groundbreaking study was also the first in the world to prove that the body was not only governed by a 24-hour cycle, but that smaller subdivisions also existed.

The finds may lead to experts developing future treatments for disruptions of circadian rhythms, which trigger conditions such as cardiovascular and metabolic diseases, cancer, and aging-related disorders, ScienceDaily reports. The finds appear in this month's issue of the journal PLoS Genetics.

“The principal frequency, which is not a surprise, is the 24-hour cycle, and it is the most prevalent. What was a surprise to us – although we set up the experiment to see exactly this – are the 12-hour and the 8-hour cycles,” Penn Institute for Translational Medicine and Therapeutics Associate Professor of Pharmacology John Hogenesch, PhD, who has also been the senior author of the study, explained.

“There is an obvious biological basis to a 12-hour rhythm. The 12-hour genes predicted dusk and dawn. These are two really, really stressful transitions that your body goes through and your mind goes through. Anybody who has young children realizes that they are more likely to cry around those times – and you’re more likely to cry with them,” the expert added. According to previous studies, it's the time when these genes are expressed that helps animals in the wild, for instance, get ready for the behavioral changes that they exhibit when night turns to day and vice-versa.

“We have less of a handle on the 8-hour rhythms, but the fact that we can see them reliably means to me there is the possibility that there could be a biological basis to an 8-hour cycle,” Hogenesch also shared. “The largest previously identified sets included 400 to 500 circadian-controlled genes and now we have 3,000 that are oscillating in the liver. We were able to more precisely say that, for example, the pituitary gland has 10-fold fewer oscillating protein transcripts than the liver, and cell-autonomous models have 10-fold less than that,” he concluded.