It only takes one night of sleep loss for the genes that control the biological clocks in your cells to be altered. That’s the conclusion of a new, small study published in the Journal of Clinical Endocrinology and Metabolism.
Swedish researchers at Uppsala University and the Karolinska Institute were already aware that sleep loss negatively affects metabolic responses in both animal models and humans. While shortened sleep has been linked to particular changes in our clock genes, little is known about the effect of staying up all night, like those who do shift work, on the circadian machinery in tissues. This is particularly important as “at least 15% of the workforce – numbering 15 million in the U.S. alone – carry out shift work, with job activities scheduled during the biological night,” the paper notes.
Researchers recruited 15 healthy men of normal weight for the study. They were asked to stay at the lab on two separate occasions for almost two nights each. They slept as usual in one session and were kept awake in the other. Researchers strictly controlled light conditions, food intake and activity levels in the lab to minimize the influence of environmental factors. Volunteers were under constant supervision in the sleep deprivation condition.
Blood samples were extracted from the volunteers after they were given a sugar solution. This allowed researchers to test the participants' insulin sensitivity so they could rule out the presence of diabetes. Researchers also removed small tissue samples from the participants' superficial stomach fat.
“Our current results indicate that changes of our clock genes may be linked to such negative effects caused by sleep loss,” says Jonathan Cedernaes, lead author on the study, in a statement.
What stood out for the researchers was how rapidly the activity of clock genes changed after just one night of sleep loss. They found that within the clock genes, the DNA molecule underwent chemical alterations, or epigenetic changes, which are known to affect the way genes are expressed. In this process – known as methylation – proteins attach methyl groups to the bases of the DNA molecule in particular places. Methyl groups are able to control how the genes are switched on or off by regulating the interactions between the DNA and other proteins.
“It was interesting that the methylation of these genes could be altered so quickly, and that it could occur for these metabolically important clock genes,” Cedernaes added.
Researchers found that sleep loss increased DNA methylation and altered the expression of clock genes in the participants' tissues. For now, researchers are unsure over the longevity of these changes.
“It could be that these changes are reset after one or several nights of good sleep. On the other hand, epigenetic marks are suggested to be able to function a sort of metabolic memory, and have been found to be altered in e.g. shift workers and people suffering from type 2 diabetes,” Cedernaes explained.