Your biological clock is probably the most reliable machinery in your body: it runs 24-7 to regulate vital functions from sleep to metabolism and remains stubbornly steadfast when you fly across time zones. Scientists still don’t know exactly how this this internal clock works. But now researchers have identified a missing gear that could offer a cure for jet lag.
A recent study published in the Journal of Physiology discovered a new group of cells in the retina that send signals about light changes from the eye to the brain. These cells produce and release a molecule called vasopressin to help regulate the biological clock or the circadian rhythm of rats.

Scientists already knew that vasopressin plays a role in hypothalamus’ suprachiasmatic nucleus (SCN), the center for circadian rhythm in the brain, but this is the first research to show a retinal input of vasopressin. In theory, one could tweak the behavior of these cells within the eye to reduce vasopressin signaling—which could help regulate your internal clock and kick jet lag to the curb.

“In humans, you can't inject anything into the brain. But you could think about [applying] eye drops into the eye and then help to reset your biological clock,” says the leading author Mike Ludwig, a professor of neurophysiology at the University of Edinburgh in Scotland. “But that is very futuristic. We are far from that at the moment,” Ludwig says.
Hugh Piggins, an expert in circadian rhythm at the University of Manchester who was not involved in the study, agrees that “this is very basic research, but it raises some exciting possibilities.”

“We've known for a long time that you can combat things like jet lag by controlling how much light you're exposed to, what times of the day you get up... That's just dealing with light,” Piggins says. “This [study] would say that maybe there's another way.”

Animals have already been cured of jet lag through the inhibition of vasopressin—a 2013 study published in Science tested such a method. “If you interfere with the signaling of vasopressin [in the SCN]… these animals don’t seem to have jet lag,” says Ludwig. When researchers changed light-night cycles in their experiment, the animals reset their biological clocks immediately.

Regarding the current study, Piggins says one can speculate that these retinal vasopressin cells could be involved in jet lag, “but the complication is that some of the brain clock cells themselves also make vasopressin.”
“So it's going to be very complicated to determine what vasopressin made by the clock cells does versus what vasopressin coming from the eye does,” he says.

In addition, one must remember that vasopressin also plays important roles in regulating blood pressure and fluid balance in the body, says Piggins. “It's involved in many other processes other than how light is communicated to the brain,” so a drug that acts on vasopressin signaling might have other effects.

Study author Ludwig is also cautious. “We still need to understand what the mechanism of the signaling in the SCN is,” he says. “[The eye drop] may never work, because still you have to get things into the eye [and] it has to act on the cells. It's a very long way to go.”

Currently, the only thing available to treat jet lag is melatonin, says Michael Iuvone, a professor of ophthalmology at Emory University who was not involved in the study. “It also acts on the SCN and has some effects there. But it's not all that effective. It does work in some people, but not everybody.”

“I think the major significance of the study is that it creates a new avenue of research that may allow us to ultimately regulate circadian biology,” Iuvone says. “And there's potential there for treating sleep disorders and other types of circadian disorders that are related to the circadian clock.”