Ask anyone struggling to get their nightly rest — lack of sleep can be a serious detriment to one’s mental health.

But while the link between lack of shuteye and the sads is already well understood, scientists have heretofore gathered surprisingly little evidence to prove which comes first — the insomniac chicken, or the very depressed egg.

Now, researchers in the United Kingdom have released fresh data that reveals those consistently sleeping five hours or less per night were 2.5 times more likely to wind up grappling with the gloomies, The Guardian reported.

“We have this…scenario between suboptimal sleep duration and depression. They frequently co-occur, but which comes first is largely unresolved,” said the University College of London’s Odessa Hamilton, first author of the study.

Those studied averaged seven hours of sleep per night. Approximately 10% of participants got less than five hours’ sleep per night at the beginning of the study period — that number climbed to more than 15% by the end. The percentage of those struggling with symptoms of depression went from about 9% to 11%.

Earlier research has showed that sleep duration and depression can be inherited, the outlet stated..

Tracking the participants over a lengthy period, the study authors discovered that those genetically inclined toward taking less than 5 hours of sleep per night were more likely to show signs of depression over four to 12 years. Researchers also found, however, that those predisposed to depression weren’t more likely to have issues with their sleep.

Researchers gathered both health and genetic data from 7,146 participantss, recruited by the English Longitudinal Study of Ageing, or ELSA.

But while the findings, which were published in the journal Nature Translational Psychiatry, might be cause for, well, depression, Hamilton encouraged those suffering from one issue or the other not to view their situation as irreversible.

“My advice would be to prioritise sleep and to avoid sleep procrastination,” the PhD candidate said. “There’s this common saying in genetics that genes load the gun and environment pulls the trigger. You might be genetically predisposed to this, but you can take steps to mitigate the risk.”