Scientists have found that even mild COVID-19 infections may cause insomnia, especially in people with anxiety or depression.

It is already known that insomnia was common in patients who had to be hospitalised, but a team from Phenikaa University, Vietnam, aimed to explore the link in mild COVID patients.

In the article published in Frontiers in Public Health, the team found that the severity of their initial infection didn't seem to correlate with the severity of the insomnia they experienced. Although asymptomatic COVID patients scored lower on the insomnia index, the difference was not statistically significant.

"If you experience insomnia after COVID-19, don't think that is normal," said lead author Huong T. X. Hoang, from the varsity.

"If insomnia does not bother you much, you can take some simple actions, such as: taking a warm shower before bedtime, shutting your phone down at least one hour before going to bed, doing 30 minutes of exercise per day, and avoiding caffeine after 4 p.m.

"In case insomnia troubles you, you can try some over-the-counter sleep aids. If they don't help, go to see a sleep therapist."

For the study, the team recruited 1,056 people over the age of 18 who had been diagnosed with COVID but not hospitalised in the last six months, and who reported no history of insomnia or psychiatric conditions.

They sent out a survey to these people for completion between June and September 2022. About 76.1 per cent of participants reported experiencing insomnia: and 22.8 per cent of these people reported severe insomnia.

Half the participants said they woke more often in the night, while a third said that they found it harder to fall asleep, slept worse, and slept for less time.

Importantly, people who had a pre-existing chronic condition, and people who scored highly for depressive or anxious symptoms showed statistically significant higher rates of insomnia.

Both groups developed insomnia at a higher rate than their peers. When the scientists looked at those patients who reported insomnia, their depression and anxiety scores were higher than the average scores of the entire sample.

However, these illnesses are not completely independent of each other. Insomnia can worsen mental and physical health, as well as being driven by poorer mental and physical health, the team said.