The risk of long COVID maybe three times higher among people who sleep less than six hours per night and also have pre-existing medical conditions, finds a study.

In contrast, the risk of long COVID-19 in people with pre-existing conditions was only 1.8 times higher among people with an average nightly sleep duration. 

These analyses were adjusted for potential confounders including sex, age, body mass index, and vaccination status.

“Habitual short nighttime sleep duration exacerbated the risk of long COVID in individuals with pre-existing conditions,” said Frances Chung, Professor at the University of Toronto’s Department of Anesthesiology and Pain Medicine. 

“Based on its proven adjuvant role in immunity, habitual sleep duration may alter the risk for developing long COVID,” he added.

Long COVID was defined as having a history of COVID-19 infection with at least one symptom lasting for more than three months according to the definition of World Health Organisation. 

Long COVID symptoms may include tiredness or fatigue, difficulty breathing or shortness of breath, sleep problems, and difficulty thinking or concentrating (sometimes referred to as “brain fog”).

The study, published in the Journal of Clinical Sleep Medicine, analysed data from an online survey of 13,461 adults from 16 countries. Participants were categorised as COVID-19 cases if they indicated that they had tested positive for the infectious virus. Participants reported how many hours per night they slept on average.

Of survey participants, there were 2,508 individuals who reported having a COVID-19 infection, and 20 per cent reported at least one long Covid symptom. 

Of the 1,505 participants with long COVID who also reported their sleep duration and pre-existing condition status, 945 had pre-existing conditions, 560 had none; 121 (8 per cent) were short sleepers, 1,257 (83.5 per cent) had an average sleep duration, 127 (84 per cent) had a long nightly sleep duration of more than 9 hours.

According to Chung, sleep duration is a target for interventions to reduce the risk of long-term COVID-19.

“Restoring nighttime sleep to average duration represents a potentially modifiable behavioural factor to lower the odds of long COVID for at-risk patients,” she said.

The team noted that more research is needed to understand the pathophysiology of long-term COVID-19.