Dear editor,

Since December 2019, the whole world experiences a novel situation due to the outbreak of SARS-CoV-2, leading to the COVID-19 pandemic. Fear of contamination and radical changes to everyday life are expected to impose stress on individuals, seriously affecting mental health, including sleep hygiene.

Aiming to examine the impact of the COVID-19 pandemic on sleep health in a Greek population, we conducted a web-based study during April 2020, three weeks after a national lockdown had been imposed in Greece (April 10-April 13). Of the 2,427 participants, a total of 2,363 subjects, provided all basic demographic data needed [1,800 females (76.2%); 563 males (23.8%); 55% within the age range 18-30 years; the majority (76.5%) were urban citizens]. The participants completed the following questionnaires: Athens Insomnia Scale (AIS) (^{Soldatos et al., 2003}), Intolerance to Uncertainty Scale (IUS-12) (^{Carleton et al., 2007}), De Jong Gierveld Loneliness Scale (JGLS) (^{Gierveld and Van Tilburg, 2006}), Brief Patient Health Questionnaire 2 (PHQ-2) (^{Kroenke et al., 2003}). Additionally, they responded to questions assessing COVID-19-related negative attitudes (worry, unpredictability, lethality) and others exploring if they, or someone close to them, had contracted the virus.

In this study, 37.6% of the participants scored above the cut-off score for insomnia. This percentage is greater than the worldwide insomnia prevalence, estimated before the pandemic between 3.9% and 22% (^{Kay-Stacey and Attarian, 2016}) indicating an exacerbation of sleep disturbances. With regard to sociodemographic factors, the women's insomnia score (MAIS = 13.31, SD = 4.35) was significantly higher than men's (MAIS = 11.78, SD = 3.75) [t(2358) = −751, p = 0.001]. Urban citizens also scored higher (MAIS = 13.11, SD = 4.26) than rural residents (MAIS = 12.15, SD = 3.93) [F(2,2397) = 6.866, p < 0.001]. A non-significant trend for greater sleep difficulties in younger ages (18–30) was also noted.

Interestingly, those responding “I don't know” when asked if they had contracted the virus, scored significantly higher (MAIS = 13.75, SD = 4.55) [F(2,2374) = 12.23, p < 0.001)] in AIS that those answering “yes ” (MAIS = 11.83, SD = 1.83) or “no” (MAIS = 12.73, SD = 4.16). The same pattern was held when asked if someone close to them had contracted the virus. Those replying “I don't know” showed higher scores (MAIS = 13.92, SD = 4.67) [F(2,2413) = 11.65, p < 0.001] than those responding “yes” (MAIS = 13.16, SD = 4.83) or “no” (MAIS = 12.76, SD = 4.15).

A multiple linear regression was conducted to predict insomnia (AIS) based on the significance of the positive correlation of the independent variables. A significant equation was found [F(4,2030) = 331,928 p < 0.001] with an R ² of 0.395. Participants’ predicted insomnia was equal to 3.232 + 0.398 (JGLS) + 1.338 (PHQ-2) + 0.63 (IUS) + 0.178 (COVID-19 worry).

This study revealed several interesting aspects related with sleep health. Insomnia seems to be affecting more people during the COVID-19 pandemic. Stress levels rise during a virus outbreak due to worry about health, financial consequences, changes in social life and the daily routine. Reduced physical fatigue and exposure to the sun, as well as increased use of electronic devices may also affect sleep homeostasis. Women seem to be more vulnerable, a finding compatible with the evidence suggesting that they are more prone to stress-related disorders such as post-traumatic stress disorder and anxiety disorders (^{Li and Graham, 2017}). Rural residence may act protectively, providing more opportunities for physical activity and exposure to natural environments, as well as less strict application of restrictive measures. As suggested by the regression analysis, intolerance to uncertainty was associated with insomnia. Living in the pandemic, unaware of multiple aspects of this novel situation (e.g. virus transmission rate, morbidity) imposes stress on individuals struggling to deal with uncertainty. Ruminating thoughts provoking cognitive arousal and unpleasant physical reactions also hinder sleep promotion. This is in line with previous findings (^{Lauriola et al., 2019}) and may also explain the high AIS scores in those answering “I don't know” when asked if they, or someone else close to them, had contracted the virus, since this answer suggests uncertainty. In this study, COVID-19 worry was also associated with insomnia. Worry provokes cognitive arousal and may therefore disturb sleep through this mechanism. Loneliness also showed a positive correlation with insomnia. There is evidence of a bidirectional relation between loneliness and insomnia. Loneliness may induce increased feelings of vulnerability, hence arousal, disturbing sleep. Conversely, poor sleep increases frustration related with feelings of isolation and may disturb contact with others e.g. due to abnormal sleep-wake schedule. Dysregulation of the hypothalamic-pituitary-adrenal axis may also be involved (^{Griffin et al., 2019}). Finally, this study demonstrated an association between sleep and depression. This a well-established observation, since insomnia is considered an important precedent to depression, as well as a predictor of a depressive episode's relapse. Monoamines, inflammation, genetic factors and dysregulation of the circadian rhythm may be implicated in the pathophysiology (^{Fang et al., 2019}).

In conclusion, insomnia constitutes a major health issue. Up to date, research of insomnia during a pandemic crisis is limited. To the best of our knowledge, this was the first study to explore sleep difficulties during the COVID-19 pandemic in a Greek population. This study revealed a high frequency of insomnia during the COVID-19 pandemic. Women and people living in urban areas were more susceptible to sleep difficulties. Unawareness of potential contact with COVID-19, intolerance to uncertainty, COVID-19-related worry, loneliness and depressive symptoms were significantly associated with insomnia. These findings may contribute to the management of insomnia during the COVID-19 pandemic. Provision of simple and clear information about the outbreak to combat uncertainty and worry, enhancement of social contact with the aid of technology, as well as the providence for screening and treatment of depression and anxiety may improve sleep difficulties.