Discussion

Suicidal ideation significantly increased between time point 2 (May 2020) and time point 3 (August 2020) in the total analytic sample of Japanese employees (N = 875). Factors significantly associated with suicidal ideation were younger age (aged <39 years), suicidal ideation at time point 2 and pre-existing mental health conditions. Loneliness at time point 2 also showed significant association, without adjusting for pre-existing mental health conditions.

Echoing the study findings by O'Connor et al,^{Reference O'Connor, Wetherall, Cleare, McClelland, Melson and Niedzwiedz2} the younger population in both Japan and the UK may be at greater risk of suicidal ideation during the pandemic. In fact, since July 2020, the number of suicides in Japan each month has increased among young people and women compared with that of the same month in 2019.⁶ In more detail, monthly suicide rates in Japan declined by 14% during the first 5 months of the pandemic (February to June 2020), but monthly suicide rates increased by 16% during the second wave (July to October 2020), with a larger increase among women (37%) and children and adolescents (49%).^{Reference Tanaka and Okamoto7} In contrast, there was no significant association with suicidal ideation in gender among full-time employees in this study, whereas suicidal ideation longitudinally increased among women. The literature^{Reference Matilla-Santander, Ahonen, Albin, Albin, Baron and Bolíbar8,Reference Ruffolo, Price, Schoultz, Leung, Bonsaksen and Thygesen9} reported that women who were employed part-time or unemployed may be more affected by COVID-19, but they were not part of our sample. Future monitoring may be worthwhile for the female population, who are more likely to be affected by COVID-19.

Pre-existing mental health conditions and pre-existing suicidal ideation at time point 2 increased the risk of suicidal ideation at time point 3. Pre-existing psychiatric disorders are suggested as one of the risk factors for suicide during the COVID-19 pandemic.^{Reference Raj, Ghosh, Singh, Verma and Arya10} A Chinese cross-sectional study reported that psychiatric patients showed higher suicidal ideation and poorer mental health than healthy controls during early lockdown in the COVID-19 pandemic.^{Reference Hao, Tan and Jiang11} Employees with pre-existing mental health conditions may be at risk.

Loneliness may be one of the key factors in identifying the risk of, and preventing, suicide.^{Reference Stickley and Koyanagi12} As almost all groups showed an increase in loneliness between time points 2 and 3 (Table 2), less social interaction (i.e. social disconnectedness) may universally be taken into consideration in the prolonged pandemic.^{Reference Raj, Ghosh, Singh, Verma and Arya10}

This study had several limitations. We did not measure these variables at time point 1 (baseline), so we could not compare these with early stages of the COVID-19 pandemic. This study has limited generalisability because it was a survey of full-time employees, leading to an underestimation of the risk of suicidal ideation and loneliness by excluding people who were unemployed or who had a precarious job. The generalisability may also be limited by the online recruitment procedure and sampling bias resulting from differences in drop-out rates related to gender, age, occupation and pre-existing mental health conditions. The suicidal ideation of this study was more passive than in previous study the previous study by O'Connor et al,^{Reference O'Connor, Wetherall, Cleare, McClelland, Melson and Niedzwiedz2} which collected data on the frequency of active suicidal ideation, attempts and self-harm attempts (‘How many times in the past week have you thought of taking your life?’). Such a difference may cause overestimation of the frequency of suicidal ideation in this study.

Future studies are needed for practical public health measures to reduce the risk of suicide in the COVID-19 pandemic, investigating both individual risk (e.g. illness) and social risk (e.g. finance, isolation).^{Reference Gunnell, Appleby, Arensman, Hawton, John and Kapur13}

In summary, the results suggest that suicidal ideation of employees has increased from May to August 2020 during the ongoing COVID-19 outbreaks, parallel to the observed increased suicide cases in Japan. Being young, experiencing loneliness, having a pre-existing mental health condition and prior suicidal ideation were suggested to be a risk factor of suicidal ideation. National and community support is needed to target people who are likely to be left behind.^{Reference United Nations14,Reference Sher15}