Publication (in English only)

In press 

  1. Takano, Y., Okajima, I., Ando, T., Iwano, S., & Inoue, Y. (in press). Presenteeism and sleep duration on workdays and days off. Occupational Medicine.
  2. Aoki, Y., Takesu, Y., Matsumoto, Y., Sakurai, H., Tsuboi, T., Okajima, I., Tachimori, H., Komada, Y., Watanabe, K., & Zimmerman, M. (in press). A psychometric analysis of the Japanese version of the Clinically Useful Depression Outcome Scale supplemented with questions for the DSM-5 anxious distress specifier (CUDOS-A). Neuropsychopharmacology Reports.
Published
  1. Matsumoto, Y., Sakurai, H., Aoki, Y., Takesu, Y., Okajima, I., Tachimori, H., Murao, M., Maruki, T., Tsuboi, T., & Watanabe, K. (2024). Assessing the Quick Inventory of Depressive Symptomatology self-report scores to predict continuous employment in mood disorder patients. Frontiers in Psychiatry, 15, 1321611.
  2. Osao, M., Okajima, I., & Inoue, Y. (2024). Cross-sectional analyses of factors associated with the presence and aggravation of chronic insomnia by symptom subtypes. Psychiatry and Clinical Neurosciences Reports, 3(1), e184.
  3. Takano, Y., Ubara, A., Machida, N., Ibata, R., & Okajima, I. (2024). Psychometric properties of the Japanese version of the Insomnia Catastrophizing Scale and relationship of insomnia severity with catastrophic thoughts, safety behaviors and dysfunctional beliefs. Sleep Medicine, 114, 64-72.
  4. Takano, Y., Ibata, R., Machida, N., Ubara, A., & Okajima, I. (2023). Effect of cognitive behavioral therapy for insomnia in workers: A systematic review and meta-analysis of randomized controlled trials. Sleep Medicine Reviews, 71, 101839.
  5. Ibata, R., Takano, Y., Machida, N., Ubara, A., Motoya, R., & Okajima, I. (2023). Development and validation of the Japanese version of the Restorative Sleep Questionnaire in community samples. Sleep Medicine, 108, 45-52.
  6. Futenma, K., Takesu, Y., Komada, Y., Shimura, A., Okajima, I., Matsui, K., Tanioka, K., & Inoue, Y. (2023). Delay sleep-wake phase disorder and its related sleep behaviors in the young generaration. Frontiers in Psychiatry, 14, 1174719
  7. Takesu, Y., Sakurai, H., Aoki, Y., Takeshima, M., Ie, K., Matsui, K., Utsumi, T., Shimura, A., Okajima, I., Kotorii, N., Yamashita, H., Suzuki, M., Kuriyama, K, Shimizu, E., Mishima, K., Watanabe, K., & Inada, K. (2023). Treatment strategy for insomnia disorder: Japanese Expert Consensus. Frontiers in Psychiatry, 14, 1168100.
  8. Okajima, J., & Okajima, I. (2023). Psychometric properties of the Japanese version of the parental acceptance and action questionnaire in parents with infants and toddlers. International Journal of Environmental Research and Public Health, 20, 5674.
  9. Yang, C-M., Lu, Y-Y., Lee, H-C., Li, S-X., Suh, S., Okajima, I., & Huang, Y-C. (2023). Can Adding personalized rule-based feedback improve the therapeutic effect of self-help digital cognitive behavioral therapy for insomnia in young adults? Sleep Medicine, 107, 36-45.
  10. Takano, Y., Iwano, S., Ando, T., & Okajima, I. (2023). Sleep debt madiates the relationship between work-related social factors, presenteeism, and well-being in Japanese workers. International Journal of Environmental Research and Public Health, 20, 5310.
  11. Okajima, I., Kadotani, H., & the NinJa Sleep study group. (2023). Association of sleep reactivity and anxiety sensitivity with insomnia-related depression and anxiety among city government employees in Japan. Clock & Sleep, 5, 167-176.
  12. Suh, S., Nam, H., Chang, J., Trockel, M. T., Okajima, I., Yang, C-M., Chan, N-Y., & Li, S. X.  (2023). Predictors of dropout in university students participating in an 8-week e-mail based cognitive-behavioral therapy for insomnia intervention. Sleep and Breathing, 27, 345-353.
  13. Okajima I. (2022). Is COVID-somnia fact or fiction? Sleep Medicine Research, 13(3), 121-125.
  14. Kadotani, H., Okajima, I., Yang, K., & Lim, M. H. (2022). Editorial: Impact of social isolation and loneliness on mental health and wellbeing. Frontiers in Publich Mental Health. doi: 10.3389/fpubh.2022.1106216.
  15. Ayabe, N., Nakajima, S., Okajima, I., Inada, K., Yamadera, W., Yamashita, H., Tachimori, H., Kamei, Y., Takeshima, M., Inoue, Y., & Mishima, K. (2022). Development and validation of the Japanese version of Hyperarousal Scale. BMC Psychiatry, 22, 617.
  16. Okajima, I., Honda, Y., Semba, O., Kiyota, Y., & Tani, Y.  (2022). Effects of COVID-19-related anxiety and sleep problems on loneliness and feelings of school refusal in adolescents. Frontiers in Psychiatry, 13, 918417.
  17. Tomishima, S., Komada, Y., Tanioka, K., Okajima, I., & Inoue, Y. (2022). Prevalence and factors associated with the risk of delayed sleep-wake phase disorder in Japanese Youth. Frontiers in Psychiatry, 13, 878042.
  18. Chan, N. Y., Lam, S. P., Zhang, J., Chan, J. W. Y., Mandy, Y. M. W., Suh, S., Yang, C-M, Okajima, I., Li, A. M., Wing, Y. K., and Li, S. X. (2022). Efficacy of email-delivered vs. face-to-face group cognitive behavioral therapy for insomnia in youths: A randomized controlled trial. Journal of Adolescent Health, 70(5), 763-773.
  19. Ishii, M., Ito, W., Karube, Y., Ogawa, Y., Tagawa, A., Maeda, S., Sato, H., Takahashi, T., Inomata, N., Narisawa, H., Takaesu, Y., Watanabe, K., & Okajima, I. (2022). Effects of transdiagnostic group treatment for sleep disturbances in adult attention-deficit/hyperactivity disorders and autistic spectrum disorder: A pilot study. Sleep Biological and Rhythms, 20, 173-180.
  20. Ubara, A., Tanizawa, N., Harata, M., Suh, S., Yang, C-M., Li, S. X., & Okajima, I. (2022). How does e-mail-delivered cognitive behavioral therapy work for young adults (18—28 years) with insomnia? Mediators of changes in insomnia, depression, anxiety, and stress. International Journal of Environmental Research and Public Health, 19, 4423.
  21. Aoki, Y., Takaesu, Y., Suzuki, M., Okajima, I., Takeshima, M., Shimura, A., Utsumi, T., Kotorii, N., Yamashita, H., Kuriyama, K., Watanabe, N., & Mishima, K. (2022). Development and acceptability of a decision aid for chronic insomnia considering discontinuation of benzodiazepine hypnotics. Neuropsychopharmacology Reports, 42, 10-20.
  22. Ito, Y., Takeshima, M., Kaneita, Y., Uchimura N., Inoue, Y., Honda, M., Yamadera, W., Watanabe, N., Kitamura, S., Okajima, I., Ayabe, N., Minamizono, S., Nomura, K., & Mishima, K. (2022). Associations between the 2011 great east Japan earthquake and tsunami and the sleep and mental health of Japanese people: A 3-wave repeated survey. Nature and Science of Sleep, 14, 61-73.
  23. Okajima, I., Tanizawa, N., Harata, M., Suh, S., Yang, C-M., Li, S. X., & Trockel, M. T. (2022). Can an e-mail-delivered CBT for insomnia validated in the West be effective in the East? A randomized controlled trial. International Journal of Environmental Research and Public Health, 19(1), 186.
  24. Matsui, K., Komada, Y., Okajima, I., Takaesu, Y., Kuriyama, K., & Inoue, Y. (2021). A cross-sectional study of evening hyperphagia and nocturnal ingestion: Core constituents of night eating syndrome with different background factors. Nutrients, 13 (11), 4179.
  25. Okajima, I., Chung, S., & Suh, S. (2021). Validation of the Japanese-version of Stress and Anxiety to Viral Epidemics-9 (SAVE-9) and relationship among stress, insomnia, anxiety, and depression in healthcare workers exposed to coronavirus disease 2019. Sleep Medicine, 84, 397-402.
  26. Narisawa H., Inoue, Y., Kobayashi, M., Okajima, I., Kikuchi, T., Kagimura, T., Matsui, K., Inada, K., & Mishima, K. (2021). Development and validation of the Benzodiazepine Hypnotics Withdrawal Symptom Scale (BHWSS) based on item response theory. Psychiatry Research, 300, 113900.
  27. Kanda, Y., Takaesu, Y., Kobayashi, M., Komada, Y., Futenma, K.,  Okajima, I., Watanabe, K., & Inoue, Y. (2021). Reliability and validity of the Japanese version of the Biological Rhythms Interview of Assessment in Neuropsychiatry—self report for delayed sleep-wake phase disorder. Sleep Medicine, 81, 288-293.
  28. Okajima, I., Komada, Y., Ito, Y., & Inoue, Y. (2021). Sleep debt and social jetlag associated with sleepiness, mood, and work performance among workers in Japan. International Journal of Environmental Research and Public Health, 18(6), 2908.
  29. Ito, K., Kadotani, H., Okajima, I., Ubara, A., Ichikawa, M., Omichi, C., Miyamoto, T., Matsuda, A., Sumi, Y., & Kitagawa, H. (2021). Large questionnaire survey on sleep duration and insomnia using the TV hybridcast system by Japan Broadcasting Corporation (NHK).  International Journal of Environmental Research and Public Health, 18(5), 2691.
  30. Hara, S., Nonaka, S., Ishii, M., Ogawa, Y., Yang, C-M., & Okajima, I. (2021). Validation of the Japanese version of the Sleep Hygiene Practice Scale. Sleep Medicine, 80, 204-209.
  31. Komada, Y.,Okajima, I., & Kuwata, T. (2020). The effects of milk and dairy products on sleep: A systematic review.  International Journal of Environmental Research and Public Health, 17(24), 9440.
  32. Okajima, I., Miyamoto, T., Ubara, A., Omichi, C., Matsuda, A., Sumi, Y., Matsuo, M., Ito, K., & Kadotani, H. (2020). Evaluation of severity levels of the Athens Insomnia Scale based on the criterion of Insomnia Severity Index. International Journal of Environmental Research and Public Health, 17(23), 8789.
  33. Matsui, K., Kuriyama, K., Yoshiike, T., Nagao, K., Ayabe, N., Komada, Y., Okajima, I., Ito, Y., Ishigooka, J., Nichimura, K., & Inoue, Y. (2020). The effect of short or long sleep duration on quality of life and depression: An internet-based survey in Japan. Sleep Medicine, 76, 80-85.
  34. Okajima, I., Ishii, M., Ochi, M., & Nicassio, P. M.（2020). Development and validity of the Japanese version of the pre-sleep arousal scale. Tohoku Journal of Experimental Medicine, 252(2), 169-176.
  35. Takeshima, M., Utsumi, T., Aoki, Y., Wang, Z., Suzuki, M., Okajima, I., Watanabe, N., Watanabe, K., & Takaesu, Y. (2020). Response to 'Efficacy and safety of bright light therapy for bipolar disorder.' Psychiatry and Clinical Neurosciences, 74(7), 410-411.
  36. Okajima, I., Akitomi, J., Kajimaya, I., Ishii, M., Murakami, H., & Yamaguchi, M. (2020). Effects of a tailored brief behavioral therapy application on insomnia severity and social disabilities among workers with insomnia in Japan: A randomized clinical trial. JAMA Network Open, 3 (4), e202775.
  37. Takeshima, M., Utsumi, T., Aoki, Y., Wang, Z., Suzuki, M., Okajima, I., Watanabe, N., Watanabe, K., & Takaesu, Y. (2020). Efficacy and safety of bright light therapy for manic and depressive symptoms in patients with bipolar disorder: A Systematic Review and Meta-analysis. Psychiatry and Clinical Neurosciences, 74, 247-256.
  38. Takaesu, Y., Utsumi, T., Okajima, I., Shimura, A., Kotorii, N., Kuriyama, K., Yamashita, H., Suzuki, M., Watanabe, N., & Mishima, K. (2019). Psychosocial Intervention for Discontinuing Benzodiazepine Hypnotics in Patients with Chronic Insomnia: A Systematic Review and Meta-analysis. Sleep Medicine Reviews, 48, 101214.
  39. Komada, Y., Okajima, I., Kitamura, S., & Inoue, Y. (2019). A survey on social jetlag in Japan: A nationwide, cross-sectional internet survey. Sleep and Biological Rhythms, 17(4), 417-422.
  40. Ayabe, N., Okajima, I., Nakajima, S., Inoue, Y., Watanabe, N., Yamadera, W., Uchiyama, N., Tachimori, H., Kamei, Y., & Mishima, K. (2018). Effectiveness of cognitive behavioral therapy for pharmacotherapy-resistant chronic insomnia: A multi-center randomized controlled trial in Japan. Sleep Medicine, 50, 105-112.
  41. Kobayashi, M., Okajima, I., Narisawa, H., Kikuchi, T., Matsui, K., Inada, K., Ishigoka, J., & Inoue, Y. (2018). Development of a new benzodiazepine hypnotics withdrawal symptom scale. Sleep and Biological Rhythms, 16(3), 263-271.
  42. Okajima, I., & Inoue, Y. (2018). Efficacy of cognitive behavioral therapy for comorbid insomnia: A meta-analysis. Sleep and Biological Rhythms, 16(1), 21-35.
  43. Okajima, I., & Chen, J. (2017). The effect of insomnia on changes in anxiety, depression, and social function after a transdiagnostic treatment targeting excessive worry. Sleep and Biological Rhythms, 15(3), 243-249.
  44. Nakajima, S., Komada, Y., Sasai, T., Okajima, I., Harada, Y., Watanabe, K., Inoue, Y. (2017). Higher sleep reactivity and insomnia mutually aggravate depressive symptoms: A cross-sectional epidemiological study in Japan. Sleep Medicine, 33, 130-133.
  45. Okajima, I., Nakajima, S., Ochi, M., & Inoue, Y. (2017). Association among changes in sleep-related beliefs, sleep reactivity, and improvement of insomnia following cognitive behavioral therapy. Sleep Medicine, 29, 96-97.
  46. Ito, W., Komada, Y., Okajima, I., & Inoue, Y. (2017). Excessive daytime sleepiness in adults with possible attention deficit/hyperactivity disorder (ADHD): A web-based cross-sectional study. Sleep Medicine, 32, 4-9.
  47. Ito, E., Tsuiki, S., Maeda, K., Okajima, I., & Inoue, Y. (2016). Oropharyngeal crowding closely relates to aggravation of obstructive sleep apnea. Chest, 150(2), 346-352. 
  48. Ishikawa, S., Motoya, R., Sasagawa, S., Takahashi, T., Okajima, I., Takeishi, Y., & Essau, C.A. (2015). Mental Health problems among undergraduates in Fukushima, Tokyo, and Kyoto after the March 11 Tohoku Earthquake. Tohoku Journal of Experimental Medicine, 236(2), 115-122.
  49. Okajima, I., Nakajima, S., Ochi, M., & Inoue, Y. (2014). Reducing dysfunctional beliefs about sleep does not significantly improve insomnia in cognitive behavioral therapy. PLOS ONE, 9(7), e102565.
  50. Nakajima, S., Inoue, Y., Sasai, T., Okajima, I., Komada, Y., Nomura, T., & Takahashi, K. (2014). Impact of frequency of nightmares comorbid with insomnia on depression in Japanese rural community residents: A cross-sectional study. Sleep Medicine, 15(3), 371-374.
  51. Nakajima, S., Okajima, I., Sasai, T., Kobayashi, M., Furudate, N., Drake, C.L., Roth, T. R., & Inoue, Y. (2014). Validation of the Japanese version of the Ford Insomnia Response to Stress Test (FIRST-J) and the association of sleep reactivity with trait anxiety and insomnia. Sleep Medicine, 15(2), 196-202.
  52. Essau, C.A., Ishikawa, S., Sasagawa, S., Otsui, K., Sato, H., Okajima, I., Georgiou, G. A., O'Callaghan, J., & Bray D. (2013). Psychopathological symptoms in two generations of the same family: A cross-cultural comparison. Social Psychiatry and Psychiatric Epidemiology, 48(12), 2017-2026.
  53. Okajima, I., Nakamura, M., Nishida, S., Usui, A., Kanno, M., Nakajima, S., & Inoue, Y. (2013). Cognitive behavioural therapy with behavioural analysis for pharmacological treatment-resistant chronic insomnia. Psychiatry Research, 210(2), 515-521.
  54. Okajima, I., Nakajima, S., Kobayashi, M., & Inoue, Y. (2013). Development and validation of the Japanese version of the Athens Insomnia Scale (AIS-J). Psychiatry and Clinical Neurosciences, 67(6), 420-425.
  55. Takagaki, K., Okajima, I., Kunisato, Y., Nakajima, S., Kanai, Y., Ishikawa, S., & Sakano, Y. (2013). Preliminary assessment of the behavioral activation model in Japanese undergraduate students. Psychological Reports, 112(1), 47-59.
  56. Essau, C. A., Sasagawa, S., Ishikawa, S., Okajima, I., O'Callaghan, J., & Bray, D. (2012). A Japanese form of social anxiety (taijin Kyofusho): Frequency and correlates in two generations of the same family in Japan. International Journal of Social Psychiatry, 58(6), 635-642. 
  57. Komada, Y., Nomura, T., Kusumi, M., Nakashima, K., Okajima, I., Sasai, T., & Inoue, Y. (2012). A 2-year follow-up study on the symptoms of sleep disturbances/insomnia and their effects on daytime functioning. Sleep Medicine, 13(9), 1115-1121.
  58. Sakuta, K., Komada, Y., Kagimura, T., Okajima, I., Nakamura, M., & Inoue, Y. (2012). Factors associated with severity of daytime sleepiness and indications for initiating treatment in patients with periodic limb movements during sleep. Sleep and Biological Rhythms, 10(3), 187-194.
  59. Okajima, I., Komada, Y., Nomura, T., Nakashima, K., & Inoue, Y. (2012). Insomnia as a risk for depression: A longitudinal epidemiological study on a Japanese rural cohort. Journal of Clinical Psychiatry, 73(3), 377-383.
  60. Essau, C. A., Ishikawa, S., Sasagawa, S., Sato, H., Okajima, I., Otsui, K., Georgiou, G. A., O'Callahan, J., & Michie, F. (2011). Anxiety symptoms among adolescents in Japan and England: Their relationship with self-construals and social support. Depression and Anxiety, 28(6), 509-516. 
  61. Komada, Y., Abe, T., Okajima, I., Asaoka, S., Matsuura, N., Usui, A., Shirakawa, S., & Inoue, Y. (2011). Short sleep duration and irregular bedtime are associated with increased behavioral problems among Japanese preschool-age children. Tohoku Journal of Experimental Medicine, 224 (2), 127-136.
  62. Okajima, I., Komada, Y., & Inoue, Y. (2011). A meta-analysis on the treatment effectiveness of cognitive behavioral therapy for primary insomnia. Sleep and Biological Rhythms, 9 (1), 24-34.
  63. Komada, Y., Nomura, T., Kusumi, M., Nakashima, K., Okajima, I., Sasai, T., & Inoue, Y. (2011). Correlations among insomnia symptoms, sleep medication use and depressive symptoms. Psychiatry and Clinical Neurosciences, 65(1), 20-29.
  64. Okajima, I., Kanai, Y., Chen, J., & Sakano, Y. (2009). Effects of safety behaviour on the maintenance of anxiety and negative belief social anxiety disorder. International Journal of Social Psychiatry, 55(1), 71-81
  65. Ishikawa, S., Okajima, I., Matsuoka, H., & Sakano, Y. (2007). Cognitive behavioural therapy for anxiety disorders in children and adolescents: A meta-analysis. Journal of Child and Adolescent Mental Health, 12, 164-172.