Table 1.
Prevalence of DSWPD-related disorders by region/country as reported over the past decade.
| Region/country (author, year) | Prevalence/sex difference | Study design (n/age in years) | Findings |
|---|---|---|---|
| Europe | |||
| Norway (Sivertsen, 2021) | 3.3% (DSWPD)/male, 4.7% > female, 2.7%** | Cross-sectional study (50,054/18–35) | Single status, financial difficulties, parental divorce, obesity, and physical inactivity were associated with DSWPD. |
| Norway (Hysing, 2018) | 3.9% (DSP)/n.s. | Longitudinal study (2,200/16–19) | Sleep duration of < 9 h/night at the age of 11–13 years was associated with DSP at 16–19 years. |
| Sweden (Danielsson, 2016) | 4.0% (DSPD)/n.s. 4.6% (DSP)/male, 7.3% > female, 2.4%* | Cross-sectional study (10,000/16–26) | DSPD was associated with non-attendance of educational activities or work and elevated levels of anxiety. |
| Norway (Sivertsen, 2013) | 3.3% (DSPS)/female, 3.7% > male, 2.7%* | Cross-sectional study (9,338/16–18) | DSPS was associated with non-attendance at school, with half of the adolescents with DSPS also meeting the criteria for insomnia. |
| Norway (Saxvig, 2012) | 8.4% (DSP)/n.s. | Cross-sectional study (1,285/16–19 years) | DSP was associated with lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores. |
| Asia | |||
| Japan (Tomishima, 2022) | 4.3% (at risk of DSWPD)/ female, 4.9% > male, 2.5%** | Cross-sectional study (7,810/15–30) | Long-term LCD viewing at night and relatively loose social constraints were associated with the presence of DSWPD. |
| Oceania | |||
| New Zealand (Paine, 2014) | 1.51% (DSPD)/n.s. | Cross-sectional study (4,386/20–59) | DSPD prevalence was higher in deprived areas and decreased with age. This disorder was associated with the presence of night work. |
| Australia (Lovato, 2013) | 1.1% (DSPD)/n.s. | Cross-sectional study (374/13–18) | Patients with DSPD showed relatively greater alcohol and caffeine consumption, lesser sports participation, and more time spent on extracurricular activities. |
DSP, delayed sleep phase; DSPS, delayed sleep phase syndrome; DSPD, delayed sleep phase disorder; DSWPD, delayed sleep–wake phase disorder; LCD, liquid crystal display; n.s., not significant. *p < 0.05, **p < 0.001.