The study showed a considerable reduction in the prevalence of possible insomnia on removal of the diagnostic criterion 'non-restorative sleep'. Thus, there was a considerable percentage of participants who had earlier received the insomnia diagnosis on the basis of non-restorative sleep who had no difficulty initiating or maintaining sleep. Using the new criteria for insomnia results in a considerable reduction in prevalence, as shown previously in a study of a normal population
One of the arguments for changing the diagnostic criteria is that it is more likely that those with non-restorative sleep suffer from sleep disorders other than insomnia, such as obstructive sleep apnoea. This is the most common sleep disorder after insomnia
(13). One of the main symptoms of sleep apnoea is increased tiredness during the day due to poor sleep quality. People with non-restorative sleep may not have insomnia in the usual sense but have sleep apnoea or other sleep disorders that make them feel inadequately rested after sleep. Removing non-restorative sleep from the diagnostic criteria for insomnia may exclude those who previously received the diagnosis on an incorrect basis, thus refining the insomnia diagnosis. Insomnia and sleep apnoea are treated differently, and more accurate diagnosis will have a bearing on the choice and efficacy of treatment.
Our study showed a high prevalence of possible anxiety and depression among participants with insomnia according to the DSM-5 criteria. In comparison, the HUNT-3 study (Nord-Trøndelag Health Study) has demonstrated a prevalence of possible anxiety of 34.6 % and of possible depression of 29.8 % among participants with insomnia
(7). HUNT-3 used the HADS score to determine the anxiety and depression diagnoses, as we also did in our study. In contrast, insomnia was not diagnosed using a validated questionnaire. A possible explanation of the difference in prevalence may be, therefore, the use of different criteria to determine the diagnosis. Another possible explanation is that the sample in HUNT-3 was random rather than including persons who had reported sleep problems as a point of departure. Finally, the HUNT-3 study was conducted in the period 2006–08, and the prevalence of insomnia has increased in the general population since then (1, 2).
The study showed a significantly higher prevalence of possible anxiety and depression among participants who met the DSM-5 criteria for insomnia than among those who did not meet the new criteria. Earlier studies have shown a clear association between insomnia, anxiety and depression
(4, 7, 8). Our findings indicate that the new diagnostic criteria strengthen this association. The association between sleep apnoea, anxiety and depression (14) has not been shown to be as strong as that between insomnia, anxiety and depression (4, 7, 8). More accurate diagnosis of people with insomnia may therefore explain why the association between insomnia, anxiety and depression is strengthened when using the new diagnostic criteria. Therefore, we recommend further research on the prevalence of other sleep disorders among those with non-restorative sleep.
The introduction of new diagnostic criteria will probably mean that a larger percentage of patients with insomnia will have comorbid mental disorders. Thus, it will be important to continue to focus on diagnosing and treating comorbid mental disorders in patients with insomnia.
Strengths and limitations
Strengths and limitations
A major strength of the study was the large number of participants. This made it easier to establish statistical differences. However, there is a danger that the differences are not necessarily clinically relevant. A limitation of the study was that many participants did not answer the questions about insomnia, anxiety and depression. It is important to emphasise that the dataset was selected. Many participants were recruited as a result of publicity in the Dagbladet newspaper or on TV2.no. In addition, the participants were obliged to report a sleep problem to take part in the survey. Therefore, the survey gives no indication of the actual prevalence of insomnia, anxiety and depression in the population. Another weakness of this type of survey is that the diagnosis is not made through direct contact with patients. Consequently, we lose the opportunity to acquire vital clinical information that can affect the setting of the diagnosis. Moreover, there will be greater uncertainty as to whether the participant has understood the question correctly. In order to arrive at a precise diagnosis, a clinical interview is necessary.
A strength of the study was that a validated questionnaire for insomnia, anxiety and depression was used. The questionnaires (Bergen Insomnia Scale and HADS) have been widely used in the field of sleep research and in major studies of anxiety and depression. A weakness of the Bergen Insomnia Scale is that it is validated on the basis of DSM-IV criteria rather than DSM-5 criteria. A weakness of the HADS questionnaire is that the questions are limited to covering the non-vegetative symptoms of anxiety and depression, which means that symptoms such as tiredness, fatigue, sleep problems and headache are not included in the questionnaire