The vast majority of people with insomnia in the UK cannot access the first-line treatment (CBT). The HABIT trial sought to test whether brief nurse-delivered behavioural treatment for insomnia in primary care is clinically and cost-effective. The trial shows that nurses without prior clinical experience of sleep disorders or sleep intervention can be successfully trained to deliver SRT in a brief and manualised manner, and with high levels of fidelity. Results indicate superiority of nurse-delivered SRT over SH in reducing insomnia symptoms at all time points. Cost–utility analysis suggests that the intervention is likely to be cost-effective at established willingness-to-pay thresholds. Below we consider trial results in relation to the broader literature, and reflect on the generalisability of findings and potential implications for the management of insomnia in the UK (and beyond).
Clinical effectiveness
To our knowledge, HABIT is the largest randomised trial to date of a psychological treatment for insomnia delivered in a clinical setting. It is also one of the few controlled studies to follow up patients for 12 months.71 Standardised effect sizes for the ISI were in the medium-to-large range at all time points, and multiple sensitivity analyses of the primary outcome suggest robustness to a range of assumptions regarding missingness. Descriptive data on treatment response (defined as ≥ 8 points on the ISI) parallel these changes (42% for SRT vs. 17% for SH at 6 months). Treatment effects exceed clinically significant thresholds defined by the American Academy of Sleep Medicine (AASM) Task Force on Behavioural and Psychological Treatments for Insomnia,38 as well as estimates from a recent meta-analysis of CBT-I trials performed within primary care (g = 0.40).21 Moreover, pre-specified moderation analyses of the primary outcome revealed no significant effects for age, depression severity, chronotype, actigraphy-defined sleep duration, sleep-medication use, or level of deprivation, which is broadly consistent with meta-analyses looking at variability in effect sizes across trials.72
While sleep diary data were available for only a minority of HABIT participants at follow-up, small-to-medium effects were found for sleep continuity variables (WASO, SE, SQ and TST) at both 6 and 12 months relative to control. Actigraphy-defined WASO and SE were also improved in the SRT group at 6 months, but not 12 months, and TST was reduced (by 13–15 minutes) at both time points. Results are broadly consistent with previous work showing that diary-recorded sleep is more sensitive to change following CBT relative to actigraphy.73
In addition to improvements in insomnia we also observed treatment effects at all time points on several important secondary outcomes, including mental health-related and sleep-related quality of life, depressive symptoms, and work productivity and activity impairment. Effect sizes were in the small-to-medium range, consistent with meta-analysis of CBT for insomnia.74 Treatment effects tended to be greater for patient-generated quality of life (GSII) relative to standardised measures (SF-36), presumably because the GSII is an idiographic measure, which increases signal-to-noise by measuring life domains important to each individual patient.3,39 These results are important because the daytime consequences of insomnia are distressing for patients and the most common reasons for seeking treatment in primary care.3,75 Effects on mental health outcomes are particularly noteworthy given the strong association between insomnia and psychiatric disorder.76 For example, approximately 40% of the sample had a mental health condition at baseline and 49% met criteria for depression on the PHQ-9. Results suggest that targeting insomnia leads to a small and sustained reduction in depressive symptoms, which was also reflected in a reduction in depression ‘caseness’ (defined as PHQ-9 ≥ 10) between groups at 6 months (SRT = 29% vs. SH = 39%). While we did not specifically recruit a sample with depression, nor target depression during treatment, it is interesting that effect sizes appear similar in magnitude to those observed in trials of CBT for depression in primary care (assessing various delivery formats).77 Given that insomnia is almost characteristic of depression, the specific management of insomnia through SRT may lead to improved mental health outcomes.
No group differences were found for number of nights of use, or proportion of participants using prescribed hypnotic or sedative medication at 6 or 12 months. Missing diary data due to the pandemic may have limited power to detect group effects for medication use; however, exploratory analysis of prescription data collected from practice records at 12-month follow-up also revealed similar proportions of participants in each arm being prescribed sleep-promoting hypnotic medication (SRT = 25.5% vs. SH = 25.1%). Conflicting findings have been observed in the CBT treatment literature,78 particularly for studies where hypnotic use was not an inclusion criterion, or where the intervention did not specifically have a focus on withdrawal or tapering of medication (both apply to the HABIT trial). It would be interesting to specifically test the effects of nurse-delivered SRT on long-term users of hypnotics, or alternatively investigate those first presenting to primary care with insomnia to ascertain whether offering SRT lessens prescriptions and use of sedative hypnotics.
HABIT is the first trial in the CBT field to rigorously measure SAEs and pre-defined AEs.79 This was considered important because previous work has documented increased sleepiness, reduced psychomotor vigilance, and potential driving concerns during implementation of SRT,24,29,70 owing to the acute effects of restricted sleep opportunity. While participants reported challenges with sleepiness and fatigue during qualitative interviews (consistent with previous work29), we found no evidence that falls, accidents (including road traffic accidents and near misses) or sleepiness while driving were increased at any post-randomisation assessment. This was also the case for SAEs, which were infrequent, similar between arms, and not judged to be related to the intervention. Our nurse-delivered protocol emphasised to patients the importance of avoiding driving if sleepy. Moreover, nurses were able to modify the sleep window if participants reported concerns with excessive daytime sleepiness or experienced difficulties with adherence. Such flexibility in the delivery of SRT is important, particularly in routine clinical practice where patients have a range of comorbidities. Nevertheless, findings from the process evaluation suggested that participants still found the treatment challenging, prompting some participants to discontinue with the intervention. Descriptive data on reasons for withdrawal from intervention showed that 35 participants (11% of those randomised to SRT) discontinued due to lack of benefit or finding the intervention too challenging to implement.
It is known that SRT is the most challenging component of CBT for insomnia80–83 – yet potentially the most active. Restricted sleep opportunity is central to driving clinical outcomes,25,26 and HABIT data show stronger treatment effects for participants who attend more treatment sessions and more closely adhere to prescribed bed and rise times. It would be prudent, therefore, for future studies to test strategies that may improve treatment engagement and adherence. For example, one strategy that could be tested is the combination of light therapy and SRT. Bright light is known to have alerting properties84,85 and has been shown to reduce the impact of experimental sleep restriction on sleepiness and vigilance when administered during the day.86–88 Moreover, light acts as the main zeitgeber for the synchronisation of the circadian rhythm. Regular and enhanced light exposure alongside a prescribed sleep opportunity may strengthen the circadian rhythm and help align homeostatic and circadian drives for sleep, a proposed mechanism of SRT.23 Other potential refinements could include involving family members in treatment to support behaviour change and reduce obstacles to implementation,89 or prescription of a more gradual reduction of time in bed (sleep compression) for those who find SRT challenging.
While 92% of participants attended at least one out of four treatment sessions, 65% completed all four. Our numbers are consistent with or higher than other primary care trials of in-person CBT for insomnia20,31,90 and exceed rates of engagement found for other low-intensity interventions, such as digital CBT.39,52,91–93 Qualitative interviews with nurses and patients also generated areas of potential refinement that could support treatment engagement. For example, digital technology (app and/or wearable device) could be blended with nurse-delivered SRT to automate recording and calculation of SE to reduce participant burden. Additional follow-up sessions with the nurse were suggested as a way to help maintain sleep behaviour change beyond the acute intervention phase. There is suggestive evidence from meta-analysis that > 4 sessions may yield enhanced treatment effect sizes72 but this must be balanced against cost and scalability in primary care, particularly when considered within a stepped care framework. Such refinements could be explored in future research, but it is worth noting that the proportion of participants achieving a treatment response in the present study (42%) is similar to a high-quality trial that assessed eight weekly sessions (45–60 minutes in duration) of behavioural therapy delivered by licensed or trainee clinical psychologists (44%).94
The HABIT trial was not designed to evaluate treatment mechanisms, but we performed mediation analyses to enhance understanding of how SRT may exert its effects. Drawing on a theoretical model of SRT mechanism of action,23 we examined the mediating role of pre-sleep arousal and sleep effort on insomnia severity. SRT led to reductions in pre-sleep arousal and sleep effort at 3 months, which significantly (though modestly) mediated the treatment effect on the ISI at 6 months. Proportion mediated was larger for cognitive measures [sleep effort (36%), cognitive arousal (35%)] vs. self-reported somatic arousal (15%). Excessive pre-sleep arousal and sleep effort are reliable features of insomnia and may be involved in the maintenance of poor sleep via effects on autonomic and cortical arousal prior to and during the sleep period, which ultimately degrades sleep quality. Integrating previous experimental work25,29 with HABIT findings we hypothesise that enhancing sleep pressure and regularising time in bed reduce arousal and obviate sleep effort, leading to improved sleep consolidation. Improved sleep consolidation and quality then positively influence cognitive processes that operate during daytime periods (e.g. sleep-related worry and monitoring), which further lessens pre-sleep arousal and sleep effort in the evening. While this sequence and feedback loop needs to be appraised in dedicated studies – alongside other putative causal mechanisms – HABIT suggests that addressing arousal (especially cognitive arousal) and sleep effort may be important in lessening insomnia severity.
Cost-effectiveness
The HABIT trial was designed to test a scalable and potentially cost-effective treatment for insomnia in primary care. Health economic analysis showed that the cost of brief SRT was modest at £52.60 per trial participant and mean NHS and PSS costs (excluding intervention-related costs) were similar between arms over the 12-month period. In the primary analysis, mean NHS and PSS costs (including intervention-related costs) were just £43.59 (95% CI −18.41 to 105.59) higher in the SRT arm compared to control. Adjusting the SRT training cost to reflect what may happen in clinical practice (trained nurses seeing a much larger number of patients) led to a small difference of just £14.41 (−47.59 to 76.41). In terms of utility, the EQ-5D-3L showed a small difference of 0.021 in QALYs in favour of SRT. Nevertheless, small differences in both QALYs and costs produced an incremental cost-effective ratio of just £2075.71 per QALY with a high probability (95%) that the intervention is cost-effective at a cost-effectiveness threshold of £20,000 per QALY (NMB = £377.84). This was supported by a range of sensitivity analyses. Indeed, a probability of 94.4% of cost-effectiveness was estimated at a cost-effectiveness threshold of just £15,000. Poor sensitivity of the EQ-5D-3L to insomnia interventions has been reported in several trials,95–97 contrasting with effects for insomnia-specific outcomes like the ISI. In exploratory analyses we also performed cost–utility analyses using the SF-6D and EQ-5D-3L + Sleep. Both measures showed a small advantage in QALYs relative to control, and with slightly higher levels of decision certainty than the EQ-5D-3L (96.3% and 100% probability of being cost-effective at the £20,000 cost-effectiveness threshold).
HABIT is the largest trial to date to assess cost-effectiveness of a psychological treatment for insomnia and the only trial to assess costs and effectiveness over a 12-month horizon. Results provide robust support for the cost-effectiveness of nurse-delivered SRT. Our trial compares favourably to smaller studies adopting a similar approach but over a shorter time-frame, where probability of cost-effectiveness was 67% (at a £20,000 cost-effectiveness threshold) for guided digital CBT-I96 and just 34% (at a £30,000 cost-effectiveness threshold) for community-based CBT workshop delivery.95
HABIT intervention costs are also lower than other low-intensity interventions that have been trialled in primary care [e.g. £148 for community-delivered workshops,95 £191 for counsellor-delivered CBT31 and £85 pounds (99 euros) for nurse-guided digital CBT96]. While SRT does not appear to be cost-saving for the NHS over a 12-month horizon (that is, resource use was broadly similar between arms), we did find that SRT dominated SH from a societal perspective with societal costs being reduced, on average, by £1086.13 (−1485.59 to −686.67) in the SRT arm compared to control. These differences principally reflected reduced productivity loss in the SRT arm.98,99
We focused on self-reported health and social care resource use for insomnia and, as a consequence, there was a high degree of missing data compared to data extracted from practice records. Nevertheless, sensitivity analyses across both imputed and complete data sets led to the same conclusion: SRT is highly likely to be cost-effective. However, given that SRT was not cost-saving for the NHS over 12 months, future implementation research is needed to assess incentives for practices to implement SRT, as well as capacity considerations in relation to nurse delivery.
Strengths and limitations
The HABIT trial is the largest trial of SRT to date and one of the largest trials of psychological treatment for insomnia, yielding precise estimates of effect. It is the only trial to perform cost-effective analysis over a 12-month follow-up period. We conducted the trial across multiple general practices, across different regions of England, and trained nurses without formal experience of sleep intervention or psychological therapy to effectively deliver brief SRT with high levels of fidelity. This supports the generalisability of our intervention, while the brief training and delivery model speaks to scalability. We initially sought to only train practice nurses but due to availability issues at some practices we also trained additional research nurses to deliver treatment; however, they represented a minority (22.5%), and none of them had prior experience delivering sleep or behavioural treatment.
Retention was 85% overall at 6 months and 79% at 12 months, which is higher than previous primary care studies in the UK19,32 and broadly consistent with CBT-I studies over shorter follow-up periods.72 Participants in the treatment group were less likely to complete the primary outcome at all time points. We attribute this difference to the greater demands placed on participants in the SRT arm relative to SH with respect to scheduling of treatment sessions, recording of sleep diaries during the 4-week intervention phase, and (for some) the challenge and difficulties of following SRT instructions. Sensitivity analyses involving multiple imputation and covarying for baseline predictors of missingness yielded similar findings to the primary analysis. Indeed, even under conservative assumptions (i.e. models assuming high score differences between those with missing and non-missing ISI outcome), the conclusion remained the same. Although the pandemic affected the last 12 months of the trial, treatment adaptation was required for just 13 participants, and exploratory analysis of the 6-month primary outcome revealed no difference for pre versus during the pandemic. The pandemic also adversely affected our ability to collect data on sleep diary parameters, medication use, and actigraphy-defined sleep, and thus such analyses should be interpreted with caution given the low levels of outcome completion.
Our sample reflects the clinical reality of insomnia in that the majority of participants were female, had experienced insomnia for a long time (approximately 10 years), and had a range of comorbid conditions (89% had at least one comorbidity and 51% had three or more). Moreover, the majority had consulted their GP in relation to insomnia and 25% were taking prescribed sleep medication at baseline. However, our sample and results may not generalise to the entire UK insomnia population because participants tended to be well-educated (50% had a university degree), were more likely to be from a white ethnic background (97% of the sample), and live in areas with low levels of deprivation. These sample characteristics may, in part, be driven by greater than anticipated recruitment in Oxfordshire (which was unexpected but necessary to compensate for under-recruitment). There was, however, no evidence that the treatment effect was lower in people from more-deprived circumstances, but the analyses lacked power to detect such moderation. It was not possible to conduct such moderation analyses by ethnic group. Future trials should be informed by INCLUDE guidance and roadmap100 in order to improve representation of under-served groups and increase diversity of recruited participants.
Participants were not blind to treatment group and the primary outcome was self-reported insomnia severity; therefore, there is potential for bias in reporting. However, we did not reveal the hypothesis to participants (the study was set up as a test of two different sleep improvement programmes) and nurses were not involved in the collection of trial outcomes. We therefore believe that bias is unlikely to explain the results. In support of this, previous work has tested, and demonstrated superiority of, SRT against an active control condition matched for therapist time, support and implementation of behavioural sleep advice.24,25 A related point is that while SRT clearly out-performed SH, the SH group showed a reduction in ISI scores of approximately 3.5 points from baseline to 6 months. It is not clear what explains this reduction, but it may reflect regression to the mean, the natural course of insomnia over time, the effect of taking part in a study and/or the effect of SH.
Our approach to screening was automated and based on responses to questionnaires in order to assess for and exclude conditions that may not be suitable for SRT. We took this approach because it simulates a potentially scalable method that could be implemented in clinical practice, since primary care staff are not experts in sleep medicine. Nevertheless, without clinical interview or polysomnographic evaluation it is possible that some patients in the trial had undiagnosed sleep disorders, which plausibly could lead to a marginal dilution of the treatment effect.
Implications for health care
Our trial shows that nurses can be trained to deliver a focused and manualised behavioural insomnia treatment, leading to patient benefit, and without safety concerns. Moreover, the intervention is very likely to be cost-effective. Nurse-delivered SRT could therefore become part of primary care management of insomnia. At present, patients are typically provided with SH advice or sedative medication. NICE guidelines recommend that patients with insomnia are offered CBT-I as the first-line treatment, but there is limited access to psychological treatment for insomnia, with the exception of a few specialist clinics or services, or digital CBT implementation projects. The European Academy of CBT for insomnia articulates a vision ‘to develop services in such a way that CBT-I becomes available at a scale equivalent to medication’ and emphasises GP intervention and digital CBT.101 There are practice nurses in every GP surgery (approximately 23,000 practice nurses across England) who may have the capacity to support people with insomnia using behavioural therapy, consistent with other clinical activities like weight management and smoking cessation. This is likely to result in a shift of consultation from GPs to practice nurses. Nurses and practice managers in the HABIT trial considered it to be feasible and had additional suggestions for implementation, including group sessions and enhanced flexibility in scheduling appointments. Nurse-delivered treatment could complement initiatives to increase access to digital therapies and cater for those who prefer face-to-face contact with a health professional – indeed qualitative interviews emphasised the importance of face-to-face sessions for SRT engagement. Those who do not achieve sufficient response to nurse treatment could then be reviewed by the GP and, if appropriate, referred to a specialist in sleep.
It is also possible that this treatment with its brief training and delivery model could be incorporated into the Improving Access to Psychological Therapies (IAPT) service in England. Most people with depression and anxiety, the main conditions treated within IAPT, experience insomnia symptoms and our data show improvement in PHQ-9 and SF-36
MCS scores. Thus, our sleep treatment package may improve outcomes for many patients in IAPT programmes. Finally, beyond UK health care, brief nurse-delivered behavioural treatment could widen access to evidence-based intervention in developing countries where there are limited dedicated mental health provision and barriers to digital engagement.
Recommendations for future research
Below we summarise specific research areas that should be followed up in future studies to build on the findings of the HABIT trial:
Formally investigate the integration of nurse-delivered
SRT into the insomnia management pathway in primary care, for example as part of a stepped-care framework.
Assess generalisability of results across diverse primary care patients with insomnia.
Investigate additional methods to support patient engagement with treatment.
From a health economics perspective, investigate practice incentives for adopting
SRT, including practice nurse capacity.
Investigate the effects of nurse-delivered
SRT in specific subgroups, for example long-term hypnotic users, people with mental health problems, those presenting with insomnia for the first time.
Conclusions
Brief nurse-delivered SRT in primary care is clinically effective for insomnia disorder, safe, and likely to be cost-effective. SRT could become part of a stepped care approach to insomnia treatment, helping to facilitate the implementation of NICE guidelines and increase access to evidence-based intervention.
