I wrote a first post last month about a workshop I went to given by Professor Colin Espie - "Sleep well and live better: overcoming insomnia using CBT".  I mentioned that he went through the sequence: What is insomnia?  Why is it a big deal?  Why is cognitive behaviour therapy relevant?  Is it clinically effective?  How can it be delivered in real world practice?  In today's post I would like to look more at Why is it a big deal?  And I would like particularly to focus on links between insomnia and depression. 

• Current insomnia is a major risk factor for subsequent depression, as well as for a series of other health problems.  In a recent systematic review - "Insomnia as a predictor of depression: A meta-analytic evaluation of longitudinal epidemiological studies" - Baglioni & colleagues identified and assessed 21 relevant research papers.  They concluded "Non-depressed people with insomnia have a twofold risk to develop depression, compared to people with no sleep difficulties.  Thus, early treatment programs for insomnia might reduce the risk for developing depression in the general population and be considered a helpful general preventive strategy in the area of mental health care."  Current sleep problems sadly are also associated with increased risk of developing a series of other health issues as well.  Salo et al. - "Sleep disturbances as a predictor of cause-specific work disability and delayed return to work" - followed up nearly 57,000 subjects for over 3 years and found initial sleep disturbance on most nights of the week predicted greater likelihood of subsequent extended time off work from any of a variety of problems - mental disorders, circulatory disorders, musculoskeletal symptoms, nervous system, and injuries.  This link between current insomnia and subsequent long-term disability is a strong one, so the authors of "The long-term effect of insomnia on work disability: the HUNT-2 historical cohort study" reported that "Insomnia was a strong predictor of subsequent permanent work disability ... and this association remained significant after adjustment for psychiatric and physical morbidity and for health-related behaviors."

• Suffering from both insomnia and depression is associated with more severe depression.  In a further major recent paper assessing nearly 4,000 depressed people - "Insomnia in patients with depression: a STAR*D report" - it was found that 85% also suffered from current insomnia. Depression with sleep problems was more severe than the much less common depression without sleep problems.  Another large study - "The relationship between depression and sleep disturbances: a Japanese nationwide general population survey" - reported that "Those whose sleep duration was less than 6 hours and those whose sleep duration was 8 hours or more tended to be more depressed than those whose sleep duration was between 6 and 8 hours. Thus, sleep duration exhibited a U-shaped association with symptoms of depression.  As subjective sleep sufficiency (self-rating of sleep adequacy) decreased, symptoms of depression increased, indicating a linear inverse-proportional relationship.  Conclusion: The fact that sleep duration and subjective sleep sufficiency exhibited different relationships with symptoms of depression indicates that these 2 sleep parameters each have their own significance with regard to depression."  It's worth noting here that a diagnosis of "insomnia" involves not only criteria about time spent sleeping but also that "the sleep disturbance (or associated daytime fatigue) causes clinically significant distress or impairment in social, occupational, or other important areas of functioning".  There is interesting research suggesting that short sleep duration on its own, without linked distress or impairment, may not be much of a mental/physical health risk - see, for example "The effect of short sleep duration on coronary heart disease risk is greatest among those with sleep disturbance".  As a happy but somewhat 'short duration' sleeper myself (part of what allows me to write this blog!), I look forward to more research emerging on this latter point.

• When people recover from depression, they are often left with persisting sleep difficulties.  There are a number of, mostly smaller, research studies suggesting that this continuing insomnia is associated with an increased chance of the depression returning.  A number of research teams have demonstrated this link - see "Which symptoms predict recurrence of depression in women treated with maintenance interpersonal psychotherapy?", "Sleep disturbance and depression recurrence in community-dwelling older adults: A prospective study" and "Residual symptoms and recurrence during maintenance treatment of late-life depression".  However there is other work throwing some doubt on the association - "Residual symptoms after remission of major depressive disorder with citalopram and risk of relapse: a STAR*D report".  This caution over how important persisting insomnia is as a risk factor for depressive recurrence, does not take away from the broader injunction to try to treat depression to full recovery, not least because subclinical ongoing symptoms like anhedonia, feelings of worthlessness, psychomotor agitation/retardation & mood disturbance do seem strong predictors of relapse risk - see "Sleep complaints and depression in an aging cohort: A prospective perspective". 

• The links between insomnia and depression aren't simply due to a straightforward cause-effect sequence.  We know that sleep difficulties are associated with 1.) an increased risk of developing subsequent depression.  2.) increased severity of depression.  3.) probably an increased risk of depression returning after recovery.  These connections are multifactorial.  Riemann & colleagues, in their paper "The hyperarousal model of insomnia: a review of the concept and its evidence", have written "The current review provides substantial support for the concept that hyperarousal processes from the molecular to the higher system level play a key role in the pathophysiology of primary insomnia.  Autonomous, neuroendocrine, neuroimmunological, electrophysiological and neuroimaging studies demonstrate increased levels of arousal in primary insomnia during both night and daytime.  In the light of neurobiological theories of sleep-wake regulation, primary insomnia may be conceptualized as a final common pathway resulting from the interplay between a genetic vulnerability for an imbalance between arousing and sleep-inducing brain activity, psychosocial/medical stressors and perpetuating mechanisms including dysfunctional sleep-related behavior, learned sleep preventing associations and other cognitive factors like tendency to worry/ruminate."  So insomnia can be helpfully viewed as caused by this triad of underlying genetic vulnerability, current psychosocial/medical stressors, and dysfunctional cognitive/emotional/behavioural responses.  In fact, there's probably an even better/fuller explanation provided by a generic diagram I use a lot when responding to someone's query as to why they have developed a persisting distressed state like ongoing depression and/or anxiety.  So one of the several links between depression and sleep difficulty is due to a shared genetic predisposition - see "Associations between sleep quality and anxiety and depression symptoms in a sample of young adult twins and siblings".  As an aside I would comment that it is perfectly possible to reduce the toxic effects of someone's increased genetic risk.  An example is provided by the recent paper "Physical activity attenuates the genetic predisposition to obesity".  Another insomnia/psychological state link is bi-directional with current stress increasing the likelihood of developing insomnia, while in parallel insomnia increases the likelihood of becoming more stressed - see, for example, the paper "On the nature of burnout-insomnia relationships: a prospective study of employed adults."   And thirdly one's reaction to sleep difficulty may then either minimise or aggravate the problem.  This finding is of particular relevance to subsequent posts on the value of cognitive therapy for insomnia.  So unhelpful beliefs about sleep predispose to developing sleep problems, aggravate insomnia once it is present, and can interfere with treatment benefits.  Research highlighting these points includes "A penny for your thoughts: Patterns of sleep-related beliefs, insomnia symptoms and treatment outcome", "Residual sleep beliefs and sleep disturbance following cognitive behavioral therapy for major depression" & "Are changes in beliefs and attitudes about sleep related to sleep improvements in the treatment of insomnia?" 

I intend to write more on insomnia and cognitive therapy soon.