Essential Sleep (Part 6). Cognitive decine and the brain

Cognitive decline

Impaired sleep function decreases the neuroplasticity in the CNS resulting in diminished cognitive function as impulse transmission are impaired (Vance et al. 2010). Sleep is the regenerative time for the CNS and nerves, without which brain atrophy and weakened conduction can result.

Increasing studies have found an association between poor sleep and cognitive decline. A link between poor sleep quality and the development of cognitive decline over three to four years was found in a new study of older men. Results show that higher levels of fragmented sleep and lower sleep efficiency were associated with a 40 to 50 percent increase in the odds of clinically significant decline in executive function, which was similar in magnitude to the effect of a five-year increase in age. In contrast, sleep duration was not related to subsequent cognitive decline. It was the quality of sleep that predicted future cognitive decline in this study, not the quantity (Blackwell, et al 2014 ).

Research on sleep deprivation suggests that the result of missing an entire night of sleep is equal to an IQ drop of ten points.  This IQ drop was even more significant in men who took part in the tests than in women.  Symptoms of sleep deprivation include constant yawning, the tendency to doze off when not active for a while (for example, when watching television), grogginess when waking in the morning, sleepy grogginess experienced all day long (sleep inertia), lack of ability to concentrate and moodiness. In a study of 1,793 participants (51% men; 63.8±7.5 years) found that poor sleep quality SDB, is associated with Mild Cognitive Impairment. (Martha Dlugaj, et al Sleep-Disordered Breathing, Sleep Quality, and Mild Cognitive Impairment in the General Population).

Tired brains

Brains that are sleep deprived aren’t as efficient have to work harder. studies show the brains of the sleep deprived desperately pumping energy into the prefrontal cortex, trying to overcome the effects of sleep deprivation.

Long-term memory

Sleep plays an important role in consolidating memories. While we sleep, our brain orders, integrates and makes sense of things that have happened to us. Not only that, but we seem to consolidate our learning while we sleep. Without sleep the process is badly disrupted, meaning it’s difficult to lay down long-term memories and it’s harder to learn new skills.


Sleep deprivation causes many of the powers of focus and attention to decline which partly explains

distracted feeling you get when tired.

Planning and coordination

Planning and coordination declines dramatically with lack of sleep. Sleep deprived people easily get stuck in thinking loops and as a result fall back on the brain’s automated systems, our habits.

Mental illness

A wide range of health effects are associated with poor sleep including a raft of psychological conditions including depression, stress and  anxiety. Sleep deprivation on a regular basis increases the experience of mania, including psychosis, paranoia, extremely high energy levels, hallucinations, aggression and more. Links have been found between insomnia and mental illness. Unfortunately mental illness can also cause poor sleep.

There is a large amount of evidence of a high rate of comorbidity between sleep disorders and various psychiatric illnesses, especially mood and anxiety disorders. The disturbance of sleep quality and continuity that is associated with many sleep disorders predisposes to the development or exacerbation of psychological distress and mental illness. Likewise, the presence of psychiatric illness may complicate the diagnosis and treatment of sleep disorders. The data not only underscore the high frequency of psychopathology and psychological distress in sleep disorders, and vice versa, but also suggest that combined treatment of both the mental disorder and the sleep disorder should become the standard for effective therapy for all patients (Sateia, 2009)

Sleep related  major psychiatric disorders: alcohol dependence, schizophrenia, depression and anxiety disorders. many studies have been conducted about the relationship between sleep and depressive symptoms, including reporting that shorter sleeping time and poorer subjective sleep quality is associated with higher a risk of depressive symptoms. Ina study of 2,643 full-time employees (1,928 men and 715 women), aged 18-79 years (mean = 45 years), in small- and medium-scale businesses participants working > 10 hours per day, sleeping < 6 hours per day, and reporting insufficient sleep were, respectively, 37%, 43%, and 97% more likely to be depressed than those working 6 to 8 hours per day, sleeping 6 to < 8 hours per day, and reporting sufficient sleep (P < .05). Participants working > 10 hours per day or > 8 to 10 hours per day with < 6 hours per day of sleep showed a 41%-169% higher prevalence of depression versus those working 6 to 8 hours per day with 6+ hours per day of sleep (P < .05). Participants reporting insufficient sleep in 3 work-hour categories (6 to 8, > 8 to 10, and > 10 hours per day) showed a 62%-179% increase in the prevalence of depression versus those working 6 to 8 hours per day and reporting sufficient sleep (P < .05). No significant effects on depression were found for subjects in any work-hour category with 6+ hours of sleep or with subjective sufficient sleep. Depression associated with long work hours is primarily a result of sleep deprivation (Nakata 2011.  2011).  In a study of 4,833 female workers in the manufacturing, finance, and service fields Job stress and sleep quality were strongly associated with depressive symptoms. In particular, the lack of reward and subjective sleep factors are the greatest contributors to depression (Ho-Sung Cho, Young-Wook Kim, et al 2013).

In a survey of 24,686 individuals aged 20 years or older 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 decreased, symptoms of depression increased, indicating a linear inverse-proportional relationship. 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 (Kaneita et al 2006). 

Similarly in a survey of 99,668 adolescents mental health status of subjects whose sleep duration was less than 7 hours, and those who slept 9 hours or more, was poorer than that of subjects who slept for 7 hours to 9 hours. A U-shaped association was observed between mental health status and sleep duration. Furthermore, a linear association was observed between subjective sleep assessment and mental health status; the worse the subjective sleep assessment, the poorer the mental health status. Mental health status was also inversely proportional to the frequency of insomnia symptoms. The fact that sleep duration and subjective sleep assessment showed different patterns of association with mental health status indicates that these 2 sleep parameters have independent significance (Kaneita et al 2007 ). Association between mental health status and sleep status among adolescents in Japan: a nationwide cross-sectional survey).

 In a study of 516 students with a mean age of 13 years the incidence of newly developed poor mental health status during the 2 years leading to the follow-up study was 35.1%. New onset of poor mental health status was significantly associated with new onset of sleep disturbance and lasting sleep disturbance. The incidence of sleep disturbance during the 2 years leading to the follow-up study was 33.3%. New onset of sleep disturbance was significantly associated with new onset of poor mental health status and lasting poor mental health status. Sleep disturbance and poor mental health status increase each other's onset risk (Kaneita et al 2009).

Considering these associations, it is important to promote mental health care and sleep hygiene education together.

Brain damage

Sleep deprivation damages brain cells. One recent study found that in mice 25% of certain brain cells died as a result of a prolonged lack of sleep.


Part 7 coming