Sleep Disturbance: The Silent Killer

A bad night’s sleep can be frustrating for many reasons, but we rarely consider its impact beyond the associated fatigue or the sluggish day of work. Sleep deprivation is associated with both short and long term health concerns, and the evidence is only mounting. From a very basic standpoint, poor sleep makes us less cognitively sharp and therefore at a greater risk for careless mistakes. This is consistent with many studies finding that self-reported sleep problems, short sleep duration, fatigue and daytime sleepiness are all linked in some way to workplace injuries due to accidents.1

Nevertheless, what about the health impact of inadequate sleep beyond injury? Well, surveys taken by insomniacs have shown impairments in physical functioning, pain measures, social functioning and emotional health.2-4 Insufficient and excess sleeping duration have been associated with an increased risk of all-cause death by as much as 12% and 30%, respectively!5 In AOR’s Advances: Stress (Part 1) magazine, we thoroughly examined the sleep cycle, basic sleep physiology, common causes of sleep disturbances, and natural sleep aid remedies (visit www.aor.ca/magazines for previous Advances issues). Here we take a look at how sleep deprivation and poor sleep habits can negatively impact all aspects of our health.

While the mechanisms responsible for sleep deprivation’s negative health consequences are still being investigated, it appears that they derive from key themes: endocrine disruption and metabolic dysregulation.6 Basically this means that there are alterations in hormone output and our body’s ability to break down and synthesize molecules, for example, for energy production and waste excretion. In healthy sleepers, growth hormone (GH) is released at nighttime and cortisol is not. In problem sleepers, the opposite is true.7 Impaired glucose tolerance, decreased insulin sensitivity, proinflammatory cytokines and low-grade inflammation (measured by an increase in C-reactive protein) are also all associated with impaired sleep.8 These factors, in combination, seem to contribute to or at least aggravate a large number and wide variety of health concerns. Given the underlying pathological process of something like inflammation in so many chronic diseases (including cardiovascular disease, diabetes and cognitive impairment), it’s no surprise that such associations exist. See Box 1 for a quick look at some of the health conditions that have been associated with poor sleeping patterns.

Cardiovascular and Coronary Heart Disease

When most people think about cardiovascular disease (CVD), they consider lack of exercise and poor diet; poor sleep habits hardly ever enter the conversation. Yet, new research is uncovering the strong association between cardiovascular events and sleep disturbances. A 2012 meta-analysis found that insomnia was associated with a 45% increased risk of death and disease from CVD.9 Given that heart disease is the number one leading cause of death in Canada and the United States,10,11 it may be time to start fixing the North American sleep pandemic.

A 2013 study examined this connection between coronary heart disease (CHD) and sleep characteristics in over 86,000 postmenopausal women.12 Specifically, sleep duration and sleep quality were assessed (i.e. how often were the women waking throughout the night, trouble falling sleep, etc.). After a 10-year follow-up period, it was discovered that women who slept the least (less than 5 hours/ night) had a much higher number of CHD and CVD events. Interestingly, those who overslept (greater than 10 hours/night) were associated with an even worse cardiovascular prognosis!12

While these findings were substantial, it’s crucial to note that they were not the only discoveries. Poor sleep quality (as opposed to duration) was predictive of CVD events too, and sleep deprivation also comes with a greater risk for high blood pressure measurements!13 These associations have not just been found in female populations. In fact, both insomnia and short sleep duration were found to be associated with a 4-times greater risk of death in men according to one study.14 Researchers have determined that the mechanisms most likely responsible for this cardiovascular damage are increased sympathetic nervous system activity, disturbed immune function and increases in inflammation.15

Regardless of the mechanism, if insomnia and abnormal sleep duration increase the risk for CHD and CVD, then interventions that improve sleep quality and normalize sleep duration should serve as top priority treatment interventions.16

Diabetes and Obesity

In the same large-scale study examining over 86,000 postmenopausal women and their risk of CVD, a significant finding was noted regarding the incidence of diabetes. Independently, a strong association between lack of and excess sleep was discovered with diabetes risk too!12 While this is hardly the first time researchers have made this connection, it is definitely one of the largest studies of its kind.

As we saw with the increased risk of CHD and CVD, sleep deprivation’s association with obesity and diabetic risk appears to be just as complex and multifactorial. Glucose dysregulation, insulin resistance, leptin inhibition and proinflammatory cytokine production all reasonably contribute to increased risk of obesity and diabetes, yet many negative behavioral habits tend to coexist as well.17-19

Shorter sleepers and longer sleepers have been shown to engage in less physical activity20 and watch more television than average sleepers.21 When we combine this with the fact that even a single night of sleep deprivation (4 hours) has shown to lead to increased food consumption during the subsequent day (on average 559 more calories, or approximately 22% more of their daily energy consumption),22 we have a recipe for disaster. Subjective hunger levels before dinner and breakfast have also been noted to be higher in those with acute sleep deprivation on the night prior.22

In summary, sleep disturbances lead to less exercise, increased hunger and greater food consumption. Knowing this, is it any surprise that shorter and longer sleep durations have also been associated with higher body mass and greater abdominal fat?23, 24


Mood disorders, such as depression and anxiety, have long been associated with insomnia. It seems intuitive that when people are depressed or anxious, they tend to sleep worse. However, recent research has shown that the reverse association is also likely to be true; poor sleeping patterns and habits greatly increase the risk of mood disorders. In the case of depression, this increased risk has been found to be as much as five times greater with problem sleepers. Difficulty falling asleep, difficulty returning to sleep and decreased sleep duration all predicted greater depression outcomes.25

Once again, the large-scale study of over 86,000 women found a U-shaped association with sleep and depression (meaning excess and lack of sleep increase the risk of depression, just as they did with CHD and diabetes).12 In addition, a more focused study found the same connection. 555 men and women underwent insomnia labs and questionnaires and were ultimately selected based on the criteria of having no prior history of depression. Within a follow-up period of four years, 26 of these individuals developed clinical depression and, as predicted, these individuals had the worst sleeping habits.25 Perhaps the scariest discovery regarding the association between insomnia and mood disturbance is the finding that the greater risk for subsequent depression lasts for decades! Insomnia in young men was found to increase the risk for subsequent clinical depression and psychiatric distress for at least 30 years.26

In response to these findings, some researchers and practitioners have suggested that sleep disturbances are a prodrome to depression, meaning that insomnia can be viewed as an early symptom of depression. In this sense, treatment of sleep deficits is imperative for prevention of mood disorders.25

Impaired Bone Health

Healthy bones need calcium – but they also need sleep. Numerous studies have demonstrated that irregular sleep patterns may have detrimental impacts on bone health. One study in over 600 Chinese women found that shorter sleep duration was associated with decreased total bone mineral density (BMD) and regional BMD in those over the age of 45.27 Significant impairments in bone health were seen in those women sleeping less than six hours per night.

In this scenario, researchers conclude that the decreased BMD discovered in those with less sleep is most likely due to the corresponding elevations in cortisol during the daytime.27 In other words, stress can cause sleep deprivation and sleep deprivation can cause stress. This forms a vicious cycle of elevated cortisol that is capable of inhibiting bone formation via two methods: bone formation is inhibited through suppression of bone marrow cell production, and osteoclasts (cells that breakdown bone tissue) go from intermittent activity to full-time destroyers.27 Proinflammatory cytokine activation, once again, cannot be ruled out as a prime culprit in this mechanism of destructive bone processes!28

Impaired Immune Function

Some very interesting research has demonstrated that the disruption of our sleep-wake cycle can lead to long-lasting compromised immune function. Generally speaking, this is because our immune system is repaired while we sleep; activation and proliferation of many immune cells have been shown to exhibit the greatest activity at nighttime.29 When our body cannot dedicate energy toward these immune building activities, we leave ourselves vulnerable to infections.

One study recorded the sleep habits of 155 healthy individuals over 14 days before administering nasal drops of the rhinovirus (the virus most commonly responsible for the common cold).30 Upon follow-up, it was discovered that people who slept for an average of less than seven hours per night were 2.94 times more likely to develop a cold than those who slept more than eight hours per night. Poor sleep quality (measured as less than 92% of time in bed actually spent sleeping) led to a 5.5 times increased likelihood of contracting a cold when compared to efficient sleepers (greater than 98%).30 Sleep also enhances the formation of our immune system’s memory, meaning tonight’s sleep can affect your body’s ability to fight off an infection months from now!31 A very interesting study examined the effect of sleep deprivation after the hepatitis A vaccine administration. Subjects that slept regularly on the first night following vaccination showed twice the levels of Hepatitis A antibody in their blood samples four weeks later, as opposed to those who stayed awake for the duration of that first night.31 This immuno-enhancing effect of sleep was still present at a 1-year follow-up!

What You Need to Know

The take home message here is that there are many reasons why seven to eight hours per night of quality sleep is recommended. Poor sleep leads to a brittle-boned, depressed, overweight, injury-prone and overall sicker version of yourself. As with most things in life, moderation and consistency are healthy habits and research supports this idea when it comes to sleep.

The research provides a reasonable argument that sleep quality and quantity should always be evaluated and monitored when treating any illness. Reduce your stress levels, maintain a healthy weight and make sleep a priority for your health. If necessary, consider gentle and effective natural health products to promote relaxation and ensure high quality sleep of adequate duration. Above all, regardless of the cause (i.e. restless leg syndrome, anxiety, stress, sleep apnea, etc.) it is well worth the investment to ensure a consistent good night’s sleep.

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