Health effects of Sleep Disturbances
Sleep has a significant effect on health. Many studies have investigated the effect of shorter than desirable sleep duration and other sleep disturbances on morbidity and mortality risk. Nevertheless, it should be noted that reverse causality may exist, whereby medical conditions and various behaviors raise the likelihood of sleep disturbances rather than resulting from sleep disturbances
Effect of Sleep Disturbances on Morbidity
Sleep deprivation and other sleep disturbances may affect the cardiovascular system. A meta-analysis which included seven studies performed between 1997-2009 found an increased risk of developing cardiovascular disease or death from cardiovascular causes amongst those who slept for less hours than desirable (1.48 times increased risk) or for many more hours than desirable (1.38 times increased risk). Risk of developing cardiovascular disease or dying from cardiovascular causes was also found to be significantly increased (1.45 times increased risk) amongst people suffering from insomnia.
Sleep deprivation was also found to be related to increased risk (by 21-23%) of hypertension. Short or long sleep duration were related to increased risk of stroke or dying from stroke, but it is noted that not all the studies found a positive association between sleep disturbances and cardiovascular events.
Studies have shown an association between sleep deprivation and weight problems. Shorter than desirable sleep and greater food consumption are related to behavior causing weight gain, such as little physical activity. Lab studies proposed that short sleep duration might also affect weight gain via metabolic or hormonal pathways. Growth hormone is released during deep sleep and therefore chronic short sleep in childhood also affects growth.
Sleep phase postponement affects the Circadian rhythm and suppression of the hormone melatonin (“sleep hormone”) which is related to control of malignant processes. Epidemiological studies have found that working at night increases the risk of cancer. In 2007 the International Agency for Research on Cancer – IARC (a World Health Organization agency) designated work at night (people who work and are exposed to light during the hours when it is dark) as probably carcinogenic to humans – Group 2A (meaning that there is limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in animal experiments).
Sleep disturbances may also cause increased risk of infectious diseases and inflammatory processes, and there is even an opinion that sleep disturbances affect the immune system and perhaps thus also affect morbidity. It should be noted that not all the studies support these hypotheses and that the precise mechanism whereby sleep or its deprivation might affect the various body systems are not certain.
Effect of Sleep Disturbances on Mortality
Studies have shown that shorter or longer than desirable sleep duration are related to increased mortality. In a meta-analysis that included 16 articles (from 1993-2009) it was found that short sleep duration is related to statistically significant increase in mortality risk (1.12 times greater), while longer than desirable sleep duration is related to 1.3 times greater mortality risk. It is possible that the association is mediated by diseases and physical problems such as heart disease, diabetes etc. which affect sleep and are known causes of mortality.
Effect of sleep disturbances on psychological and cognitive health
An association has been found between sleep disturbances and rate of psychological problems or their degree of severity. Several studies have shown that insomnia is related to higher frequency of clinical depression and anxiety disorders amongst adolescents. It has been found that sleep problems can affect the mental state of both children and adolescents. Short sleep duration or sleep disturbances have been found to be related to suicide attempts and suicidal thoughts in adolescents. Children whose parents allowed them to go to sleep at midnight or later were at greater risk of developing depression or suicidal thoughts than children whose parents who fixed their bedtime at 22:00 or even earlier.
Amongst children and adolescents shortening of sleep duration can cause daytime sleepiness which leads to falling asleep during classes, impaired concentration, memory and decision making and drop in academic performance at school. Performance of tasks requiring prolonged concentration and those requiring abstract or creative thinking, is particularly affected by insufficient sleep. Similarly, motor skills and reaction time can be impaired by sleep disturbances.
Dangerous behavior amongst those suffering from sleep disturbances
Lack of sleep increases the risk of road accidents, which are one of the main causes of death amongst adolescents.
According to data from the Israeli “Green Light” non-profit association, the fatigue factor is involved in about 20% of fatal accidents in the world. Fatigue causes, amongst other things, drop in alertness, prolonged reaction time and less efficient information processing – which are important for carrying out the tasks related to safe driving. In addition, an association was found between reduced sleep quality in adolescents and risk of smoking and alcohol consumption, but the direction of this association is unclear.
*This review was prepared with the assistance and guidance of Prof. Tamar Shochat, The Faculty of Social Welfare and Health Sciences, Haifa University and Mr. Amit Green from the Assuta Health Center Sleep Institute.
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