Compared to the amount of data available from laboratory and epidemiological studies, there has been relatively little investigation of verified short sleepers. However, given the findings from these domains, several patterns emerge:
First, short sleep has been associated increased mortality risk. While the risk associated with long sleep may be greater, self-reported short sleep does carry an increased risk, which is unexplained by cancer and cardiovascular events, even though short sleep may be a risk factor for heart attack and stroke. The mortality relationship is a global issue, as studies from 5 decades and several countries have replicated this finding. Sleep may be directly related to mortality, or, more likely, it may mediate or moderate a relationship involving cardiovascular disease, obesity, metabolic dysregulation, stress, immune dysfunction, psychological health, cancer or coping difficulties. Laboratory results suggest that sleep deprivation is associated with impairments in these domains, and epidemiological studies confirm that short sleepers report impaired overall health as well as a number of cardiovascular and metabolic risk factors that support that this pattern may be seen in habitual short sleep. However, future studies need to link the laboratory findings and epidemiological results to verified short sleepers, so that the extent of the presence of these risks in this group is understood.
Second, short sleep has been associated with metabolic dysregulation and obesity. Sleep deprivation has been shown to produce short-term changes in a number of endocrine systems, including insulin, glucose, leptin and ghrelin. These differences may persist over the long term, explaining some of the epidemiological finding. Also, short sleepers may be more likely to eat higher-fat foods, which may be causing the obesity repeatedly demonstrated in epidemiological studies and may or may not be driven by endocrine changes.
Third, short sleep has been associated with worse cardiovascular health. While this has primarily been driven by epidemiological studies, with their inherent problems with the measurement of sleep (described below), the evidence suggests that those reporting less sleep are at greater risk of hypertension, stroke and myocardial infarction than those who sleep 7–8 hours. This relationship may be greater in women than men, and may be evident for long sleep as well. This is supported by a number of laboratory studies that suggest that sleep deprivation is associated with heightened blood pressure and sympathetic activity67–68
Fourth, short sleep has been associated with impaired neurobehavioral performance and cognitive functioning. These results have been primarily explored in the context of sleep deprivation studies and have not been replicated in naturalistic settings. It is unclear whether performance deficits associated with short-term sleep deprivation describe the experience of habitual short sleepers. These results are supported by epidemiological findings, which suggest that short sleepers report more sleep disturbance, including daytime sleepiness98
Fifth, short sleep has been associated with psychological/psychiatric disturbances and poor general health. Sleep deprivation studies show that at least short term neurophysiological changes indicative of stress and depressive symptoms result from sleep deprivation. Studies of self-reported short sleepers mirror these findings, showing that short sleepers exhibit more risk factors for stress and depression, as well as characteristic coping styles.