Sleep Disorders and Sleep Deprivation: An Unmet Public

Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem
http://www.nap.edu/catalog/11617.html
CONSEQUENCES OF CHRONIC SLEEP LOSS AND SLEEP DISORDERS 59
changes. Adults are sleeping less to get more work accomplished and are
staying up later to watch television or use the Internet (NSF, 2005b).
Sleep Loss Affects Health
In the past 10 or more years, research has overturned the dogma that
sleep loss has no health effects, apart from daytime sleepiness. The studies
discussed in this section suggest that sleep loss (less than 7 hours per night)
may have wide-ranging effects on the cardiovascular, endocrine, immune,
and nervous systems, including the following:
• Obesity in adults and children
• Diabetes and impaired glucose tolerance
• Cardiovascular disease and hypertension
• Anxiety symptoms
• Depressed mood
• Alcohol use
Many of the studies find graded associations, insofar as the greater the
degree of sleep deprivation, the greater the apparent adverse effect (although
the difference may not reach statistical significance). Another common finding
is the relationship that adverse effects occur with either short or long
sleep duration, as compared to a sleep time of 7 to 8 hours. This type of
association is often described as a U-shaped relationship. It should be noted,
however, that the majority of these studies are observational in nature, and
thus definite causal inferences cannot be made. The associations observed
in some studies might be subject to different types of biases, such as temporal
(or “reverse causality”) bias, whereby sleep loss might be a manifestation
or a symptom of the disease in question. The latter is most likely in
cross-sectional studies but could also affect associations observed in cohort
studies, particularly when they are relatively short term and/or when the
disease under investigation has a long preclinical phase. In the discussion
that follows, and wherever possible, potential physiological mechanisms
behind epidemiological associations and that support the plausibility of a
true causal relationship are noted.
Sleep Loss Is Associated with Obesity
When a person sleeps less than 7 hours a night there is a dose-response
relationship between sleep loss and obesity: the shorter the sleep, the greater
the obesity, as typically measured by body mass index (BMI)—weight in
kilograms divided by height in meters squared. Although most studies were
cross-sectional, one prospective study was a 13-year cohort study of nearly
Copyright © National Academy of Sciences. All rights reserved.