"As early as 1964, data have shown that 7-h sleepers experience the lowest risks for all-cause mortality, whereas those at the shortest and longest sleep durations have significantly higher mortality risks. Numerous follow-up studies from around the world (e.g., Japan, Israel, Sweden, Finland, the United Kingdom) show similar relationships. "
"Over 40 years of evidence indicate a strong association between nightly sleep duration and mortality risk.1,2 In general, sleep duration is associated with mortality in a U-shaped fashion, such that the lowest risk is most often found in the group who report sleep durations of 7–8 h"
"The first study to examine the relationship between sleep duration and mortality risk in the population was reported in 1964.3 Those reporting 7h of sleep demonstrated the lowest mortality rate."
"A series of subsequent investigations analyzed data from adults from the Alameda County Study.5–9 Mortality rates were calculated for a 9-year follow-up period adjusted for up to 14 covariates in addition to age."
"In a later analysis, Kaplan et al.8 analyzed age groups separately with a 17-year follow-up. In this analysis, a significant increase in mortality for the <7 h and >8 h sleepers was only present for those aged 50–59 at the time of follow-up."
"While previous literature clearly describes an association between mortality and both short and long sleep, the remainder of this review will focus on mechanisms and pathways primarily associated with only short sleep, as short and long sleepers seem to represent distinct groups.41 Effects for long sleep may be larger, but we chose to focus on short sleep for two reasons. First, shorter sleep appears to be a more salient issue in our society where insufficient sleep is a major public health concern.42
Furthermore, large numbers of laboratory studies support mechanisms that may explain a direct link between short sleep and mortality. Thus, short sleep is a more wide-reaching problem with a larger base of research from which to draw conclusions. Second, a fairly comprehensive review of mortality associated with long sleep, and possible mechanisms, was recently published.1 We wished to avoid redundancy with that publication, taking advantage of limited space by only addressing short sleep."
"Short sleep is related to cardiovascular disease, cancer, cerebrovascular accidents, diabetes, and hypertension. These associations may occur via metabolic or inflammatory processes, physiologic stress, or socioeconomic factors."
"Sleep duration and mortality are related in a U-shaped fashion with the lowest risk being about 7–8h and increasing risk associated with more or less sleep. This relationship holds true across the adult lifespan, various geographic regions, and with the inclusion of a variety of covariates."
Ref.: Grandner et al. 2010
Thanks to Lars Avenmarie for the infographic and evidence based study.