Conversely short and long SD

Conversely, short and long SD could be a result of poor SRH. One third of the older adult population has extreme SD (short or long) and presents difficulties in sleep onset and maintenance or has daytime sleepiness [7,26]. A prospective observational study of adults ages 40–64 found no evidence that SD is associated with SRH in either subjective or actigraphic measures [27]. Studies involving middle-aged and elderly participants have documented adverse effects for both short and long SD, although they are related to different health outcomes [28,29]. In this review, we found the SD–SRH interaction in 2 studies with this population [22,30], suggesting that long SD predicts worse SRH. Magee et al. [22] stratified the analysis by age and found that for participants between the ages of 45 and 74 years, short (<6h) and long (≥9h) sleep were associated with SRH; participants aged 75–84 had only long sleep associated with SRH in the adjusted analysis; and finally, participants between the ages of 85 and 97 did not show these correlations even in the unadjusted models. In fact, while much is known about the negative impacts in insufficient sleep, very little is known about the risks associated with long sleep duration. Long sleep is defined as a habitual sleep length of at least 9h, except hypersomnia as a clinical condition, and a long sleep duration may be associated with an increased mortality hazard caused by factors such as sleep fragmentation (excessive time in bed, wake after sleep onset and delayed sleep latency); fatigue and lethargy; immune function (long sleep may influence the increase of cytokine expression); photoperiodic abnormalities (long periods of time in a darkened environment); lack of challenge (longer time in bed provides fewer opportunities for experiencing stressors, offering physiological changes); and depression or underlying disease process (sleep apnea, order SGC707 disease, failing health). Additionally, these factors may also be related to each other [31]. In a self-reported habitual long sleep duration study in the Nurses Health Study II, Patel et al. [32] found that long sleepers reported an increased likelihood of a history of depressive symptoms, antidepressant use, benzodiazepine use, lack of physical activity, never married or divorced status, living alone, lower income, unemployed status and lower social status. Finally, mortality risks of long sleepers may be associated with general failing health. Specifically, Kakizaki et al. [23] found an association between stroke mortality and SRH in long sleepers. In this sense, the possibility of poor health leading to longer sleep duration seems more plausible than the alternative. Long sleep is more prevalent in those over 60 years old [7], thus leading to excessive daytime sleepiness [33]. On the other extreme, Steptoe and colleagues [17] expected that SD>8h would have poorer SRH, but no significant associations were found in this group or even in the very long sleeper group (>10h). Subjective reports of sleep time are often inaccurate. Self-rated SD modestly corresponds with more objective measurements of sleep involving polysomnography and/or actigraphy, and there is evidence that some individuals over-estimate their SD [34]. There is evidence in the literature showing that self-assessments of health are often mistaken [35] and may not be suitable for tracking changes in population health over time [36]. On the other hand, self-reported SD is well documented and a reliable measure. SD is an issue commonly used as a subjective sleep measure and is assessed by asking participants a simple question (e.g., “On average, how many hours of sleep do you have in a 24hour period?”) and categorizing the response into groups (≤5h, 6h, 7h, 8h, ≥9 or 10h) [37–39]. SRH is often measured by a single question (e.g., “In general, how would you say that your health is?”), and the respondents choose an option from a Likert scale that consists of five levels (poor, fair, good, very good or excellent). SRH provides an important and valid indicator of an individual׳s health status and associated health outcomes [40,41]. We cannot disregard the fact that self-reported or perceived variables/measures could be biased due to its subjectivity because some participants may have a different understanding of the categories of answers.