mortality rate of < 7h sleep with and without naps

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Francis Siefken

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Jan 8, 2013, 4:43:23 AM1/8/13
to polyphasic
Some info on the health risks of < 7 sleep with and without naps.


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To nap or not to nap: that is the question.
Mehra R, Patel SR.
Sleep. 2012 Jul 1;35(7):903-4. doi: 10.5665/Sleep.1946. No abstract available.
PMID:22754035
http://www.journalsleep.org/ViewAbstract.aspx?pid=28574

Sleep duration, nap habits, and mortality in older persons.
Cohen-Mansfield J, Perach R. Sleep. 2012 Jul 1; 35(7):1003-9. Epub 2012 Jul 1.
PMID:22754035[PubMed - indexed for MEDLINE] PMCID:PMC3368972[Available
on 2013/1/1]

Both short and long sleep duration have been shown to be associated
with adverse health outcomes and increased mortality, with a fairly
consistently reported U-shaped distribution and increased risks at
both ends of self-reported sleep time. The effect of napping on health
outcomes and mortality, however, is a bit more inconsistent and
ambiguous. In this issue of SLEEP, Cohen-Mansfield and colleagues1
studied night-time duration and nap habits in an Israeli cohort of
1,644 older individuals 75-94 years of age, the Cross-Sectional and
Longitudinal Aging Study (CALAS), for which 20-year follow-up
mortality data was available. The authors sought to examine the effect
of self-reported nighttime sleep duration on mortality and the effect
modification of daytime napping on the relationship of sleep duration
and mortality. The proposed hypothesis was to observe an increase in
mortality for long sleepers (> 9 hours per night) and short sleepers
(< 7 hours per night). The authors concluded that long sleep was
associated with an approximately 30% increased risk of mortality
compared to those obtaining 7-9 hours of sleep after adjusting for
confounders including subject characteristics and comorbid factors.
However, short sleep was not associated with an increase in mortality
in the fully adjusted model. In those who reported napping, a survival
benefit was noted in those obtaining < 7 hours of sleep, translating
into an approximate 20% improvement in mortality. In contrast, a
deleterious effect of napping was noted in those obtaining > 9 hours
of sleep, consistent with an approximate 40% increase in mortality
compared to those individuals obtaining “normal” duration sleep (i.e.,
7-9 hours). Furthermore, although the interaction of sleep duration
and napping was statistically significant in the unadjusted and
partially adjusted models, the interaction term was not significant in
the fully adjusted model taking into consideration confounding by
health status variables, including comorbidity, medications, and
depression.

The strengths of the study include the large sample size and
relatively novel examination of the interplay of napping in sleep
duration and mortality. Study limitations include the self-report and
subjective nature of obtaining the sleep duration and nap habit
measures, restricted generalizability, and the suboptimal fidelity of
these measures assessed at one point in time as reflective of baseline
sleep characteristics predicting future mortality over the 20-year
follow-up period.

This study complements contemporary studies in regard to potential
mechanisms affecting population health. In this cohort with mean age
of 83 years, long but not short sleep duration was associated with
increased mortality. Existing data, including those derived from an
older cohort, suggest that long sleep duration may be associated with
up-regulation of pro-inflammatory pathways involving increases in
hs-C-reactive protein, interleukin-6, and fibrinogen.2,3 These data
suggest a role for increased systemic inflammation in long-sleep
duration pathogenesis, including the somnogenic effect of cytokines,
which may exert detriment in a bi-directional manner relative to long
sleep duration to perpetuate the process of increasing adverse
outcomes and mortality. Although the long sleep duration-mortality
relationship in the current study was noted independent of
comorbidities including depression, the possibility of residual
confounding cannot be excluded, particularly as many of the
comorbidities may increase risk of fatigue, sleepiness, and a
bed-bound state and potential confounding from sleep disorders.

The absence of short sleep duration as a mortality risk in this cohort
is somewhat unusual, particularly in the face of a wealth of data that
has amassed implicating short sleep duration as a contributor to
increased mortality. The current findings could be a result of
measurement error of sleep duration given it is well recognized that
self-reported sleep duration is often an overestimate of true sleep
duration. The survivorship bias could also exist, such that those
individuals who have survived may be more immune to the negative
sequelae of short sleep duration, or resistant because of a background
effects (e.g., genetic susceptibilities). Furthermore, the differences
in the relationship of short versus long sleep and mortality may be
due to the notion that sleep duration represents a surrogate for
social interactions, which may be the true causal factor.

The highlight feature in this study by Cohen-Mansfield et al.,1
however, is the observed effect of napping on the relationship of
sleep duration and mortality in the stratification analysis. Why would
short nighttime sleepers (< 7 hours) experience a reduced mortality
(i.e., a protective effect), in those with self-reported napping? One
possibility is that theoretically the total sleep time achieved over a
24-hour period may come closer to the optimal 8 hours recommended for
the average adult in those who have short sleep along with the
additional sleep time supplemented by napping. However, following this
logic, it is still unclear why this sleep pattern would convey a
benefit of reduced mortality compared to those individuals who report
“normal” sleep duration of 7-8 hours. A potential basis could be a
protective effect of siesta on mortality,4 which has been described
with relative inconsistency in the literature. On the other side of
the sleep duration spectrum, however, the opposite finding was noted
with long sleep duration such that an increase in mortality was
observed. Recent data from an older cohort of men also support an
association between long sleep duration and napping.5 Conceivably, in
those with self-reported napping, a further increase in sleep in those
designated as long sleepers may result in an augmented increase in
mortality due to enhancement of a pro-inflammatory state, although
existing data do not specifically describe graded relationships of
increasing sleep time with increasing levels of systemic inflammation.
Notably, the mitigation of the napping statistical interaction in the
fully adjusted model likely reflects either an underpowered sample
size or true confounding by poorer health. Although the effect
modification by napping is intriguing, the possibility that this
finding represents a false positive should be considered. Aspects that
refute this include the fact that the magnitude of the difference is
clinically important, the subgroup analysis was one of a small number
tested, and there appears to be indirect evidence supporting the
difference.

The current work highlights the importance of examining the
intersection of sleep duration, sleep-wake patterning and wake time
napping and mortality and also uncovers complexities in data
interpretation when investigating the relationships of sleep duration
and day/night sleep-wake patterns on outcomes. Future epidemiologic
studies should be conducted to examine the relationships of sleep
duration, napping, and health outcomes with additional attention to
circadian rhythm influences to assess reproducibility of the current
findings and also to unveil potential mediating pathophysiologic
pathways.


Sleep duration, nap habits, and mortality in older persons.
Cohen-Mansfield J, Perach R.
Sleep. 2012 Jul 1;35(7):1003-9. doi: 10.5665/sleep.1970.
PMID:22754047

Abstract

OBJECTIVE: To examine the effect of nighttime sleep duration on
mortality and the effect modification of daytime napping on the
relationship between nighttime sleep duration and mortality in older
persons.

DESIGN: Prospective survey with 20-yr mortality follow-up.

SETTING: The Cross-Sectional and Longitudinal Aging Study, a
multidimensional assessment of a stratified random sample of the older
Jewish population in Israel conducted between 1989-1992.

PARTICIPANTS: There were 1,166 self-respondent, community-dwelling
participants age 75-94 yr (mean, 83.40, standard deviation, 5.30).

MEASUREMENTS: Nighttime sleep duration, napping, functioning
(activities of daily living, instrumental activities of daily living,
Orientation Memory Concentration Test), health, and mortality.

RESULTS: Duration of nighttime sleep of more than 9 hr was
significantly related to increased mortality in comparison with
sleeping 7-9 hr (hazard ratio [HR] = 1.31, P < 0.01) after adjusting
for demographic, health, and function variables, whereas for short
nighttime sleep of fewer than 7 hr mortality did not differ from that
of 7-9 hr of sleep. For those who nap, sleeping more than 9 hr per
night significantly increased mortality risk (HR = 1.385, P < 0.05)
and shorter nighttime sleep reduced mortality significantly in the
unadjusted model (HR = 0.71, P < 0.001) but only approached
significance in the fully adjusted model (HR = 0.82, P = 0.054). For
those who do not or sometimes nap, a short amount of sleep appears to
be harmful up to age 84 yr and may be protective thereafter (HR =
1.51, confidence interval [CI] = 1.13-2.02, P < 0.01; HR = 0.76, CI =
0.49-1.17, in the fully adjusted model, respectively).

CONCLUSIONS: The findings are novel in demonstrating the protective
effect of short nighttime sleep duration in individuals who take daily
naps and suggest that the examination of the effect of sleep needs to
take into account sleep duration per 24 hr, rather than daytime
napping or nighttime sleep per se.


Nighttime sleep, Chinese afternoon nap, and mortality in the elderly.
Lan TY, Lan TH, Wen CP, Lin YH, Chuang YL.
Sleep. 2007 Sep;30(9):1105-10.
PMID:17910382
Free PMC Article
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1978410/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1978410/pdf/aasm.30.9.1105.pdf

Abstract

STUDY OBJECTIVES: Although many epidemiologic studies have shown that
both short and long nighttime sleep durations are associated with
increased mortality in the general population, limited data have been
reported for older persons, especially those taking afternoon nap.
Data from a prospective cohort study of the elderly in Taiwan were
used to examine the relationship among nighttime sleep, Chinese
afternoon nap, and mortality.

DESIGN: Prospective cohort study.

SETTING: General population.

PARTICIPANTS: A nationally representative sample of 3079 Taiwanese
community residents aged 64 and over was studied, using reported sleep
related information collected in 1993 and subsequent 10-year mortality
data.

INTERVENTIONS: None.

MEASUREMENTS AND RESULTS: Cox proportional hazards models, separated
by sex, were computed to estimate mortality hazard ratios in relation
to nighttime sleep duration and afternoon nap duration, adjusting for
potential confounders. Compared to older adults sleeping 7-7.9 hours
at night, those with longer sleeping time (> or = 10 hours in males
and > or = 8 hours in females) had a significantly higher risk of
total mortality. Afternoon nap alone was not associated with total
mortality. When nighttime sleep duration and afternoon nap duration
were considered together by adding the interaction term in the model
or stratifying sleep hours and nap duration, the effect of afternoon
nap on mortality risk remained insignificant.

CONCLUSIONS: Longer nighttime sleep duration increases mortality risk
in older adults. Chinese afternoon nap is not an independent predictor
of mortality. There is no significant benefit or harm of practicing
afternoon nap in addition to the regular night sleep on elderly
mortality.

John Litborn

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Jan 8, 2013, 3:36:23 PM1/8/13
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Wow, that was a long and hard read! It isn't terribly related to what
most people (want to) do on this mailing list though. Pretty much the
only tl;dr you can give is that it's good to take a nap during the
afternoon, and it's bad to sleep a long time. Thanks for the articles
anyway!
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