Mortality related to actigraphic long and short sleep

Abstract

Background: The folk belief that we should sleep 8 h seems to be incorrect. Numerous studies have shown that self-reported sleep longer than 7.5 h or shorter than 6.5 h predicts increased mortality risk. This study examined if prospectively-determined objective sleep duration, as estimated by wrist actigraphy, was associated with mortality risks.

Methods: From 1995-1999, women averaging 67.6 years of age provided one-week actigraphic recordings. Survival could be estimated from follow-up continuing until 2009 for 444 of the women, with an average of 10.5 years before censoring. Multivariate age-stratified Cox regression models were controlled for history of hypertension, diabetes, myocardial infarction, cancer, and major depression.

Results: Adjusted survival functions estimated 61% survival (54-69%, 95% C.I.) for those with sleep less than 300 min and 78% survival (73-85%, 95% C.I.) for those with actigraphic sleep longer than 390 min, as compared with survival of 90% (85-94%, 95% C.I.) for those with sleep of 300-390 min. Time-in-bed, sleep efficiency and the timing of melatonin metabolite excretion were also significant mortality risk factors.

Conclusion: This study confirms a U-shaped relationship between survival and actigraphically measured sleep durations, with the optimal objective sleep duration being shorter than the self-report optimums. People who sleep five or six hours may be reassured. Further studies are needed to identify any modifiable factors for this mortality and possible approaches to prevention.

Figure 1

Above: the distribution of the durations of actigraphic sleep for this sample enriched with those reporting long or short sleep. Below: the relative risk ratios (with 95% confidence bars) are shown for each actigraphic sleep duration, using 360–390 min. as the reference (black.) The minimum mortality was observed between 300–390 min. (5–6.5 hours), but statistical variability did not permit more precise localization of the minimum.

Figure 2

The estimated survival curves (adjusted for covariates in Model 4) are shown with the standard errors (SE). Those with actigraphic sleep durations shorter than 300 min. or longer than 390 min. had markedly reduced survival.