Sleep disorders Abstract Associations of sleep characteristics with mild cognitive impairment MCI have been examined in cross-sectional, but rarely in longitudinal studies. MCI was assessed with extensive cognitive tests. Sleep questionnaires including PSQI Pittsburgh Sleep Quality Index were used to assess sleep quality, sleep disturbances, time asleep, and time in bed. Relative risks RR of developing MCI when exposed to sleep characteristics were assessed in regression models adjusted for sociodemographic and cardiovascular risk factors. In this longitudinal study with older participants, MCI risk was increased in persons with poor sleep quality, difficulties initiating sleep, and short time in bed.
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Sleep disorders Abstract Associations of sleep characteristics with mild cognitive impairment MCI have been examined in cross-sectional, but rarely in longitudinal studies.
MCI was assessed with extensive cognitive tests. Sleep questionnaires including PSQI Pittsburgh Sleep Quality Index were used to assess sleep quality, sleep disturbances, time asleep, and time in bed. Relative risks RR of developing MCI when exposed to sleep characteristics were assessed in regression models adjusted for sociodemographic and cardiovascular risk factors. In this longitudinal study with older participants, MCI risk was increased in persons with poor sleep quality, difficulties initiating sleep, and short time in bed.
In an estimated By it is expected that this number triples to Because no effective causal medical therapies are available for dementia, primary prevention of dementia and of its early precursors is the most promising option currently available to cap the rising prevalence 4 , 5. Therefore, identification of modifiable risk factors for incident MCI is important, and poor sleep is considered a potential risk factor for cognitive decline and disease progression 6 , 7 , 8 , 9 , 10 , 11 , 12 , Sleep characteristics were suggested as modifiable risk factors for cognitive decline, for example by influencing hippocampal volume 14 , Two up-to-date reviews on this relationship indicate an association between cognitive decline and sleep problems, such as poor sleep quality, short or long sleep duration, and sleep disturbances 12 , However, both reviews concluded that there is still a need for long term prospective studies to ensure that sleep problems precede cognitive decline 12 , Two recently published cohort studies on sleep characteristics and dementia were not included in these reviews 17 , Both suggest that self-reported long sleep duration as well as self-reported sleep disturbances increase the risk of dementia.
Additionally, Jackowska and Cadar 19 found an association between decreased cognitive function and self-reported long and short sleep duration in their prospective cohort study. However, there is still a knowledge gap for longitudinal studies on sleep characteristics and mild cognitive impairment.
To this purpose, we examined the relationship between multiple sleep exposures overall sleep quality; difficulties maintaining or initiating sleep, early-morning awakening; time in bed, time asleep i. The study rationale and design have been described in detail elsewhere 20 , In short, the cohort comprises a total of 4, participants The baseline visits t0 were performed between and The median follow-up time was 5.
Data assessment at baseline and at follow-up visits included a self-administered questionnaire, face-to-face interviews, and a physical examination including among others anthropometric measurements and comprehensive laboratory tests.
The study was performed in accordance with the approved guidelines and regulations. All participants gave their written informed consent. In the HNR Study, cognitive tests were performed at the second t1 and the third visit t2 at the study centre.
Participants were included into the present study if data were available for all variables of interest for the complete case analysis Fig. Figure 1 Flow-chart of persons entering the complete case analysis dataset. The first five subtests had already been performed at t1. For a detailed description of tests 1 to 5 see Wege et al. Except for the clock-drawing test, the age- and education-adjusted test scores were scaled to have a mean of 10 and a SD of 3 Within each domain attention, executive function, verbal memory and visuoconstruction , newly scaled scores of the tests were added.
To account for the differing numbers of tests in each domain, domain scores were then scaled to have a mean of 10 and a SD of 3 Table 1 Description of cognitive domains.
Full size table Definition of mild cognitive impairment The MCI diagnosis at t2 was based on the following published MCI criteria 29 , 30 : 1 cognitive impairment in at least one of the above reported four domains; 2 subjective cognitive decline over the past two years; 3 generally intact activities of daily living; 4 no dementia diagnosis Because cognitive assessment at t1 consisted of only five subtests, we were unable to build cognitive domain scores at this time-point.
Assessment of sleep characteristics Sleep variables were assessed in a computer-assisted interview. The questionnaire consists of seven sub-scores that are described in detail elsewhere Nocturnal sleep duration We used the two following variables to assess self-reported nocturnal sleep duration: 1.
This may be different than the number of hours you spend in bed. The question about nap frequency had the following choices: never, less than once a week, one to four times per week, five to six times per week, and daily. Mean duration of daytime napping was calculated as reported duration of daytime napping multiplied by its relative frequency. Total sleep duration was calculated as the sum of time in bed during the night plus duration of daytime napping.
Sleep duration was categorised because of the hypothesized non-linear dependency and the tendency of participants to answer in half-hour intervals. Covariates As part of the first follow-up visit of the HNR Study at t1, information about medical and family history, cardiovascular risk factors, lifestyle and various sociodemographic factors were assessed in a computer assisted interview 20 , The variables used for model adjustment were selected based on a directed acyclic graph DAG based on current literature on the topic.
Further details on the covariate assessment have been described elsewhere 21 , We did not categorise the continuous variables used in the adjustment set. The outcome variable was incident MCI, exposure variables were global sleep quality assessed by the PSQI score, sleep disturbances, time asleep, time in bed, and total sleep duration.
For each exposure of interest, we calculated three models: first, a crude model cf. A table detailing patterns of missing in all variables used in the imputation can be found in the supplementary material cf. The overall fraction of missing data was 2. This ranged from no missing data e.
All statistical analysis was performed using SAS 9. Further, we wished to avoid publication bias by preferential reporting of statistically significant results. Instead, we judged our estimates by their precision and validity. Additional analyses We used changes of sleep duration between T1 and T0 as a further exposure of interest. Additionally, we stratified our cohort into three age groups 45 to 54, 55 to 64 and 65 to 74 years to look for effect modification by age.
Furthermore, we stratified our cohort by APOE carrier status to investigate effect modification. For these additional analyses, we used the same modelling procedures and adjustment sets as described above. These participants had more difficulties maintaining sleep, more difficulties initiating sleep, and more often reported early-morning awakening. Alcohol consumption and depression scores were highest and physical activity the lowest in persons with 5 or less hours of nocturnal sleep duration.
Table 2 Baseline characteristics stratified by nocturnal sleep duration: the Heinz Nixdorf Recall Study. Table 3 Adjusted relative risks for the association between sleep quality, and sleep disturbances, respectively, and the incidence of mild cognitive impairment at t2: the Heinz Nixdorf Recall Study.
Sleep duration We observed a U-shaped association between time in bed during the night and incident MCI as well as between total sleep duration time in bed during the night plus daytime napping and incident MCI cf.
Table 4 Adjusted relative risks for the association between subjective sleep duration and the incidence of mild cognitive impairment at t2: the Heinz Nixdorf Recall Study. Estimates of relative risk were obtained from log-linear model with a Poisson working likelihood and robust standard errors. Missing values were imputed. Sleep duration was assesed as a categorical variable.
Dots are the means of their respective category. Full size image Multiple imputations The use of multiple imputations MI yielded different results compared to the complete case CC analysis. MI resulted in more precise estimations. Point estimates for some of the relative risks diverged. Additional analyses We calculated change of sleep duration between T1 and T0 from sleep duration measured at T1 and T0. Persons who reported shorter nocturnal or total sleep duration at T1 compared to T0 had a higher risk of MCI: a decrease of sleep duration of at least one hour was associated with a 1.
In age-stratified analyses, the U-shaped association between time in bed and total sleep duration and incident MCI was strongly pronounced in the two older age groups 55 to 64, 65 to 74 years , but not in the youngest.
However, in the youngest group 45 to 54 years , an increased MCI risk was not observed for any sleep duration parameter, but more strongly for sleep quality parameters cf. In the analysis stratified by the APOE carrier status, we observed a stronger influence of difficulties maintaining sleep, early morning awakening and sleep quality in non-carriers, e.
Full size table Discussion In our prospective cohort study, a higher risk of MCI was observed in persons with self-reported poor overall sleep quality, in persons who reported short time in bed, and persons with a strong decrease of sleep duration before baseline. Moreover, persons who reported difficulties initiating sleep almost every night had a higher risk of incident MCI five years later. For persons reporting difficulties maintaining sleep or early morning awakening, the risk for MCI was not increased.
Results for sleep duration depended on whether time awake in bed was included or excluded in the calculation for sleep duration: For persons with short or long time asleep, there was no evidence of higher MCI risk.
This in line with the study by Blackwell et al. Persons with a strong decrease of sleep duration at first follow-up compared to baseline had a higher risk of MCI. However, whether change of sleep duration itself or short sleep duration is the primary cause of higher MCI risk cannot be answered by our study. Our results based on longitudinal HNR Study data are in line with earlier cross-sectional analyses of the same cohort. Dlugaj et al. Regarding sleep disturbances identical item , results from the earlier cross-sectional study could be replicated in the present longitudinal study.
Similar results have also been reported in two other prospective studies on sleep patterns and cognitive decline. Potvin et al. In another prospective analysis, Keage et al. Regarding long sleep duration, several studies showed long sleep to be associated with impaired cognitive performance 13 , 40 , 41 , For instance, Ramos et al.
However, most studies also used self-reported sleep duration and did not explicitly exclude time awake in bed from their sleep duration calculation.
In concordance, a specific pathway between long sleep duration and cognitive decline is not known. Long sleep duration is associated with cerebrovascular disease 43 , 44 which is a contributor to cognitive impairment and cognitive decline 45 , Persons with cardiovascular disease have more often problems in maintaining sleep 47 , When hours awake in bed are not explicitly excluded, those persons might tend to recall longer sleep durations without subtracting time awake in bed.
This might be an explanation for the vanished U-shaped association in our cohort. However, this finding has to be confirmed in studies with objective sleep measurements and incident MCI.
Heinz Nixdorf Recall MehrGenerationenStudie
The Heinz Nixdorf Recall Study The true relevance of coronary calcifications -- and more important discoveries still to come for decades Initiated in , the Heinz Nixdorf Recall Study involved 4, European participants. The results proved, for the first time, the connection between coronary calcifications and the risk of heart attack, according to scientists at the University Hospital in Essen. The finding by no means exhausted the potential inherent in the surveys. Subsidised until , researchers are examining coronary calcifications in detail as well as exploring other issues. RE: For specialists the results mean a change in thinking is needed, which, in itself, necessitates a learning process. Suddenly, risk determination requires not only a check on cholesterol levels and blood pressure, but also an additional CT scan to assess the calcium score, if the preliminary examination shows a medium level risk of heart attack.
[The Heinz Nixdorf Recall study].