Sleep disturbances and cognitive function in the English Longitudinal Study of Ageing (ELSA) Michelle A. Miller ESRC Oxford Research Methods Festival St.

Sleep disturbances and cognitive function Sleep disturbances and cognitive function in the English Longitudinal Study of Ageing in the English Longitudinal Study of Ageing

(ELSA)(ELSA)

Michelle A. Miller

ESRC Oxford Research Methods FestivalSt. Catherine’s College, Oxford,

8-10°July 2014

University of Warwick, ‘Sleep, Health & Society Programme’ Warwick Medical School, Coventry, UK

OverviewOverview• Background / setting

• Study aim

• Methodological considerations with reference to SDAI

• Results

• Limitations

• Conclusions

Background settingBackground setting• Sleep disturbances are important predictors of ill-health • Cognitive decline common in older age (Bozoki et al, 2013)• 1 in 9 develop Alzheimer’s by age 75yrs (McDowell, 2001)• Dementia affects ~800,000 people in the UK

• Is Sleep a risk factor?• Explore using SDAI• Utilise ELSA

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Sleep and cognition in an ageing population. Sleep and cognition in an ageing population. The English Longitudinal Study of Ageing (ELSA)The English Longitudinal Study of Ageing (ELSA)

Aims:

To assess the evidence for associations between sleep quantity and quality and amnestic and non-amnestic cognitive function.

Hypotheses:•Poor quality and short/long sleepers will have poorer cognitive function than optimal sleepers

•Amnestic and non-amnestic functions may be affected differently by poor sleep.

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Methodological considerations for secondary Methodological considerations for secondary data analysisdata analysis

• Population• Representative • Size and Power• Confounders • Exposure and outcome measures • Follow-up data • Study design

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The English Longitudinal Study of Ageing (ELSA)The English Longitudinal Study of Ageing (ELSA)

Cohort Panel study:• Population

– Cohort of men and women aged ≥50 years– Started in 2002, follow up every 2 years– Computer-assisted personal interview, self-completion

questionnaire, nurse visitRepresentative

– UK representative sample– ELSA is harmonized with ageing studies in other countries

to facilitate international comparisons.

A Steptoe, et al.Int J Epidemiol. 2013 Dec;42(6):1640-8..

Methodological considerations for secondary Methodological considerations for secondary data analysisdata analysis

• Population• Representative • Size and Power• Confounders • Exposure and outcome measures • Follow-up data • Study design

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The English Longitudinal Study of Ageing (ELSA)The English Longitudinal Study of Ageing (ELSA)

• Size and power– Original sample N = 11,391

• Confounders

– Economic, social, psychological, cognitive, health, biological and, genetic data

– Linked to financial and health registry data

The data set is openly available to researchers and analysts (http://www.esds.ac.uk/longitudinal/access/elsa/l5050.asp).

A Steptoe, et al.Int J Epidemiol. 2013 Dec;42(6):1640-8..

Methodological considerations for secondary Methodological considerations for secondary data analysisdata analysis

• Population• Representative • Size and Power• Confounders • Exposure and outcome measures • Follow-up data • Study design

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Exposure and OutcomeExposure and Outcome

10Analysis of covariance (ANCOVA)

Is the exposure robust and valid? Is the exposure robust and valid?

Limitations Advantages

Sleep QuantityHow many hours sleep do you get on an average week night?

Questionnaire based (self-reported sleep)

• Large number of responders

• Free response(continuous or categorical data)

Sleep QualityHow frequently do you:i) Have difficulty falling asleepii) Wake up several times in the nightiii) Wake up feeling tired and worn out

1 = Not in past month; 2 = Less than once a week;

3 = Once or twice a week; 4 = Three or more per week

iv) Self-rated sleep quality1 = Very good; 2 = Good; 3 = Fairly bad; 4 = Very bad

Questionnaire based (Self-reported)

• Multiple components of Sleep quality recorded

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Is the outcome robust and valid? Is the outcome robust and valid?

Amnestic Non-amnestic• Orientation in time

- Date questions. Can you tell me“todays date”

• Word learning and recall - 10 words; immediate and delayed recall

• Prospective memory- ‘Remembering to remember’. Instructions for later task e.g. to write initials on paper.

• Word finding (verbal fluency)- Naming animals

Eg. Name as many different animals as you can in one minute.

• Letter cancellation- Attention, mental speed & visual scanning

• Numeracy- Mental arithmetic

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Methodological considerations for secondary Methodological considerations for secondary data analysisdata analysis

• Population• Representative • Size and Power• Confounders • Exposure and outcome measures • Follow-up data • Study design

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English Longitudinal Study of Ageing (ELSA)

Prospective population panel study of British men and women, aged 50+ years

Wave 1 (2002/3)N = 12,099•Main interview (inc. cognition)

Wave 2 (2004/5)N = 9,432•Main interview (inc. cognition)•Nurse visit

Wave 3 (2006/7)N = 9,771•Main interview (inc. cognition)

Wave 4 (2008/9)N = 11,050•Main interview (inc. cognition)•Nurse visit•Sleep data

Wave 5 (2010/11)N = 10,275 (approx)•Main interview (inc. cognition)

ESRC SDAI Phase 1 “Sleep disturbances and cognition in ELSA”

ESRC SDAI Phase 2 Prospective analysis(application pending)

ResultsResults

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  YOUNGER (50-64 years) OLDER (65+ years)

< 6hr 6 - 8hr > 8hr p < 6hr 6 - 8hr > 8hr p2

N [%]

646[13.9]

3778[81.1]

236[5.1]

  607[14.7]

3136[76.0]

386[9.3]

Sex (% male)

37.3 46.2 38.6 <0.001 37.4 47.5 45.3 <0.001

Age (years)

57.9 (3.8) 57.9 (3.8) 58.3 (4.2) =0.252 73.9 (6.1) 73.2 (6.1) 74.5 (6.5) <0.001

Amn(T score)

48.4 (6.3) 50.4 (6.2) 48.6 (6.9) <0.001 49.4 (6.6) 50.4 (6.7) 47.5 (8.4) <0.001

Non-amn (T score)

48.8 (5.5) 50.3 (5.4) 48.4 (5.8) <0.001 49.2 (5.7) 50.4 (6.0) 48.3 (6.2) <0.001

Results expressed as mean (SD) or %.]ANOVA for continuous data, chi-square for categorical data (where p value represents differences between all categories)Miller et al., PLOS ONE 2014 (In press)

Significant interactions were detected between sleep disturbances (quantity and quality) and age. Responders were separated into younger (50-64 years; n= 4,660) and older (65+ years; n=

4,129).

Fully adjusted amnestic and non-amnestic function T-scores by sleep quantity and quality

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Sleep QUANTITY (Left panel): •Younger Group: amnestic (p=0.003); non-amnestic (p=0.010)•Older Group: amnestic (p=<0.001); non-amnestic (p<0.001)

*Adjusted for: age, sex sleep*age, education, employment grade, depression, physical activity, smoking, general health.Miller et al., PLOS ONE 2014 (In press)

Sleep QUALITY (Right panel): •Younger group: No significant associations •Older group: amnestic (p=<0.001); non-amnestic (p<0.001)

Cognitive function scores by sleep categories adjusted for sleep quality.

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LEFT PANEL: Adjusted mean amnestic T Score

Analysis of covariance (ANCOVA) for sleep quantity and/or sleep quality, for amnestic or non-amnestic scores, and in both younger (50-64yrs) and older (65-89yrs) age groups (PLOS ONE in press.

RIGHT PANEL: Adjusted mean non-amnestic T Score

LimitationsLimitations• Cross-sectional - reverse causality • Need for prospective studies• Self-reported sleep• Questionnaires have been validated against PSG (but not in

older population)

• Large, representative older cohort• Wealth of data on cognition and confounders

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StrengthsStrengths

ConclusionsConclusions

• Different associations between sleep and cognition in younger and older adults– Sleep quality only associated with cognition in older adults

• Similar associations for amnestic and non-amnestic function

• Prospective studies to reveal relationship between sleep and changes in cognition with ageing

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AcknowledgmentsAcknowledgments

Wingate

Hayley Wright, Chen Ji, Francesco P. Cappuccio

We thank the following organizations for supporting our Programme and, specifically the ESRC for this project (ES/K002910/1).

Sleep quantity and sleep quality.

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Mean sleep quality score for each sleep quantity category (upper panel, S1A-S1B), and mean sleep quantity (hours) for each sleep quality tertile (lower panel, S1C-S1D), in younger and older age groups. All unadjusted ANOVAs p < 0.001; see figures for p values for multiple comparisons (Bonferroni-corrected).