1. Can hearing aids prevent dementia?

2. Dementia
Symptoms: memory loss, mood changes, problems with communication and reasoning
Associated with age, but not necessarily ‘natural’ aging; caused by diseases of the brain (e.g. Alzheimers)

3. Dementia: high prevalence
Alzheimers UK website
1 in 3 people over 65 likely to experience dementia. Women more likely than men to experience dementia (longer life span)

4. Aging EU population
29.5% of EU population will be over 65 years by 2060
3x increased in very old (aged over 80 years)

5. Increasing numbers with dementia

6. Cost and prevention Profound impact on individual and family
Progressive, no cure
£23 billion pounds (£8 billion in social care)
Delay by 2 years  reduce prevalence by 13%
Delay by 5 years  reduce prevalence by 33%
Vickland, V., Morris, T., Draper, B., Low, L., & Brodaty, H. (2012). Modelling the impact of interventions to delay the onset of dementia in Australia. A report for Alzheimer’s Australia: Alzheimer's Australia.

7. Prevention?  Urgent need for research into prevention
Lower prevalence in younger generation
UK adults >65 years 8.3%
UK adults >65 years 6.5%
Matthews, F. E., Arthur, A., Linda E Barnes, L. E., Bond, J., Jagger, C., Robinson, L., et al. (2013). A two-decade comparison of prevalence of dementia in individuals aged 65 years and older from three geographical areas of England: results of the Cognitive Function and Ageing Study I and II. The Lancet, Published online July 16, 2013.
(low quality) evidence that
Diabetes, hyperlipidemia & smoking are associated with increased risk
Mediterranean-type diet, folic acid intake, low/moderate alcohol intake, cognitive activities and physical activity are associated with decreased risk
Daviglus, M. L., Bell, C. C., Berrettini, W., Bowen, P. E., Connolly, E. S., Cox, N. J., et al. (2010). National Institutes of Health State-of-the-Science Conference statement: preventing alzheimer disease and cognitive decline. Annals of internal medicine, 153(3),
 Urgent need for research into prevention
Medical Research Council Cognitive Function and Ageing Study; UK adults
Cambridgeshire, Newcastle, and Nottingham
MEDLINE and the Cochrane Database of Systematic Reviews from 1984 through October 27, 2009 for National Institutes of Health State-of-the-Science Conference

8. Could treating hearing loss reduce dementia?

9. Sensory losses associated with cognitive decline
Berlin aging study
687 people aged
Intelligence (14 tasks),
Vision and hearing acuity
Sensory function 94.7% age-related
& 12.6% age-independent variance
-sensory function and age-independent variance in intelligence
-sig greater in older age group (interpreted as being consistent with a common cause hypothesis; acceleration of changes in CNS affecting both cog and sensory performance with age)
-hearing and vision: 94.7% of age-related variance in cog, 12.6% of age-independent variance
 Association between sensory and cognitive functioning reflects brain aging; need to understand association
Lindenberger, U., & Baltes, P. B. (1994). Sensory functioning and intelligence in old age: a strong connection. Psychology and aging, 9(3), Baltes, P. B., & Lindenberger, U. (1997). Emergence of a powerful connection between sensory and cognitive functions across the adult life span: a new window to the study of cognitive aging? Psychology and aging, 12,

10. Hearing loss associated with increased risk of dementia
639 people aged 36 to 90. No dementia in ; BLSA
Followed up 11 years
Odds of dementia, adjusted for age, sex, race, ed level, diabetes, smoking, hi bp
Lin, F. R., Metter, E. J., O'Brien, R. J., Resnick, S. M., Zonderman, A. B., & Ferrucci, L. (2011). Hearing loss and incident dementia. Archives of Neurology, 68(2), 214.

11. Hearing loss and dementia
HL is associated with cognitive decline and an increased risk of dementia.
It is unknown whether these associations represent
i) a ‘common cause’ (such as vascular or neural changes that have independent effects on both cognition and sensory performance) and/or
ii) auditory deprivation (sensory deprivation impacting on cognition either directly via impoverished input or via knock-on effects of hearing loss on social isolation and depression)

12. Hearing aids prevent dementia?
If deprivation  cognitive decline and dementia
Remediate deprivation (e.g. by providing hearing aids)  slow cognitive decline and prevent dementia?

13. Impact of hearing aids on cognition
Study 1: UK Biobank
Associations between hearing aid use and cognition; cross-sectional analysis
Study 2: Epidemiology of hearing loss study
Comparison of cognitive outcomes in HA users vs non-users in a 20 year longitudinal data set

14. Study 1.
Model associations between hearing and cognition in the large UK Biobank data set.
Association of poor hearing with poor cognitive performance would be consistent with either the ‘common cause’ or deprivation hypotheses.
But if auditory deprivation contributes to cognitive decline, then one would expect that for equivalent levels of hearing loss, use of hearing aids would be associated with better cognitive performance.
Role of social isolation and/or depression

15. Participants: A subset of the UK Biobank resource (N= 164,770)
Hearing: Digit triplet test

16. Digit triplet test
(better-ear 50% speech recognition threshold)

17. Combine  cognitive function
Cognitive tests
If Truda’s mother’s brother is Tim’s sister’s father, what relation is Truda to Tim?
Select from:
- Aunt
- Sister
- Niece
- Cousin
- No relation
1. Fluid IQ
2. Reaction time
3. Memory
Combine  cognitive function

18. Hearing aid use: self report question "Do you use a hearing aid most of the time?”
Social isolation: self report question "Do you often feel lonely?" and number of social activities
Depression: "Over the past two weeks, how often have you felt down, depressed or hopeless?" and "Over the past two weeks, how often have you had little interest or pleasure in doing things?“

19. Structural equation modelling
Model and test causal relations
Hypothesis
variables and relations in a model
do the data fit the hypothetical model?

20. Structural equation modelling:
is the association between hearing loss and cognition may be mediated by hearing aid use, social isolation and/or depression?
Controlled: age, sex, general health and socioeconomic status

22. HEARING LOSS AND COGNITIVE DECLINE
Solid line = association
Dashed line = no association
SOCIAL ISOLATION
DEPRESSION
HEARING AID USE
COGNITION
Hearing aid use was associated with better cognition, and this was independent of social isolation and depression. This is consistent with the auditory deprivation model. However, statistical modelling of associations does not allow inferences about causation and there may be other explanations for the association. For example, cognitively more able people may tend to obtain and wear hearing aids.

23. Summary Study 1 HA use associated with better cognition
(effect of HA use, or smarter people use HA?)
If HA have a positive effect on cognition, it is unlikely to be via reduced social isolation/depression
Need longitudinal data

24. Study 2: Long-term outcome of hearing aid use
Among those with hearing loss, compare cognitive performance in hearing aid users versus non-users
Hypothesis: hearing aid users should have better cognition, lower incidence of cognitive impairment

25. Study 2. EHLS Longitudinal cohort Epidemiology of hearing loss (EHLS)
Subset of sample selected if they had hearing loss
Compare hearing aid users with non-users
Control for potential confounds (age, health, gender, hearing loss)

26. 5 years before baseline
No difference: gender, income, education level, ethnicity, general health
Poorer hearing
Baseline
Baseline + 5 years
Baseline + 11 years

27. Cognitive measures Cognitive performance Mini mental state
Trail making A&B
Digit-symbol substitution
Auditory verbal learning test
Verbal fluency test
Incident cognitive impairment
Doctor-diagnosed alzheimers, or
Fail Mini mental state exam
The AVLT (Schmidt, 1996) consists of two lists, A and B, of 15 unrelated words which are presented verbally. List A was presented three times in succession followed by the distracter list B. Participants were then asked to recall list A. The outcome was the number of words recalled correctly from list A, as a measure of recall.
The VFT (Strauss, Sherman, & Spreen, 2006) measures information retrieval from memory. Test-takers are required to orally name as many words as possible that begin with the letters F, A and S within 60 seconds. The outcome is the summed total number of words generated for each letter. The VFT Self-report questions

28. Baseline 5-years 11-years
Users (n=69)
Non-users (n=597) p
Users (n=50)
Non-users (n=440) P
Users (n=31)
Non-users (n=271)
MMSE score
26.7
(0.4)
26.5
(0.1)
.62
26.8
26.9
.77
25.9
(0.5)
(0.2)
.10
Trail-making test A score (sec) -
Trail-making test B score (sec)
65.0
(7.8)
57.5
(2.4)
.37
AVLT score (0-15)
147.5 (14.4)
148.3 (4.4)
.96
DSST score (0-93)
3.2
4.1
.09
VFT score
34.0
(2.1)
35.3
(0.7)
.59
Incidence of cognitive impairment
11.1%
15.5%
.49
1P-values are from multivariable logistic regression models (dichotomous outcomes; chi-square test of regression coefficient), and ANCOVA models (continuous outcomes; t-tests of least squares means). Models are adjusted for age, sex, and pure-tone average (.5,1,2,4 kHz, better ear) at the 5-year examination.

29. Summary
Study 1: hearing aid users had better cognitive performance. Supports possible impact of HA in improving cognition
Study 2. No differences in cognitive performance or incidence of impairment between hearing aid users and non-users. This is not supportive of a robust effect of hearing aid use as being protective against cognitive decline.

30. Why discrepancy?
Older US sample (but similar results in younger sample)
Different system for HA provision in US (but no difference in education level or income)
Lower power US sample size (but trend for worse performance by HA users)
Study 2 stronger design (more believable)

31. Hearing aids and living well
Dementia: cognitive impairment severe enough to impact on daily functional ability
Hearing loss may exacerbate disability
Hearing aids may decrease disability, thereby delaying the point at which ‘dementia’ may be diagnosed
Hearing aids may not prevent underlying brain pathology, but may improve quality of life and increase ‘healthy’ life span

32. Future
Intervention studies

33. Thanks
Manchester Kevin Munro, Richard Emsley Nottingham Mark Edmondson-Jones, Heather Fortnum, Abby McCormack Cincinnati Dave Moore Wisconsin Karen Cruickshanks, Mary Fischer, David Nondahl, Barbara Klein, Ron Klein