Dementia

The quality of included studies
The quality of the studies included in the survey was evaluated on
the basis of combined index, study design, scope of diagnostic
assessment, sample size, response proportion and overall quality.
Details can be found online in the web appendix to this report¹.
Meta-analysis of dementia prevalence
within GBD regions
There were sufficient studies of good quality to conduct meta-analyses
for 11 of the 21 GBD regions; Western Europe, North America,
Latin America (combining Andean, Central, Southern and Tropical
regions), Asia Pacific high-income, Australasia, East Asia, South-East
Asia and South Asia. For Latin America, we considered it pragmatic
and appropriate to pool studies from across the four GBD regions
to conduct a single continent-wide meta-analysis. Given that the
North American region comprised just Canada and the USA, and
that Canada was represented by a large and well-conducted survey
on a nationally representative sample (19), the national prevalence
figures for Canada were applied to Canada and the USA studies
were meta-analysed to generate estimates for that country.
Modelling the prevalence of dementia
Age-specific and age- and sex-specific meta-analysed dementia
prevalence estimates are described for each region in Table 2.1.
Prevalence increased exponentially with age in each region, doubling
with every 5.5 year increment in age in Asia Pacific, Latin
America and North America, with every 5.6 year increment in East
Asia, every 6.3 years in South Asia and Western Europe, and every
6.7 years in Australasia and South-East Asia. In all regions other
than Asia Pacific and North America, the predicted prevalence for
men was lower (by 19–29%) than that for women. There was a
tendency in all regions for the divergence in prevalence between
men and women to increase with increasing age; however, this was
statistically significant only for the Asia Pacific region. There was
statistically significant heterogeneity (variation in prevalence between
studies within regions) for all regions other than South-East.
Generation of prevalence estimates for
other GBD regions
Where it was impractical to conduct a meta-analysis due to insufficient
data, the default option was to apply relevant estimates from
the Delphi consensus of 2005, representing the best available
estimates of likely dementia prevalence in those regions (12). For a
full description of the strategies used, see online appendix¹.
Estimated prevalence of dementia
Estimated prevalence of dementia for all those aged 60 years and
over, age-standardized to the Western Europe population structure,
can be compared directly between the 21 GBD regions (Tables 2.1
and 2.2 and Figure 2.2). There is a four-fold variation, from 2.07%
(West sub-Saharan Africa) to 8.50% (Latin America). However, most
of the estimated age-standardized prevalence figures lie in a band
between 5% and 7%. The major source of variation is the very low
estimated prevalence for the four regions of sub-Saharan Africa.
Estimation of numbers of people with
dementia
Having applied the age-specific, or age- and sex-specific, prevalence
estimates to UN population projections, it was estimated that
35.6 million people worldwide were living with dementia in 2010
(Table 2.3). Western Europe is the GBD region with the highest
number of people with dementia (7.0 million), closely followed by
East Asia with 5.5 million, South Asia with 4.5 million and North
America with 4.4 million. The nine countries with the largest number
of people with dementia in 2010 (1 million or more) were China
(5.4 million), USA (3.9 million), India (3.7 million), Japan (2.5 million),
Germany (1.5 million), Russia (1.2 million), France (1.1 million), Italy
(1.1 million) and Brazil (1.0 million).
The total number of people with dementia is projected to almost
double every 20 years, to 65.7 million in 2030 and 115.4 million
in 2050. Much of the increase is attributable to increases in the
numbers of people with dementia in LMIC (Figure 2.3); in 2010,
57.7% of all people with dementia lived in LMIC, and this proportion
is expected to rise to 63.4% in 2030 and 70.5% in 2050. The projections
are driven mainly by population growth and demographic
ageing (Table 2.3). World regions fall into three broad groups. Highincome
countries start from a high base, but will experience only a
moderate proportionate increase – a 40% increase in Europe, 63%
in North America, 77% in the southern Latin American cone and
89% in the developed Asia Pacific countries. Other parts of Latin
America and North Africa and the Middle East start from a low base
but will experience a particularly rapid increase – 134–146% in the
rest of Latin America, and 125% in North Africa and the Middle East.
China, India and their neighbours in South Asia and Western Pacific
start from a high base and will also experience rapid growth – 107%
in South Asia and 117% in East Asia. Projected increases for sub-
Saharan Africa (70–94%) are modest and are consistent with limited
demographic ageing in view of persistently high child mortality and
the effects of the HIV epidemic.
1. http://www.who.int/mental_health/publications/dementia_report_2012
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