Dementia 2nd ed - Alzheimer's disease and ethnicities

The incidence of AD could be different in other countries or
in other ethnic groups. This could be because of different environmental
exposures throughout life, including dietary patterns, or because of different
gene frequencies in the contrasted populations. A meta-analysis of
incidence studies found that East Asian countries had a lower incidence of
dementia, and a lower incidence of AD at younger ages, than countries with
predominantly Caucasian populations. Japanese studies have often
found that vascular dementia is more prominent than AD. However,
Japanese-Americans, who have oriental ancestry but have adopted American
culture, are more like Caucasians in having a preponderance of AD
. Recent studies in Japan indicate that the Japanese may have gradually
moved to the Caucasian pattern of dementia. although Hatada et al
attribute the change largely to different ascertainment practices in recent
years. Overall, the findings suggest that there may be some important
genetic or environmental factors which produce a different pattern of
dementing diseases. Possible factors are the higher intake of salt in the
Japanese diet (predisposing them to high blood pressure and vascular
dementia) and the lower frequency of the ApoE e4 allele in the Japanese
(lowering their risk of AD).
Another interesting study has compared the prevalence and incidence of
dementia in Black Americans and Nigerians [72,73]. Both groups are of West
African ancestry, but they have very different lifestyles. The Nigerians have
been found to have a lower prevalence and incidence of AD and of dementia
generally.
The Cree Indians in Canada have also been found to have a lower prevalence
of AD than White Canadians, but they did not differ in the prevalence
of all dementias because they had more alcoholic dementia [74]. It is important
to note, however, that the Cree study has reported a lower prevalence of
AD, not a lower incidence. The difference in prevalence could be due to a
lower incidence in the Cree or to shorter survival after developing AD.

- dementia 2nd ed