Prevalence of dementia in the older Japanese-Brazilian population

Authors


address: Tatsuo Yamada, Department of Internal Medicine and Health Care, Fukuoka University, School of Medicine, 7-45-1, Nanakuma, Johnan-ku, Fukuoka 814-0180, Japan. Email: tyamada@fukuoka-u.ac.jp

Abstract

Abstract The prevalence of dementing disorders in Campo Grande of a community of Japanese-Brazilians who immigrated from Okinawa was studied. Previous reports showed that the dietary pattern in Japanese immigrants in Brazil, which characterized by a low fish and large meat intake, is possibly responsible for increased risk of cardiovascular diseases compared with Japanese in Okinawa. A total of 157 persons over 70-year-old were examined, and 19 cases were diagnosed as having dementia. The prevalence (cases/100 aged 70-year-older) was 12.1 for all types of dementia, 5.7 for Alzheimer's disease (AD), 0.6 for vascular dementia (VD), 4.5 for mixed dementia (AD/VD) and 1.3 for other types of dementia. There was no case of dementia with Lewy bodies or frontotemporal lobar degeneration. These results are similar to many previous studies in Western countries and some recent surveys in Japan, and clearly show that more AD than VD appears even in the Japanese-Brazilian population. The higher prevalence rate of dementia in Japanese-Brazilians compared with several studies in Japan may indicate the importance of dietary factors rather than genetic factors.

INTRODUCTION

Several surveys have indicated that 5–17% of persons over 70 years have a dementing illness.1,2 Different frequencies of two major subtypes of dementia, Alzheimer's disease (AD) and vascular dementia (VD), had been reported in various nationalities. Alzheimer's disease is the major subtype in many Western countries, while VD has often been reported to be dominant in Japan.3–8 However, some recent epidemiological studies in Japan found the same tendency towards more AD than VD as in Western countries.9–11

Although the cause of AD is still unknown, genetic factors seem to play an important role in its etiology. Among these, apoE ɛ4 allele is now considered to be the most common risk factor for sporadic late-onset AD. In addition, some other environmental factors have been thought to contribute to AD pathology, including early-life environment12 and dietary factors.13

Japan has the longest life expectancy in the world. Among the 47 prefectures in Japan, Okinawa is the top-ranking region in average life expectancy. Before the Second World War, a large number of Japanese emigrated to North and South America. Since 1908, 260 000 Japanese people have moved from Japan to Brazil. Studies comparing the population in Okinawa with emigrants from Okinawa in the field of cardiovascular disease have found evidence of several differences in ischemic heart disease risk factors, and studies on mortality of Japanese immigrants in Brazil have indicated a shift in cause of death towards that of non-Japanese Brazilians.14 Further studies on Japanese-Brazilians in Campo Grande, originally from Okinawa, revealed that they showed double the prevalence of ST-T changes in electrocardiogram and of hypertension, than did the Japanese in Okinawa.15 The dietary patterns of Japanese immigrants in Brazil, characterized by a low fish and large meat intake, have been suspected to be closely linked to the higher rate of cardiovascular diseases, indicating the importance of dietary factors rather than of genetic factors.16

In the present study, we investigated the prevalence of dementing disorders in the Japanese population in Campo Grande, originally from Okinawa, and compared the data with studies on Japanese-American and Japanese communities, including Okinawa. We found a relatively higher prevalence rate of dementia in Campo Grande than reported in other studies.

MATERIALS AND METHODS

The epidemiological study was done in 2000 for the Japanese-Brazilian population in Campo Grande in Brazil. To be included in the study, subjects were required to be living and to legally reside in the town on 1 August 2000 (prevalence day). The population of Campo Grande in 2000 was approximately 600 000. The number of elderly people over 70-year-old, immigrated from Okinawa, was about 200. Among them, we examined the 157 subjects. The participants were recruited randomly by mail from ‘Okinawa Kenjinnkai’ (the association for immigrants from Okinawa). In this Japanese community, almost all the disabled patients with chronic diseases had been managed in their house under the control of family doctors.

In phase 1 study, a brief screening examination for all the subjects over 70 years old was done by a nurse or a neurologist. The screening examination included an interview of the subjects and their families which surveyed activities of daily living, psychological and medical symptoms, the medical history of the subject and the Mini-Mental State Examination (MMSE). Based on the results of previous studies,17 a cutoff point of 23/24 in the MMSE was chosen. In phase 2, all cases who showed questionable or definite cognitive impairment in phase 1 were examined by a neurologist. An assessment was made of the medical histories from the family and clinical examinations were done. Brain computed tomographies (CT) obtained in a clinic were also used for diagnosis in these cases. The diagnosis of dementia was defined using DSM-III-R criteria.18 Patients who satisfied the criteria recommended by the National Institute of Neurological and Communication Disorders and Stroke-Alzheimer's disease and Related Disorders Association (NINCDS-ADRDA)19 were diagnosed as having probable AD. Patients who satisfied the criteria recommended by the National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neuroscience (NINDS-AIREN)20 were diagnosed as having probable VD. Patients who fulfilled the criteria by the consensus guideline for the clinical diagnosis of probable and possible dementia with Lewy bodies (DLB)21 were diagnosed as having probable DLB. Patients who fulfilled the criteria of frontotemporal lobar degeneration (FTLD)22 were diagnosed as having FTLD. We excluded cases of cognitive decline secondary to depression and other psychiatric diseases through a psychiatric interview and medical history. For 10 subjects who could not be examined directly, we collected information from family members, the public nurse, and physicians in the town. Prevalence was calculated for dementia of all types and for specific dementing disorders.

RESULTS

The study population included 157 subjects aged 70–100 years of age residing in Campo Grande on prevalence day. The phase 1 study, performed over about 1 month (August 2000), identified 28 cases as having questionable or definite cognitive impairment. The subjects who could not be examined directly were diagnosed as non-demented. The number of subjects who were diagnosed as having dementia in the phase 2 study was 19, yielding a prevalence for all dementias of 12.1 cases/100. One of the other nine cases who was picked-up in phase 1 study and diagnosed as non-demented in phase 2 study had neurosis and others were diagnosed as age-related cognitive decline. The age-specific prevalence of dementia increased almost steeply with advancing age for both sexes (Table 1). The overall prevalence was 5.7 for AD, 0.6 for VD, 4.5 for mixed dementia and 1.7 for other dementias (Table 1). The prevalence of AD was higher in women than in men (Table 1). One patient with Parkinson's disease and one with progressive supranuclear palsy were included the category of other dementias. We could not find any patient who met the criteria for DLB and FTLD.

Table 1.  Age- and sex-specific prevalence (cases/100) of dementia of all types, and overall sex-specific prevalence by type of dementia in Campo Grane, 1 August, 2000
 MenWomenBoth sexes
 CasesPopulation
at risk
Prevalence
(%)
CasesPopulation
at risk
Prevalence
(%)
CasesPopulation
at risk
Prevalence
(%)
Dementia of all types
70–74 years1293.40320.01611.6
75–79 years1224.52248.33466.5
80–84 years1911.131520.042416.7
85–89 years2633.32922.241526.7
90–94 years3475.04590.07977.8
95–100 years000.0020.0020.0
Total87011.4118712.61915712.1
Alzheimer's disease
70–100 years3704.26876.991575.7
Vascular dimentia
70–100 years1701.40870.011570.6
Mixed
70–100 years3704.24874.671574.5
Other dementia
70–100 years1701.41870.621571.3

All seven cases with mixed dementia (AD/VD) had a similar clinical course of AD associated with focal neurologic symptoms and evidence of relevant ischemic changes by CT scan. Two cases had so-called poststroke dementia, but their dementia is progressive and cognitive impairment prior to stroke had been suspected. Furthermore, in these seven cases, severe white matter disease was detected by CT scans.

Scores of the MMSE scale were 0–21 in AD, 2 in VD, 13–20 in mixed dementia, with the greatest number of patients being at a moderate stage (MMSE: 10–19). Eleven cases (five AD, one VD, five mixed dementia) had hypertension and one AD case had diabetes.

DISCUSSION

Although it is believed that overall dementia rates are generally similar among countries, many previous papers suggested significant regional differences in type, with the Japanese, Chinese and Russian studies reporting higher rates of VD than AD, while studies from most Western countries showed either no significant difference or significantly higher rates of AD than VD.4 Most Japanese surveys done in past years have reported AD/VD ratios of less than 1.23 However, several recent studies in Japan showed higher ratios of AD/VD, similar to those in Western countries.9,11 Our previous study in Amino-cho also revealed that the ratio was 2.1,24 the highest among the previous Japanese reports, but was very similar to that found for Kaokaoping in southern Taiwan.25 A study from Korea showed a very high prevalence of dementia and a high AD/VD ratio.26 Also two studies of older Japanese-Americans in Hawaii and in King County found the ratios of 1.527 and 2.5.28 In the 7 year follow-up Hisayama study, the recent prevalence of VD and the incidence of stroke was found to be decreased in men, which suggested that the incidence of VD may decrease as the risk of stroke is decreased.29 Prevalence estimates of AD rise exponentially with age.7,23 In Japan, the average life expectancy is much prolonged. The increasing AD/VD ratio may be due to these factors.

The present study showed that the prevalence of all types of dementia in the elderly population over 70 years was 12.1 in the Japanese-Brazilian community. As shown in Table 2, this prevalence rate was higher than previously reported in Japanese communities including Okinawa,6,8,24,30–32 or in Japanese-American communities.27,28 A similar prevalence rate has been shown in a Hiroshima study,32 but the subjects were selected from atomic bomb survivors. A remarkable difference of the dietary pattern between Japan and Brazil has been reported.15,16 Mizushima et al. confirmed a lower frequency of fish intake by Japanese-Brazilians (immigrants from Okinawa) compared with Japanese living in Okinawa.15,16 Furthermore, a lower value of n-3 polyunsaturated fatty acids (PUFA) in plasma in Japanese-Brazilians has been shown.16 In a Rotterdam study, fish consumption has been inversely related to the incidence of dementia, especially AD.13 The n-3 PUFA in fish have anti-inflammatory properties,33 and inflammation has now been believed to be closely related with AD pathoetiology.34 Lowered levels of n-3 PUFA docosahexaenoic acid in AD were also reported in a human autopsy study.35 Therefore, the higher prevalence of dementia in Japanese-Brazilians than in elderly people in Japan may, in part, be attributed to this dietary risk factor.

Table 2.  Prevalence of dementia and per cent of dementia subtypes in the population aged over 70 years in six Japanese areas, Korea, Taiwan, Hawaii (Japanese-American), King county (Japanese-American) and Campo Grande (Japanese-Brazilian)
Survey
year
SitePopulation
at risk
Prevalence
(%)
Alzheimer's
disease (%)
Vascular
dimentia (%)
Mixed (%)Reference
  • *

    Subjects were only men aged 71 to 93 years. NA, not available.

1980Daisen8106.248NANA8
1985Hisayama6088.8NANANA6
1990Toyama9556.341.030.1NA30
1991Okinawa22177.3NANANA31
1998Amino25495.257.826.32.224
1999Hiroshima119511.850.723.92.132
1990Myun (Korea)39817.146.79.9NA26
1993Kaokaoping (Taiwan)17175.456.021.5NA25
1991Hawaii (USA)3734*9.330.521.711.127
1992King County (USA)12458.355.322.3NA28
2000This study (Brazil)15712.147.35.236.8

There is increasing evidence of a complex relationship between VD and AD. So far it is believed that cases of pure VD is less common than had been widely assumed.36–38 There is often a vascular component in the pathogenesis of dementia, including AD.39 Some treatments appear to be equally effective in AD and VD.40 Thus, these considerations have the potential to result in an increased prevalence of mixed dementia. In the present study, all cases diagnosed as mixed dementia had similar clinical courses of AD associated with focal neurologic symptoms and evidence of relevant ischemic changes by CT scan. As shown by several studies, these cases might represent a mixed pathology of AD and VD.37,41 The precise reason for the prevalence of mixed dementia being high in Japanese-Brazilians compared with that in the Amino study evaluated by the same criteria25 remains unknown. A high risk for vascular diseases, as suggested by previous reports,15,16 might be one reason.

ACKNOWLEDGEMENT

This work was supported in part by Grants-in-Aids for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan.

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