Prevalence of Alzheimer's disease and other dementias in rural India: the Indo-US study

A review of the epidemiological transition in dementia--cross-national comparisons of the indices related to Alzheimer's disease and vascular dementia

OBJECTIVE

To examine temporal changes in the prevalence of dementia and associated factors.

METHOD

All publications on the epidemiology of dementia were identified using a medline search for the years 1966-1999.

RESULTS

Alzheimer's disease (AD) has become nearly twice as prevalent as vascular dementia (VaD) in Korea, Japan, and China since transition in early 1990s. Prior to this, in the 1980s, VaD was more prevalent than AD in these countries. In Nigeria, the prevalence of dementia was low. Indian studies were contradictory, with both AD and VaD being more prevalent in different studies. American and European studies consistently reported AD to be more prevalent than VaD.

CONCLUSION

A theoretical model of transition from low incidence-high mortality society to high incidence-high mortality society to low incidence-low mortality society may explain these findings. Rigorous testing in prospective, longitudinal and population-based cross-national studies using culture-fair diagnostic instruments is required.

Patients with Alzheimer's disease have reduced activities in midlife compared with healthy control-group members

The development of Alzheimer's disease (AD) later in life may be reflective of environmental factors operating over the course of a lifetime. Educational and occupational attainments have been found to be protective against the development of the disease but participation in activities has received little attention. In a case-control study, we collected questionnaire data about 26 nonoccupational activities from ages 20 to 60. Participants included 193 people with probable or possible AD and 358 healthy control-group members. Activity patterns for intellectual, passive, and physical activities were classified by using an adaptation of a published scale in terms of "diversity" (total number of activities), "intensity" (hours per month), and "percentage intensity" (percentage of total activity hours devoted to each activity category). The control group was more active during midlife than the case group was for all three activity categories, even after controlling for age, gender, income adequacy, and education. The odds ratio for AD in those performing less than the mean value of activities was 3.85 (95% confidence interval: 2.65-5.58, P < 0.001). The increase in time devoted to intellectual activities from early adulthood (20-39) to middle adulthood (40-60) was associated with a significant decrease in the probability of membership in the case group. We conclude that diversity of activities and intensity of intellectual activities were reduced in patients with AD as compared with the control group. These findings may be because inactivity is a risk factor for the disease or because inactivity is a reflection of very early subclinical effects of the disease, or both.

Epidemiology of dementia: concepts and overview

This article reviews current knowledge about the prevalence and incidence of dementia and the risk and protective factors for dementia. Relevant epidemiologic concepts and methodological issues are reviewed, focusing on the implications of designing and interpreting epidemiologic studies of dementia and illustrating the integrative role of epidemiology.

Methodological issues for population-based research into dementia in developing countries. A position paper from the 10/66 Dementia Research Group

The 10/66 Dementia Research Group has been formed to promote good-quality, internationally comparable research into dementia in developing countries through active research collaboration. In this position paper, we review existing research into dementia prevalence in developing regions of the world. Seven methodologically robust studies were identified. The prevalence of dementia, age-adjusted to the age structure of the Kerala population, ranged from 1.3% to 5.3% for all those aged 60 or over and from 1.7% to 5.2% for all those aged 65 and over. Two studies, from Ibadan, Nigeria and Ballabgarh, India, reported strikingly low prevalence figures. The reported prevalence for most studies was somewhat lower than the consistent figures for Europe reported by the EURODEM concerted action. Based on critical review of the literature, and on the practical research experience of members of the 10/66 group, recommendations have been made for procedure in the following areas: age limits for inclusion in dementia surveys, age ascertainment, sampling, scope for incidence studies, functional assessment and culture- and education-fair dementia diagnosis.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.