Dementia in a tribal landlocked elderly population at high altitude: What explains the lower prevalence?

Introduction

In health and diseases research, epidemiological studies among tribal populations at high altitude open an interesting research window to understand the evolution of response of factors associated to disease causing agents.[1] Previously, we reported on the prevalence of dementia in elderly population in migrant, urban, rural, and tribal populations of Himachal Pradesh state in North India.[2] The present study was conducted with a view to estimating the prevalence of dementia in Tribal Landlocked Elderly population at high altitude and therefore to draw some conclusions on the differential distribution of dementia across populations.

The scheduled tribe population of Himachal Pradesh constitutes about 4.02% of its total population with major concentration in the districts of Kinnaur and Lahaul-Spiti and parts of the district Chamba.[3] The Kinnaur and Lahaul-Spiti districts, in their entirety, and Pangi and Bharmour (tehsil Bharmour and sub-tehsil Holi) subdivisions of Chamba district constitute the scheduled areas in the state. In our previous study, we reported on the prevalence of dementia in an elderly population Bharmour, at an altitude of 7000 feet (2134 m) with a predominant transhumant agro-pastoralist community.[4] The current study was based on a predominantly agricultural tribal population at a higher altitude.

Methods

All individuals aged 60 years and above from Pangi were the target population screened. A stratified simple random technique was used to include participants for this study. All the villages from Sural Batori valley (10,000 feet; 3048 m) and Chasak Batori valley (12,000 feet; 3658 m) were stratified to two groups of villages. Villages from each group were selected using random number table so that about 300 eligible individuals could be selected from each of the two altitude group. The aim was to screen at least 500 individuals above 60 years of age to establish a comparison with data obtained from our previous study. A higher number was chosen to account for nonwillingness of individuals to participate in the study. In the selected villages, all eligible subjects consenting to participate in the study were screened. A total of 481 individuals agreed to participate in the study, giving us a response rate of 80%. Thus, a total of 481 participants aged 60 years and above were included in this study.

Details on education, occupation, current marital status, and type of family were enquired from the all the participants. Only a full-time homemaker was regarded as a homemaker, whereas a homemaker who also worked as an agriculturist was classified as agriculturist.

Results

The details of the study population are provided in Table 1. The population sample consisted of 295 (61.3%) males and 185 (38.7%) females. Majority (401/485; 83%) of the participants were <75 years of age. Importantly, however a good percentage (8.3%; 40/481) of study participants was above 80 years of age pointing to a fair distribution of study participations across demographic dividend. Majority of elderly (81.4%; 392/481) participants were illiterate. Almost all (98.4%; 183/186) female participants were illiterate. Only 2 (0.7%) out of a total of 481 participants had completed graduation.

Table 1 Sociodemographic profile of study population

Table 2 provides a detail of the participants on Bharmouri Mental state examination (BMSE). Importantly, no individual more than 60 years of age in the population studied scored <18 on the cognitive screen. Six participants out of a total of 481 scored between 18 and 23 on cognitive screen thus were classified as cases of MCI. Two cases (2/38; 5.3%) were in the 65–69 years of age group and four cases (4/17; 23.5%) were in the 75–79 years of age group. All cases of MCI were illiterate.

Table 2 Distribution of study subjects according to BMSE score

Discussion

There is a scarcity of data on dementia from the least developed areas of the less developed regions of sub-Saharan Africa and South Asia. The present study based in a tribal area landlocked area of North-West India aimed the estimating prevalence of dementia in least developed areas and thereby attempt to generate a hypothesis on potential preventive factors responsible for differential distribution of dementia across populations.

A growing body of the epidemiological literature suggests that lower levels of education are associated with higher prevalence of dementia and lack of education may be a risk factor for Alzheimer's disease (AD).[7] If there is a genuine difference in risk, one would expect to find higher prevalence rates of AD in societies with lower educational levels, perhaps in pandemic proportions in populations with no formal education.[8] The present study points to the contrary. The present study population is predominantly illiterate. The present study therefore, in its findings accentuates the findings of our previous study which suggested that the differences between the prevalence rates for dementia across populations appear to be a function of a valid regional difference.

Studies in past have also suggested that societies living in isolated hilly and tribal areas seem less predisposed to dementia particularly age-related neurodegenerative and vascular dementia, which are the most common causes for dementia in elderly. This may be because some environmental risk factors are much less prevalent in these settings.

A recent study points to changes in vascular risk factors concomitant with change in prevalence of dementia without concluding on the role of education as a factor for reduction in dementia incidence, if any in recent years.[9] Another study from Switzerland suggested a link between a decline in the age-adjusted burden of amyloid deposition and changes in education levels.[10] It further reflects on the role of diet, physical activity, exposures to environmental toxins, or other unknown factors in reduction in amyloid deposition. The study is similar to the findings of data on dementia derived from Framingham Heart Study.[9]

Our studies on dementia point to similar findings. The prevalence of cardiovascular risk factors such as hypertension in this tribal area has been found to be much lower than the rural and urban areas of Himachal Pradesh thus pointing to a role of hypertension as a contributor to dementia.[1]

Importantly, the fundamental similarity between the two tribal populations studied by us and recording a lower prevalence of dementia is the presence of variety of foods such as barley, wheat, maize, and phulan as staple foods in comparison of largely wheat and rice dependent populations in rural and urban India. A similarity of our findings can be drawn with the Kashmir valley study conducted in Kuthar area of Kashmir.[11] The food habits of that population are almost similar to that of this population with an abundance of apples and walnuts. Identification of diet and environmental factors may be the key in identifying factors preventing dementia.