Prevalence of dementia has been reported based on several population based epidemiological studies conducted across India over the last two decades. According to the Dementia India Report 2010 (Alzheimer’s and Related Disorders of India [ARDSI], 2010) projections, an estimated 5.29 million Indian people aged over 60 have dementia. The more recent Global Burden of Disease study estimated that 3.69 million people had Alzheimer’s disease or other dementias in India in 2019 (India State-Level Disease Burden Initiative Neurological Disorders Collaborators, 2021). There is variability in reported prevalence rates ranging from 0.3% (Rodriguez et al., 2008) to 14.9% (Seby et al., 2011) among older adults, depending on the sample size, age of the cohort, geographical area considered (rural vs. urban population) and the year of the study (Table 6.1). Meta-analysis of individual studies have reported pooled prevalence estimates for dementia to range from 3.4% (95% CI = 2.0 to 5.0) to 4.4% (2.2-7.2) in India (Dhiman et al., 2021; Farina et al, 2020).

Differences in estimates may be related to the adoption of different methods and defining criteria, but differences in environmental and genetic risk factors may also contribute. Recognising the need to study dementia prevalence using a uniform method, the Government of India’s scientific research funding agency, specifically the Department of Biotechnology, has initiated a multi-centric study across rural, urban, and tribal areas to observe dementia prevalence (Bhatt, 2020).

Table 6.1 shows dementia prevalence across the country

S.No	Publication	Location	Age of population surveyed	Number screened	Screening tool	Confirmation tool	Prevalence of dementia
1	Razdan et al., (1994) Neuroepidemiology	Rural Kashmir	All	63,645		Neurological examination	No dementia was found
2	Shaji et al., (1996) The British Journal of Psychiatry	Rural Kerala	≥60 years	2067	Vernacular adaptation of the Mini Mental State Examination.   Score of 23 and below -a detailed neuropsychological evaluation by CAMDEX-Section B.	DSM-III-R criteria for dementia   Subcategorisation of dementia was done based on ICD-10 diagnostic criteria	33.9 per 1000
3	Rajkumar, Kumar and Thara (1997) International Journal of Geriatric Psychiatry	Rural Tamil Nadu	≥60 years	750	Geriatric Mental State schedule (GMS).		3.5%
4	Chandra et al., (1998) Neurology	Rural Haryana	≥55 years	5126	Hindi cognitive and functional screening instruments, developed for and validated in this population.	DSM- IV diagnostic criteria, Clinical Dementia Rating Scale (CDR), National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria.	≥55 years: 0.84% ≥65 years: 1.36%
5	Vas et al., (2001) International Psychogeriatrics	Urban Maharashtra	≥40 years	24,488	Self-report or interviewer-rated protocols based on the Sandoz Clinical Assessment Geriatric Scale.   “A score +2 SD above the mean were screened for cognitive functioning using a modified and translated version of the Mini Mental State Examination”	Detailed neurological, psychiatric, and neuropsychological evaluation as well as  laboratory investigations and other tests etc.   DSM-IV diagnostic criteria.	≥40 years: 0.43%   ≥65 years: 2.44%
6	Shaji, Bose and Verghese (2005) The British Journal of Psychiatry	Urban Kerala	≥65 years	1934	Vernacular adaptation of the Mini-Mental State Examination	Diagnoses according to DSM-IV criteria. Identified cases were categorised by ICD-10 criteria.	33.6 per 1000
7	Das et al., (2006) The Indian Journal of Medical Research	Urban West Bengal	≥50 years	52,377	National Institute of Mental Health and Neurosciences (NIMHANS) used questionnaire.   A modified version of “Cognitive Battery” used by Ganguli et al.	DSM-IV criteria	87.82 per 100,000 population
8	Rodriguez et al., (2008) Lancet	Urban/Rural Tamil Nadu	≥65 years	Urban: 1005   Rural: 999	10/66 dementia diagnostic algorithm and by computerised application of dementia criterion from the DSM-IV.		10/66 standardized prevalence:   Urban: 8.2%   Rural: 8.7%   DSM-IV dementia standardized prevalence:   Urban: 0.9%   Rural: 0.3%
9	Das et al., (2008) The Journal of the Association of Physicians of India	Urban West Bengal	≥60 years	5430	National Institute of Mental Health and Neurosciences (NIMHANS) developed questionnaire.   A modified version of “Cognitive Battery” developed by Ganguli et al.	DSM-IV criteria and for “individual subtypes the standard Definitions of NINDS-ADRDA” were used.	≥60 years: 7.89 per 1000 elderly
10	Banerjee et al., (2008) Neuroepidemiology	Urban West Bengal	≥50 years	6129	Screening questionnaire   Kolkata Cognitive Test Battery	DSM-IV criteria	≥50 years: 0.62% ≥60 years: 1.25%
11	Raina et al., (2008) Annals of Indian Academy of Neurology	Migrant community cluster of Jammu city Kashmir	≥60 years	200	Kashmiri version of the Mini-Mental State Examination   A functional ability questionnaire- Everyday Abilities Scale for India (EASI)	Clinical evaluation was carried out by a neurologist.   Patients diagnosed with dementia  further underwent detailed laboratory investigations and MRI scan.	6.5%
12	Mathuranath et al., (2010) International Journal of Geriatric Psychiatry	Urban Kerala	≥55	2466	Addenbrooke’s cognition examination (ACE) (Mathuranath et al., 2000), a cognition screening battery like the CERAD screening battery.   An instrumental activities of daily living scale for the elderly (IADL-E)	A semi-structured family interview with family members.   The evaluations included:   a) Cognition and behavioural symptoms (over past month).   b) Clinical evaluation.   c) Neuropsychological evaluation.   d) Further evaluation – screening blood investigations and/or neuroimaging tests.   DSM-IV criteria used to diagnose dementia.	≥65 years: 4.86%
13	Saldanha et al., (2010) Indian Journal of Psychiatry	Urban Maharastra	≥65	2119	Mini Mental State Examination (MMSE   ‘Cognitive test component’ of the 10/66 research groups instrument – community screening instrument for Dementia (CSI-D),	ICD-10 Diagnostic Research Criteria.	≥65 years: 4.1%
14	Seby, et al., (2011) Indian Journal of Psychiatry	Urban Pune – Maharashtra	>65	202	Hindi version Mini-Mental State Examination (MMSE)		14.9%
15	Poddar et al., (2011) Annals of Indian Academy of Neurology	Urban and Rural Uttar Pradesh	≥50 years	2890	Hindi version of the Mini Mental State Examination (MMSE)		5.1%
16	Raina et al., (2014) North American Journal of Medical Sciences	Urban, Rural, Tribal Himalaya	≥60 years	2000	Hindi Mental State Examination (HMSE)	Detailed clinical history.   Subjects examined for cognitive or intellectual, functional, and  psychiatric or behavioural symptoms.	1.6%
17	Raina, Chander and Bhardwaj (2016) Journal of Neurosciences in rural practice	Tribal Himachal Pradesh	≥60 years	481	Bharmouri Mental State Examination [BMSE]	The clinical evaluation was carried out by a neurologist.	No dementia
18	Banerjee et al., (2017) International Journal of Geriatric Psychiatry	Urban Bengal	≥60 years	100,802	Two dementia pertinent questions to family members   Detailed clinical history   Kolkata Cognitive Screening Battery	DSM-IV criteria for dementia	1.53%

Table Source: (Razdan et al., 1994;  Shaji et al., 1996; Rajkumar, Kumar and Thara, 1997; Chandra et al., 1998; Vas et al., 2001; Shaji, Bose and Verghese, 2005; Rodriguez et al., 2008; Das et al., 2006; Das et al., 2007; Das et al., 2008; Raina et al., 2008; Mathuranath et al., 2010 ; Saldanha et al., 2010; Seby, Chaudhary and Chakraborty, 2011, Poddar et al., 2011; Raina et al., 2014; Raina, Chander and Bhardwaj, 2016; Banerjee et al., 2017).

Moreover, there are few studies reporting incidence of dementia in India and results are varied (Table 6.2).

Table 6.2 shows studies reporting incidence rates for dementia in India

S.No.	Publication	Method	Screening tool	Confirmation tool	Incidence
1.	Chandra et al., 2001, Neurology	28 villages in Haryana (North India) 2 years.	Hindi cognitive screening battery based on the Consortium to Establish a Registry for AD (CERAD) neuropsychological panel.	DSM-IV criteria and the Clinical Dementia Rating scale CDR	Incidence rates per 1000 persons-years for AD: 3.24 (95% CI: 1.48-6.14) for those aged ≥ 65 years. 1.74 (95% CI: 0.84-3.20) for those aged ≥55 years. Standardised against the age distribution of the 1990 US Census, the overall incidence rate in those aged 65 years was 4.7 per 1000 person-years.
2.	Mathuranath et al., 2012, Neurology India	4 urban and semi-urban regions of Trivandrum city in Kerala.	Malayalam Addenbrooke’s cognitive examination (mACE).	Clinical evaluation by neurologist based on the DSM-IV criteria.	Incidence rates per 1000 person-years for AD: 11.67 (95% CI: 10.9-12.4) for those aged ≥55 years. 15.54 (95% CI: 14.6-16.5) for those aged ≥65 years. Standardised against the year 2000 U.S. Census, the age-adjusted incidence rate was 9.19 (95% CI: 9.03-9.35) per 1000 person-years.
3.	Banerjee et al., 2017, Int Journal of GerPsychiatry	Kolkata, West Bengal	Two dementia pertinent questions to family members.   Detailed clinical history   Kolkata Cognitive Screening Battery	DSM-IV criteria	Average annual incidence rate of dementia was 72.57 per 100,000 ≥ 55 years age.

Source: (Chandra et al., 2001; Mathuranath et al., 2012; Banerjee et al., 2017)

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