Introduction to LASI-DAD: The Longitudinal Aging Study in India-Diagnostic Assessment of Dementia

This supplement is designed to introduce the Longitudinal Aging Study in India-Diagnostic Assessment of Dementia (LASI-DAD) to the international research community. LASI is a prospective multi-purpose population survey of more than 70,000 adults aged 45 and older, representative of both the entire country and each state of India,¹ and LASI-DAD is an in-depth study of late-life cognition and dementia, drawing a subsample of over 3,000 older adults aged 60 and older from LASI. It is one of a family of population-based cognitive impairment and dementia studies using the Harmonized Cognitive Assessment Protocol (HCAP) that includes the Health and Retirement Study (HRS)² and its sister data sets around the world.

The HCAP consists of a pair of in-person interviews, one with the target respondent and one with an informant named by the respondent. The respondent interview includes a neuropsychological test battery designed to measure a range of key cognitive domains affected by cognitive aging, such as memory, language, attention, executive function, and visuospatial skills. The HCAP studies share core elements such as targeted cognitive domains, specific cognitive tests, questions for informants, and method of data collection. Given differences in educational levels and across countries, LASI-DAD has modified the protocol where needed and included additional cognitive tests suitable for illiterate and innumerate populations.

LASI-DAD is also unique in that it collects rich biological and clinical information through venous blood assays, geriatric assessment, and clinical diagnosis of dementia status. The overarching goal of LASI-DAD is to advance dementia research to better understand late-life cognition and dementia and their risk factors. For this goal, we collect rich data on risk factors through venous blood assays and geriatric assessment. In common with the HCAP studies, the data are archived and available to all researchers. From 14 states of India, 3,224 community-dwelling persons aged 60 and older participated in the baseline interview, and follow-up longitudinal interviews are planned every 4 years. Data were collected from October 2017 through May 2019 and archived in August 2019. The response rates were 82.9% for the respondent interview and 82.0% for the informant interview.

The purpose of this supplement is to introduce LASI-DAD to the international research community, describe comparability with the HCAP studies, and showcase the potential of LASI-DAD, particularly for researchers in geriatric medicine. We hope to encourage researchers around the world to exploit this valuable data set.

The first article in this supplement describes the design and methodology of the study, the sample design, fieldwork procedures, response rates, and weighting process, and it introduces soon-to-be available data on exposure to air pollution and genotyped data.³

The second article describes the psychometric properties of cognitive tests used, in particular the factor structure of the cognitive test battery and its conformity with a model of cognition developed based on the English-speaking samples.⁴ The authors demonstrate its conformity and conclude that clinically and for research purposes, the broad domains of memory, executive functioning, orientation, visuospatial ability, and language/fluency can be used to classify cognitive impairment and to make comparisons with cognition measured in other HCAP studies.

The third article examines sex differences in late-life cognition and investigates the determinants of observed gaps, focusing explicitly on early-life human capital investment of nutrition and education.⁵ The findings that lower levels of early-life human capital investments in nutrition and education among women led to female disadvantage in late-life cognition has important implications for public health policy aiming at reducing dementia.

The fourth article investigates the relationship between cognition and a key cardiovascular risk factor, namely hypertension.⁶ It provides a more nuanced understanding of diagnosed and undiagnosed hypertension in India, rather than depending solely on clinical diagnosis, and of the complex relationship with cognition, which is likely affected by access to health care and education, among other factors. The authors reported a high prevalence rate of 62% of hypertension among the aged 60 and older population with one-third of them undiagnosed, but they did not find a statistically significant association between hypertension and cognition.

The fifth article describes the comparability of LASI-DAD data with that of the HRS-HCAP and shows that the distribution of cardiometabolic risk factors differs significantly between India and the United States.⁷ At the same time, in both countries several cardiometabolic-inflammatory risk factors were found to be consistently associated with cognitive functional levels. Cognitive functioning was lower among those with high homocysteine and pro-B-type natriuretic peptide levels, and among those with low albumin levels in both countries. However, the association between hemoglobin A_1c and cognition was found to trend in the opposite direction, and this puzzling result calls for future research.

The sixth article investigates genetic factors, examining whether risk loci identified in European ancestry populations have similar effects in the Indian population and reports modest association.⁸ Discrepancies in allele frequencies and cognitive association results suggest that genetic factors identified from European ancestry may play a limited role for South Asians, raising the critical importance of a more comprehensive assessment of the genetic architecture of the Indian population.

The final article introduces online clinical consensus diagnosis, a cost-effective alternative to the typical in-person clinical diagnosis consensus conference, and presents the results from a validation study.⁹ This demonstrates that online clinical consensus diagnosis based on the HCAP interview data yields results consistent with the in-person clinical assessment and diagnosis. This innovative approach proves its potential to bring clinical adjudication into other epidemiological studies.

Archived LASI-DAD data can be accessed on its website (lasi-dad.org) by making an application to the Gateway to Global Aging Data (g2aging.org).