Association Between Migration and Cognitive Function Among Middle Aged and Older Adults: a Comparison Between China and India

Migration is a fundamental demographic process that has been linked to cognitive function among the immigrant populations in developed countries. However, there is limited understanding of how migration and cognitive function are related among internal migrants in developing countries. The purpose of this dissertation is to provide some of the first evidence of the association between rural-urban migration and cognitive function among middle aged and older adults in China and India. We also examined whether the association between migration and cognitive function can be explained by a variety of factors such as sociodemographic background, health behaviors, and physical health status.

We first conducted a comprehensive review of the literature on the association between migration and cognition among middle-aged and older adults. Based on the current evidence, we developed a general conceptual framework to understand the factors contributing to the association. We identified five potential mechanisms from the literature: 1) socioeconomic status, 2) psychosocial factors, 3) behavioral factors, 4) physical and psychological health status, and 5) environmental factors. We also included several underlying factors in this conceptual framework such as early-life conditions, gender, and genetic factors. Overall, we found that factors linking migration and cognitive function are multidimensional and complex. We encouraged future studies to further test these mechanisms and refine this framework using empirical data.

To examine the association between migration and cognitive function among the internal migrant populations in China and India, we conducted a cross-national comparison study using the 2007-2010 World Health Organization Study on global AGEing and adult health (SAGE) data. We included 12,937 adults aged 50 or over from China and another 6,244 from India. We categorized migration status into six groups: urban residents, rural residents, urban-to-urban migrants, rural-to-urban migrants, rural-to-rural migrants, and urban-to-rural migrants. We generated a global cognitive function score by combing the following five cognitive tests: immediate and delayed recall tests, digit span tests (forward and backward), and verbal fluency test. We also assessed a variety of covariates in the analyses that included sociodemographic characteristics, psychosocial factors, health behaviors, and physical health status.

In the Chinese sample, we found that urban residents and urban-to-urban migrants had the highest level of cognitive function; whereas rural residents and rural-to-rural migrants had the poorest cognitive function. Our findings also showed that people who migrated to/within rural areas before age 20 had poorer cognitive function than those who migrated later in their adulthood. We found similar association in the Indian sample that urban residents and urban-to-urban migrants had the highest levels of cognition; while rural residents and people who migrated to (or within) rural areas had the poorest cognitive function. In both countries, we found that these patterns remain largely unchanged after adjusting for multiple study covariates.

In this dissertation, we also assessed gender differences in the association between migration and cognitive function. While doing a cross-country comparison, we observed a consistent female disadvantage in cognitive function in both countries. We found that female rural residents and female rural-to-rural migrants had the poorest cognitive function in both the Chinese and Indian samples. Among Chinese men, we found that rural residents had poorer cognitive function than urban residents, while urban-to-urban migrants had the highest level of cognition; however, for male counterparts in India, rural-to-rural migrants had the lowest level of cognitive function.

In sum, we found that cognitive function among middle aged and older adults in China and India differ significantly according to their migration status. The association between migration and cognitive function is complex and differs by gender and country.