Prevalence of cognitive impairment and dementia in older adults living at high altitude: A systematic review and meta-analysis

Introduction: Dementia is a chronic disease with a variable prevalence throughout the world; however, this could be higher at high-altitude populations. We aimed to summarize the prevalence of cognitive impairment and dementia in older adults living at high altitude. Methods: We searched in PubMed, Medline, Scopus, Web of Science, and Embase and included the studies published from inception to July 20, 2020, with no language restriction, which reported the frequency of cognitive impairment or dementia in older adults living at high-altitude populations. Random-effects meta-analyses were performed to calculate the overall prevalence and 95% confidence intervals (95% CI) of cognitive impairment and dementia. The risk of bias was evaluated using the Newcastle-Ottawa Scale (NOS) adapted for cross-sectional studies. Results: Six studies were included (3,724 participants), and 5 of the 6 included studies were carried out in Latin America. The altitude ranged from 1,783 to 3,847 m, the proportion of women included varied from 38.7 to 65.6%, and the proportion of participants with elementary or illiterate educational level ranged from 71.7 to 97.6%. The overall prevalence of cognitive impairment was 22.0% (95% CI: 8-40, I²: 99%), and the overall prevalence of dementia was 11.0% (95% CI: 6-17, I2: 92%). In a subgroup analysis according to the instrument used to evaluate cognitive impairment, the prevalence of cognitive impairment was 21.0% (95% CI: 5-42, I2: 99%) in the MMSE group while the prevalence was 29.0% (95% CI: 0-78) in the non-MMSE group. Conclusions: The prevalence of cognitive impairment and dementia in older adults living at high altitude is almost twice the number reported in some world regions.