The time trends of cognitive impairment incidence among older Chinese people in the community: based on the CLHLS cohorts from 1998 to 2014

Objective: to examine a 16-year trend in cognitive impairment (CI) incidence and associated factors among older Chinese people. Subjects: aged 60 and above whose cognitive function were normal at their first test. Methods: a secondary analysis that identified subjects from the database of Chinese Longitudinal Healthy Longevity Survey (CLHLS). The database contained mixed longitudinal cohorts of older Chinese people surveyed in 1998, 2000, 2002, 2005, 2008-09, 2011-12 and 2014. The cognitive function of subjects was tested using the Chinese Mini-Mental State Examination (CMMSE) in each wave. The unique individual code identified a mixed cohort of 17,896 subjects who had multiple CMMSE measures over a 16-year period and available covariates for the analysis. CI was defined as the CMMSE score below 18 points. Crude and age-standardised incidence of CI by gender were calculated by year of survey. Risk factor adjusted time trends in the incidence were examined using multilevel regression models. Results: age-standardised CI incidence decreased from 58.77 parts per thousand to 10.09 parts per thousand (P < 0.001) from 1998 to 2014, and this decrease remained after adjusting for covariates. About 15.8% in the observed decline was explained by higher education, and 7.9% was due to health practice (regular exercise, physical activity and cognitive activity), beyond age and gender effects. Conclusion: the CI incidence among older Chinese people decreased from 1998 to 2014. Lower education level and less frequent health practices mentioned above were important risk factors in CI prevention.