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Association between Body Mass Index and Cognitive Function among Chinese Nonagenarians/Centenarians

Aims: We examined the individual association between body mass index (BMI) and cognitive function among the very elderly. Methods: The present study analyzed data from a survey that was conducted on all residents aged 90 years or more from a district which had 2,311,709 inhabitants in 2005. The subjects were divided into 4 groups according to quartiles of BMI (<16.6, 16.6–18.9, 18.9–21.1 and >21.1), and according to classification criteria of underweight, normal weight, overweight and obesity in BMI (<18.5, 18.5–23.0, 23.0–27.5 and >27.5), respectively. Results: The subjects included in the statistical analysis were 211 men and 427 women. Those in the 3rd quartile of BMI (18.9–21.1) had higher cognitive function scores (p < 0.001) and were less likely to present possible dementia (p = 0.016) than the others. However, there was no difference in cognitive function scores (p = 0.350) or prevalence of possible dementia (p = 0.263) among obesity, overweight, normal weight and underweight groups. Conclusions: Concerning longevity in Chinese, there is an association between BMI and cognitive function. BMI of around 20 (18.9–21.1) is associated with the lowest risk of prevalence of possible dementia and the highest cognitive function scores.