Association between body mass index and cause-specific mortality as well as hospitalization in frail Chinese older adults.

Aim: A U-shaped relationship between body mass index (BMI) and all-cause mortality has been reported, but there are few studies examining the association between BMI and cause-specific mortality and hospitalization. We carried out a longitudinal study to examine these associations in Chinese older adults with multiple comorbidities, which could provide a reference for the recommended BMI in this population.

Methods: From 2004 to 2013, a retrospective cohort of Chinese older adults was selected from a geriatric day hospital in Hong Kong. They were divided into groups according to their BMI: BMI <16; BMI 16-18; BMI 18.1-20; BMI 20.1-22; BMI 22.1-24; BMI 24.1-26; BMI 26.1-28; BMI 28.1-30 and BMI >30. Other assessments included medical, functional, cognitive, social and nutritional assessment.

Results: A total of 1747 older adults (mean age 80.8 ± 7.1 years, 44.1% male, 46.1% living in nursing homes, Charlson Comorbidity Index 2.0 ± 1.6) with a median follow up of 3.5 years were included. Older adults with BMI 24-28 had the lowest all-cause, infection-related and cardiovascular mortality (P < 0.001). Multivariate analysis showed that there was an inverted J-shaped association between BMI and hazard ratio for all-cause and infection-related mortality in both nursing home and community-dwelling older adults. The rate of all-cause hospitalization was lower in older adults with BMI 22-28 (P = 0.002). Multivariate analysis showed that there was an inverted J-shaped association between the odds ratio of recurrent hospitalization and BMI.

Conclusion: Chinese older adults with BMI 24-28 had lower all-cause mortality, infection-related mortality, cardiovascular-related mortality and all-cause hospitalization. This study provides a reference for the recommended BMI in this population.