Body mass index trajectories and all-cause mortality in older Chinese adults: Hong Kong's Elderly Health Service Cohort

Background Weight loss at older ages appears to be associated with higher mortality in Western and some East Asian countries, despite differences in the prevalence of obesity; whether it is relevant to China is unknown. We examined the association of body mass index (BMI) trajectories with all-cause mortality in older Chinese adults by sex and baseline age (65-69 years, 70+ years).Methods 54 160 participants aged 65 or above from Hong Kong's Elderly Health Service Cohort with at least five BMI measurements were included. We identified distinct BMI trajectories using group-based trajectory modelling. We assessed the associations of BMI trajectories with mortality risk using a Cox model stratified by sex and age.Results Compared with 'normal weight, stable', the 'low-normal weight, decreasing' had higher mortality risk in both sexes and age groups (eg, HR 1.43, 95% CI 1.24 to 1.66 in men aged 65-69 years). The 'overweight, stable' and 'obese, stable' had lower mortality risk, especially in men at older ages. However, the proportion in the 'low-normal weight, decreasing' was greater at 70+ years than at 65-69 years, while the proportion in the 'overweight, stable' and 'obese, stable' was lower in the older group.Conclusions Decreasing BMI is a likely symptom of ill health in older adults. Inconsistency between the risks and the proportion in each BMI trajectory group by age suggests the observed associations could be driven by changes in weight and preferential recruitment of survivors. Maintaining a healthy weight remains relevant at older ages.