Dietary protein intake and all-cause mortality: results from the Kawasaki Aging and Wellbeing Project

Abstract

Abstract Background: Increased protein intake has been recommended to prevent sarcopenia/frailty, but there are limited reports on the quantity and quality of protein intake needed and the associated prognosis, especially in much older individuals in Asia. In this study, we aimed to investigate the relationship between protein intake and prognosis in Japanese subjects, aged 85 years and older. Objectives: The data were obtained from The Kawasaki Aging and Wellbeing Project, which is a prospective cohort study of older adults aged between 85 and 89 with no physical disability at baseline. Of the 1026 adults in the cohort, 833 individuals were included in the analysis, excluding those who had not completed the brief self-administered diet history questionnaire or those who scored less than 24 on the Mini-Mental State Examination. The participants were grouped into quartiles based on protein intake: Q1 (protein < 14.7, %Energy), Q2 (14.7 ≤ protein < 16.7, %Energy), Q3 (16.7 ≤ protein < 19.1, %E), and Q4 (19.1 ≤, %Energy). Multivariate Cox proportional hazards models were utilized to evaluate the association between protein intake and all-cause mortality. Kaplan–Meier survival curves were employed to investigate the relationship between protein intake and mortality. Results: The mean protein intake of our study population was 17.0% of total energy. Animal protein intake, especially fish intake, increased significantly along with total protein intake. The study had an average observation period of 1,218 days and recorded 89 deaths. After adjusting for age, sex, skeletal muscle mass index, medical history, and education, a lower risk of all-cause mortality was observed in the group with the highest protein intake (Q4) than in the group with the lowest protein intake (Q1) (hazard ratio: 0.45, p-value: 0.017, 95% confidence interval: 0.22–0.93). This association between protein intake and prognosis remained robust even after adjusting for serum albumin and other nutrients, in addition to the aforementioned covariates. Conclusion: Protein intake is associated with a reduced risk of all-cause mortality in older adults aged ≥85 years who engage in independent activities of daily living. This association may impact prognosis via a mechanism that differs from muscle mass maintenance.