Association of protein intake per kilogram body weight with decline in activities of daily living and death in the older Japanese population: NIPPON DATA90

BackgroundThe aging population in Japan highlights the public health need to maintain functional abilities, with activities of daily living (ADL) being essential for healthy aging.AimWe prospectively examined the association between protein intake (g/BWkg/day) and the ADL decline or death risk among older Japanese adults.MethodsData from 1773 Japanese adults aged ≥65 years in the NIPPON DATA90 cohort were analyzed. Protein intake was assessed using data from the 1990 National Nutrition Survey of Japan, and individual intakes were estimated from household dietary records. Protein intake (g/BWkg/day) was categorized into sex-specific quartiles. ADL decline was defined as requiring assistance in ≥1 of ADL tasks during follow-up surveys (1995-2012). Logistic regression was used to estimate odds ratios for ADL decline or death by survey year, and Cox proportional hazards models examined hazard ratios for time-to-event ADL decline or death.SummaryDuring follow-up, 515 participants experienced ADL decline, and 1015 died. Among women, moderate protein intake (second quartile, 1.15-1.38 g/BWkg/day) was associated with a 35% lower risk of ADL decline (adjusted hazard ratio 0.65) compared with the lowest quartile. A similar pattern was observed for the combined outcome of ADL decline or death, whereas higher intake levels did not show additional benefit. No clear association was observed among men. These findings suggest that moderate protein intake was associated with the lowest risks of ADL decline and death, particularly among women. Adequate, but not excessive, protein consumption may help support functional health in older Japanese adults.