Contribution of protein intake and its interaction with physical activity to transitions between disability states and to death in very old adults: the Newcastle 85+ Study

INTRODUCTION: Growth in the number of very old (≥ 85 years) adults will likely lead to increased prevalence of disability. Our aim was to determine the contribution of protein intake, and the interaction between protein intake and physical activity (PA), to the transition between disability states and to death in the very old using the Newcastle 85+ Study. METHODS: The analytic sample comprised of 717 older adults aged 85 years at baseline and living in the community. Protein intake was estimated with 2 × 24-h multiple pass recalls (24 h-MPR) at baseline. Disability was measured as difficulty performing 17 activities of daily living (ADL) at baseline, at 18, 36, and 60 months, and defined as having difficulties in one or more ADL. The contribution of protein intake [g/kg adjusted body weight/day (g/kg aBW/d)] to transition probabilities to and from disability, and to death over 5 years was examined by multi-state models adjusted for key health covariates. RESULTS: Participants were expected to spend 0.8 years (95% CI 0.6–1.0) disability-free and 2.8 years (95% CI 2.6–2.9) with disability between the ages 85 and 90 years. One unit increase in protein intake (g/kg aBW/d) halved the likelihood of incident disability (HR 0.44, 95% CI 0.24–0.83) but not for other transitions. Similar reductions in disability incidence were also found in individuals with protein intake ≥ 0.8 (HR 0.50, 95% CI 0.31–0.80) and ≥ 1 g/kg aBW/d (HR 0.49, 95% CI 0.33–0.73). Participants with high PA and protein intake ≥ 1 g/kg aBW/d were less likely to transition from disability-free to disability than those within the same PA level but with protein intake < 1 g/kg aBW/d (HR 0.45, 95% CI 0.28–0.72). CONCLUSION: Higher protein intake, especially in combination with higher physical activity, may delay the incidence of disability in very old adults. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00394-019-02041-1) contains supplementary material, which is available to authorized users.