Low protein intake, muscle strength and physical performance in the very old: The Newcastle 85+ Study

Background: Low protein intake has been linked to reduced muscle strength and physical performance in older adults but little is known about how it may affect muscle health and subsequent functional decline in the very old (aged 85+), who are at enhanced risk of malnutrition and loss of muscle mass and strength. Aims: To investigate the associations between low protein intake, defined as the intake of <1 g protein/kg adjusted body weight/day (<1 g/kg aBW/d) and decline in muscle strength and physical performance in the very old. Methods: The analytic sample consisted of 722 community-dwelling participants (60% women) from the Newcastle 85+ Study who had protein intake at baseline. Participants were followed-up for change in grip strength (GS) and Timed Up-and-Go (TUG) test over 5 years (baseline, 18, 36, and 60 months). We used mixed models to determine the effects of low protein intake on muscle strength and physical performance in all participants, and also stratified by sex. Results: At baseline, 390 (54%) participants (261 women, p < 0.001) reported low protein intake, and these differed from participants with good intake (≥1 g/kg aBW/d) on several measures of health and function. In the model adjusted for protein intake, consuming <1 g/kg aBW/d of protein was associated with a 1.62 kg lower GS (p = 0.008) in all participants, and especially in women (β (SE) = −0.83 (0.41), p = 0.05) after adjusting for key baseline covariates (anthropometry, multimorbidity, arthritis in hands, cognitive status and physical activity). The rate of decline in GS over 5 years was not associated with protein intake. Women, but not men, with low protein intake had worse baseline TUG (β (SE) = 0.04 (0.02), p = 0.03) compared with those with good protein intake in the fully adjusted model, but the rate of decline in TUG was not affected by daily protein status. Conclusions: Intake of <1 g protein/kg aBW/d may negatively affect muscle strength and physical performance in late life, especially in older women, independently of important covariates. More research is needed in the very old to define the optimal protein intake for maintenance of muscle health and function.