Protein intake and muscle strength in older persons: Does inflammation matter?

Objectives To examine whether protein intake is associated with change in muscle strength in older persons. Because systemic inflammation has been associated with protein catabolism, the study also evaluated whether a synergistic effect exists between protein intake and inflammatory markers on change in muscle strength. Design Longitudinal. Setting The Invecchiare in Chianti Study. Participants Five hundred and ninety-eight older adults. Measurements Knee extension strength was measured at baseline (1998-2000) and during 3-year follow-up (2001-2003) using a handheld dynamometer. Protein intake was assessed using a detailed food frequency questionnaire. The inflammatory markers examined were C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Results The main effect of protein intake on change in muscle strength was not significant. However, a significant interaction was found between protein intake and CRP (P =.003), IL-6 (P =.049), and TNF-α (P =.02), indicating that lower protein intake was associated with greater decline in muscle strength in persons with high levels of inflammatory markers. Conclusion Lower protein intake was associated with decline in muscle strength in persons with high levels of inflammatory markers. These results may help to understand the factors contributing to decline in muscle strength with aging and to identify the target population of older persons who may benefit from nutritional interventions aimed at preventing or reducing age-associated muscle impairments and its detrimental consequences.