Background In patients with knee osteoarthritis (OA) muscle weakness is common and is strongly related to more pain and activity limitations. Therefore, conservative treatment focuses on optimizing muscle strength in patients with knee OA. Determinants of muscle strength such as muscle quantity and quality, level of pain and physical activity are widely studied in knee OA. Only a limited number of studies have focused on the relation between nutrition and muscle strength in patients knee OA.

Protein is an essential building block for muscle tissue. Adequate dietary protein intake is needed to preserve muscle tissue. In a part of the general older population lower intakes than the recommended daily protein intake are observed ^1,2. Higher levels of dietary protein intake have been linked to greater muscle mass and strength in older adults^3,4. Whether there is an independent association between lower dietary protein intake and lower muscle strength in knee OA patients in unknown.

Objectives To determine whether lower dietary protein intake is associated with lower muscle strength in patients with knee OA.

Methods In this cross-sectional study, baseline data of patients with symptomatic and radiographic knee OA from the progression subcohort of the Osteoarthritis Initiative (OAI) were used. Protein intake was measured by the Block Brief 2000 food frequency questionnaire and expressed as g per day/ kg bodyweight. Knee muscle strength was measured in the index knee by the Good Strength chair test, and expressed as the sum of both flexion and extension strength (N/kg bodyweight). Linear regression analysis was used to test the association, adjusting for relevant demographic, clinical and behavioral confounders.

Results Data from 1128 patients (mean age 61.7±SD 9.1 y., 60.4% female) were used. A Kellgren and Lawrence grade of 2, 3 or 4 was scored in 25.7%, 44.7% and 30.0% of the patients, respectively.The mean daily protein intake was 0.68±SD 0.26 g/kg bodyweight, and the mean muscle strength was 5.33±SD 1.96 N/ kg bodyweight. In the unadjusted model, lower protein intake was associated with lower muscle strength (B = -0.804, 95% CI -0.336 to -1.272, p=0.001). After adjusting for age and gender, lower protein intake was still associated with lower muscle strength (B = -1.102, 95% CI -0.680 to -1.524, p<0.001) and was maintained after controlling for other relevant confounders.

Conclusions Lower protein intake is independently associated with lower muscle strength in patients with knee OA. To confirm this relationship, future research is needed to test this association in longitudinal and interventional studies in patients with knee OA.

References

1. Fulgoni VL, 2008, Am J Clin Nutr 87:1554S–1557S.

2. Kerstetter et al., 2003 J Nutr 133:855S–861S.

3. Houston et al., 2008 Am J Clin Nutr. 2008 Jan; 87(1):150–5.

4. Beasley et al., 2013 J Am Geriatr Soc. 2013;61(11):1863–71.

References

Disclosure of Interest None declared