Background Muscle weakness is frequent in patients with knee osteoarthritis (OA) and is an important contributor to pain and activity limitations1. Determinants of muscle weakness in knee OA include pain, disuse, aging and low-grade inflammation. In addition, vitamin D deficiency, which is common in older adults, has been linked to muscle weakness since low serum 25-hydroxy (OH) vitamin D level has been found to be related to impaired muscle cell function2. In knee OA, the association between serum 25(OH) vitamin D level and muscle strength has not been studied profoundly.
Objectives To assess the association between serum 25(OH) vitamin D level and muscle strength in patients with knee OA.
Methods Baseline data from 297 patients (105 men and 193 women with a mean age of 60.6±8.2 years) with knee OA from the Amsterdam Osteoarthritis (AMS-OA) cohort were used. Muscle strength (in N/kg) of the upper leg (flexion and extension) was measured with an isokinetic dynamometer. In blood serum, 25(OH) vitamin D level (in nmol/L) was measured. Uni- and multivariable linear regression analyses were used to analyze the association between 25(OH) vitamin D level and muscle strength. Confounders that were considered relevant included age, gender, body mass index (BMI), season of blood collection (summer/winter), erythrocyte sedimentation rate value, C-reactive protein value and WOMAC-physical functioning subscale.
Results Lower level of 25(OH) vitamin D was associated with lower muscle strength (B=0.003, 95%CI 0.001 to 0.005, p<0.001). The association was not significant when BMI was incorporated in the model (B=0.001, 95%CI -.001 to 0.003, p=0.254).
Conclusions Low 25(OH) vitamin D level and muscle weakness are associated. BMI affects this association strongly. Further studies are needed explaining the associations between vitamin D, fat metabolism and muscle strength in knee osteoarthritis.
Holla JF, van der Leeden M, Peter WF, Roorda LD, van der Esch M, Lems WF, Gerritsen M, Voorneman RE, Steultjens MP, Dekker J. Proprioception, laxity, muscle strength and activity limitations in early symptomatic knee osteoarthritis: results from the CHECK cohort. J Rehabil Med. 2012 Oct;44(10):862-8.
Wicherts IS, van Schoor NM, Boeke AJ, Visser M, Deeg DJ, Smit J, Knol DL, Lips P. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrinol Metab 2007;92:2058-65.
Disclosure of Interest None declared
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