Relationship between vitamin D and osteoarthritis

Background. Osteoarthritis (OA) is a common joint disease and one of the leading causes of disability worldwide. The role of vitamin D in the etiology and development of OA is still unclear, but it may be important for both diagnosis and timely therapy.

Aim. To evaluate the relationship of vitamin D levels with clinical and instrumental parameters in OA in a cross-sectional study.

Materials and methods. The study included 171 patients aged 40–75 with confirmed knee OA according to the American College of Rheumatology (ACR) classification, stage I–III (according to Kellgren and Lawrence). All patients signed informed consent. The mean age was 53.5±9.94 years, body mass index (BMI) was 29.8±6.4 kg/m², and disease duration was 3 [1; 7] years. For each patient, a case record form was filled out, including anthropometric indicators, medical history, clinical examination data, an assessment of knee joint pain according to the Visual Analog Scale (VAS), WOMAC, and the patient's general health condition (PGHC). All patients underwent standard radiography, knee ultrasound examination and magnetic resonance imaging (MRI) (WORMS), densitometry of the lumbar spine and femoral neck, and laboratory tests. Statistical processing of the data was performed using the Statistica 10 software.

Results. Normal vitamin D values (≥30 ng/mL) were found in 62 (36.3%) patients, low levels (<30 ng/mL) in 109 (63.7%) patients, insufficiency (<30 ng/mL and >20 ng/mL) in 66 (38.6%) patients, and deficiency (<20 ng/mL) in 43 (25.1%). Patients were divided into three groups according to the presence or absence of vitamin D insufficiency/deficiency: Group 1 included patients with normal vitamin D levels, Group 2 included patients with insufficiency, and Group 3 included patients with vitamin D deficiency. Patients of the three groups were comparable in age and disease duration but differed significantly in body weight, BMI, and waist measurement (higher in groups with reduced vitamin D values; p<0.05). Also, these patients had significantly higher VAS pain scores, total WOMAC and its components (pain, stiffness, and dysfunction), PGHC, and worse KOOS. More patients in Groups 2 and 3 had OA of the hip and hand joints, clinically detected synovitis, flat feet, and quadriceps muscle hypotrophy. Ultrasound examination significantly more often revealed a reduction of cartilage tissue on both the anteromedial and anterolateral surfaces of the knee joint; MRI showed more often osteitis in the medial condyles of the femur and tibia (p<0.05 for all values).

Conclusion. Our study demonstrated that low blood vitamin D levels (insufficiency/deficiency) were associated with a more severe knee OA. These patients had a large body weight, BMI, higher VAS pain values, WOMAC index (overall and its components), worse KOOS, PGHC, and smaller cartilage sizes in the medial parts of the knee joint (according to ultrasound); such patients were significantly more likely to have osteitis in the medial parts of the femur and tibia according to MRI. Also, stage II and III knee OA and OA of other localizations, clinically detected synovitis, quadriceps hypotrophy, and flat feet were more common.