Vitamin D Deficiency Associated With Increased Osteoarthritis Symptoms and Reduced Pain Threshold

HONOLULU, HI—Study investigators presented data from the UPLOAD (Understanding Pain & Limitations in OsteoArthritic Disease) study at the American Pain Society's 31^st Annual Scientific Meeting demonstrating that hydroxyvitamin D levels <25ng/mL were associated with an increase in osteoarthritis (OA) symptoms and a decreased threshold for pressure pain.

A clinically meaningful threshold value associating vitamin D levels and chronic pain outcomes has yet to be determined. Experts conservatively suggest that hydroxyvitamin D levels <10ng/mL denote severe deficiency, 10–19ng/mL indicate moderate insufficiency, and 20–29ng/mL signify mild insufficiency. Toni Glover, MSN, ARNP, FNP-BC, from the University of Florida, Gainesville, FL, and colleagues conducted a study to determine a clinically useful vitamin D threshold level that would be predictive of individuals' reported chronic pain-related symptoms and response to evoked experimental pain.

A total of 155 patients with chronic knee pain, regardless of radiographic evidence of OA were recruited. Patient demographics were 73% female, mean age of 56 years, and racially diverse (48% African Americans/Blacks and 52% Whites). Upon radiographic exam of the knees, 67% of participants had Kellgren-Lawrence OA scores from 2–4 (mild to severe). Total serum vitamin D was obtained by high performance liquid chromatography (total 25-hydroxyvitamin D= 25(OH)D2 + 25(OH)D3). Of the patients, 73% had vitamin D levels <30ng/mL and 9% had severe deficiency at <10ng/mL.  Vitamin D supplementation of <1000 IU/day was taken by 28%, 20% supplemented with >1000 IU/day, and 52% did not supplement.

Patients completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and underwent pressure algometry at the knee to determine thresholds for pressure pain (PPT). Compared with vitamin D levels ≥25ng/mL, patients with vitamin D levels <25ng/mL had significantly increased WOMAC total scores (F_1,90=5.46, P=0.02) and diminished PPT (F_1,90=11.54, P =0.001), indicating greater self-reported OA symptoms including pain, stiffness, physical dysfunction and increased pain sensitivity to mechanical stimulation, respectively.

Using the Short Performance Physical Battery (SPPB), patients were evaluated on their ability to perform balance tests, stand up from sitting in a chair, and walk a 4-meter timed course. There were non-significant main effects of vitamin D level <25ng/mL and BMI >30 on SPPB score, however, there was a significant interaction effect (P<0.01). Thus, investigators stated, if the vitamin D level was <25ng/mL and the BMI was >30, patients had worse lower extremity function as measured by SPPB.

These findings demonstrate that low levels of vitamin D are associated with chronic knee pain and that levels <25ng/mL may be used as a clinical threshold to treat vitamin D insufficiency with the goal of mitigating chronic pain, concluded Dr. Glover.