In symptomatic OA (osteoarthritis) patients, foot pain is common. The deficiency of vitamin D is associated with chronic pain. The study exploring the effect of vitamin D depicted that in patients with symptomatic knee OA, vitamin D supplementation, and maintenance of sufficient vitamin D levels may alleviate foot pain for over two years.

The study aimed to investigate whether supplementation of vitamin D or maintaining sufficient vitamin D levels in patients with symptomatic knee OA diminishes foot pain.

The post hoc study from a randomized clinical trial named VIDEO (VItamin D Effect on Osteoarthritis) was conducted. The study recruited 413 knee OA patients with serum 25‐hydroxyvitamin D levels between 12.5-60 nmol/L. For two years, the participants were randomized to either monthly vitamin D3 (n=209) or placebo (n=204) group.

To assess foot pain, MFPDI (Manchester Foot Pain and Disability Index) was utilized. The Disabling foot pain was established when at least one of the 10 functional limitation items (items 1‐9,11) was recorded as on ‘most/every day(s)’ in the last month. To examine the change of MFPDI scores between groups, a repeated‐measure mixed-effect model was utilized.

The mean MFPDI score was found to be 22.8±7.3. At baseline, Disabling foot pain was present in 23.7% of patients. Over 2 years, considerable differences in MFPDI scores change between groups were witnessed, with more improvements in vitamin D group than in placebo group  and more improvement in those maintaining sufficient vitamin D levels (n=226) than those who did not (n=114) as shown in the following table and figures:

In knee OA patients, vitamin D supplementation may be beneficial for reducing foot pain.