Impact of vitamin D deficiency on efficiency of rehabilitation programs in patients with ankylosing spondylitis

Low blood vitamin D concentrations are associated with incidence, risk of development, activity and more severe clinical course of ankylosing spondylitis (AS). 58 patients with AS (males 62.1%, age 48 (39-58) years) were examined to study the impact of vitamin D deficiency on the efficiency of rehabilitation measures under the programs of sanatorium and resort therapy. Determination (25-OH) of vitamin D level, haematological indices SII (systemic immune-inflammation index; SII = number of platelets × number of neutrophils/number of lymphocytes) and SIRI (systemic inflammation response index; SIRI = number of neutrophils × number of monocytes/number of lymphocytes) were performed on admission to the sanatorium and before discharge. The average BASDAI disease activity index was 3.0 (2.4-3.5) points. Low AS activity was documented in 31% and moderate activity, in 69% of patients. The baseline vitamin D levels showed negative correlation with pain intensity score (VAS, visual analog score) during walking (ρ = -0.44, p 0.001). Association of these measures at discharge persisted but was less significant (ρ = -0.27, p = 0.039). In the total group of AS patients, vitamin D deficiency ( 20 ng/mL) was observed in 13.8%, and mild deficiency levels (ranging from 20 to 29 ng/mL) have been revealed in 25.9% of cases. When comparing patients with normal ( 30 ng/mL) and reduced (≤ 29 ng/mL) vitamin D levels, significant differences were noted for VAS (p = 0.0025), ESR (p = 0.040) and SIRI (p = 0.046). All patients with AS were divided into two groups: Group I (n = 26) admitted for treatment from regions with low level of solar insolation; Group II (n = 32) arrived for treatment from regions with high insolation levels. Initially, a significantly lower vitamin D content was observed in AS patients in group I (p = 0.040). A three-week stay and treatment at the sanatorium (an area with high solar insolation) was associated with an increase in vitamin D levels (p = 0.027), and decreased VAS pain intensity (p = 0.017) only in group II patients. When testing the inflammatory markers, only SIRI showed a significant decrease in group II patients with AS in the course of treatment (p = 0.038). In conclusion, the hematological SIRI index objectively reflects clinical dynamics of AS patients arriving for sanatorium and resort therapy from the regions with different levels of solar insolation.