Circannual Vitamin D Serum Levels and Disease Activity in Rheumatoid Arthritis: Northern Versus Southern Europe

Background: Greater intake of vitamin D has been associated with a lower risk of rheumatoid arthritis (RA) and low serum vitamin D together with higher prevalence of RA seem common among North European people when compared to Southern Europe.

Objectives: To evaluate serum 25-hydroxyvitamin D [25(OH)D] levels in female RA patients from North (Estonia) and South (Italy) Europe and to correlate them with the disease activity score (DAS28) during winter and summer.

Methods: Fifty-four RA Italian patients (IP) and 64 RA Estonian patients (EP) were evaluated for serum 25(OH)D levels in winter and summer time, as well as for DAS28 score. Normal female controls (C) were 35 (IC) and 30 (EC) age-matched subjects, respectively. 25(OH)D concentrations were measured by a competitive radioimmunoassay. Statistical analysis was performed by "r" Pearson correlation, "t" Student with Bonferroni correction and by repeated ANOVA measures (summer and winter) with two factors (country and clinical status).

Results: 25(OH)D levels were found significantly higher in IP versus EP (p = 0.0116) both in winter and in summer time. Differences were observed also in controls. The variations (increase) of 25(OH)D levels between winter and summer were found significant (p = 0.0005) in both IP and EP. Differences were observed also in controls. No significant differences were found concerning 25(OH)D levels between RA patients and their controls in either country. Interestingly, a significant negative correlation between 25(OH)D and DAS28, was found in summer only in IP (r =-0.57, p < 0.0001) and in winter in EP (r =-0.40, p < 0.05).

Conclusion: Significantly lower 25(OH)D serum levels were observed in RA patients from North versus South Europe with a circannual rhythm in winter and summer time. In addition, 25(OH)D values showed a significant correlation (negative) with RA clinical status (DAS28) in both North and South European RA patients, suggesting possible effects of vitamin D among other factors on disease activity.