Vitamin D supplementation in systemic lupus erythematosus: relationship to disease activity, fatigue and the interferon signature gene expression

Background In addition to the well-known role of vitamin D in calcium homeostasis and bone metabolism, vitamin D is important in the modulation of the immune system and inflammatory processes. Vitamin D deficiency is common in patients with systemic lupus erythematosus (SLE), possibly as a result of sun avoidance. The aim of this prospective open-label study was to assess the effect of the treatment of vitamin D deficiency and insufficiency in SLE patients, particularly with regards to disease activity, fatigue and interferon signature gene expression. Methods 31 SLE patients, 13 with vitamin D deficiency and 18 with vitamin D insufficiency were treated with vitamin D3. They were supplemented with vitamin D3 8000 IU daily for 8 weeks if they were vitamin D deficient, or 8000 IU daily for 4 weeks if they were insufficient. This was followed by 2000 IU daily maintenance. They were assessed at baseline, after 6 and 12 months by means of an interview, filling in questionnaires and blood tests. The expression of 12 interferon signature genes in RNA extracted from whole blood was measured by using QuantiGene Plex technology. Results An improvement in disease activity measured by systemic lupus erythematosus disease activity index-2K (SLEDAI-2K; p = 0.028) and fatigue measured by fatigue severity scale (FSS; p = 0.071) at 12 months were noted. A significant decrease in anti-double stranded deoxyribonucleic acid (dsDNA) titre (p = 0.045) was also noted. The mean interferon signature gene expression score decreased from baseline to 6 months, however statistical significance was not achieved (p = 0.165). Conclusions Improved disease activity and fatigue have been noted when Vitamin D has been supplemented in vitamin D deficient/insufficient SLE patients. One possible mechanism could be the suppression of the interferon signature gene expression. Trial registration: The study was registered with the ISRCTN registry on 12/04/2021 (Trial ID: ISRCTN59058825).