Background Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease in which fatigue and impaired quality of life (QoL) commonly manifest. Fatigue has been associated with increased disease activity in SLE1-3 and both fatigue and disease activity are considered predictors of impaired QoL2-4, although some studies have not reported any association between disease activity and QoL5-6.
Objectives The aim of this study was twofold, firstly to determine whether vitamin D is associated with fatigue and QoL in SLE patients during the winter when status would be expected to be lowest and again during summer when vitamin D levels are thought to be highest and secondly to examine for any relationship between fatigue, QoL and disease activity.
Methods SLE patients were recruited from November to March (winter) (n=52) and followed up during June and July (summer) (n=50). Serum 25-hydroxyvitamin D (25(OH)D) was measured by liquid chromatography mass spectrometry. Fatigue was assessed using the fatigue severity score (FSS) and QoL was examined using the 36-item short form questionnaire (SF-36). Disease activity and damage were scored using versions of Systemic Lupus Activity Measure, Systemic Lupus Erythematosus Disease Activity Index, British Isles Lupus Assessment Group and Systemic Lupus International Collaborative Clinics/American College of Rheumatology. Primary statistical analysis included Spearman’s rho correlation and two tailed paired t-test. Multivariate and logistic regression analysis was employed to investigate potential predictors of fatigue and QoL. To investigate whether vitamin D was associated with fatigue and QoL, data from the serial winter and summer measurements were combined to give a larger sample (n=102) with greater power and regression analysis was reapplied.
Results During the winter and summer months respectively 47 (96%) and 49 (98%) SLE patients reported fatigue (FSS ≥ 3) and 98% of the cohort presented with vitamin D inadequacy (25(OH)D < 75 nmol/L) throughout the year. The mental component score (MCS) (95% CI 0.02, 5.42, P=0.049) and social functioning (SF) (95% CI 1.01, 13.27 P=0.023) subscales of the SF-36 were reduced during the summer. Analysis from the serial winter and summer data, reported vitamin D status to be reduced in those with fatigue (n=96) (95% CI -39.46, -2.03, P=0.030) and FSS and SF-36 significantly correlated with all disease activity measures.
Conclusions Vitamin D inadequacy, fatigue and poor QoL were prevalent in this cohort of Northern Irish SLE patients. Given the observation of reduced vitamin D in those with fatigue and the association between vitamin D and disease activity, it is plausible that improvements in fatigue mediated via increasing 25(OH)D may indirectly improve disease activity and possibly enhance QoL. Further research such as placebo controlled vitamin D intervention trials are warranted to investigate this hypothesis before any firm conclusions can be made.
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Disclosure of Interest None Declared