Influence of Vitamin D Status on Fatigue in Ankylosing Spondylitis

Abstract

Fatigue is a common symptom in ankylosing spondylitis. Hypovitaminosis D is one of the factors influencing fatigue during inflammatory rheumatisms. This study aimed to determine the influence of vitamin D deficiency on fatigue in ankylosing spondylitis. In this cross-sectional study, 40 patients with ankylosing spondylitis and 40 patients suffering from low back pain were recruited. Clinical and laboratory data, including vitamin D dosage, disease activity, functional impairment, and quality of life, were evaluated using specific and validated scores. Fatigue was assessed by the FACIT-F score. Both groups of patients were compound of 27 men and 13 women with a mean of 43.55±12.26 years in the study group and 47.77±13.63 years in the case group, respectively. Ankylosing spondylitis was active according to the ASDAS_CRP score in 67.5% of cases. All patients were suffering from fatigue with a mean FACIT-F score of 21.13. Severe levels of fatigue were noted in 50% of cases. 92.5% of patients were vitamin D deficient with a mean vitamin D of 16.57±7.15 ng/mL. Factors associated with fatigue were: female gender (P=0.05), spinal pain (P<0.001), enthesitis (P<0.001), disease activity (P<0.001), functional impairment (P<0.001), and quality of life (P<0.001). However, smoking was the only factor related to vitamin D deficiency (P=0.05). Vitamin D level was not correlated with fatigue (r= -0.02, P=0.91). In our study, vitamin D status did not seem to have an impact on fatigue in patients with ankylosing spondylitis.