Vitamin D deficiency in connective tissue disease-associated interstitial lung disease.

OBJECTIVES: To determine and compare the prevalence of vitamin D deficiency in patients with connective tissue disease-associated interstitial lung disease (CTD-ILD).

METHODS: The level of vitamin D was determined by the serum levels of 1,25(OH)2D3. We evaluated 144 patients in our study, including 53 subjects in the CTD-ILD group and 91 subjects in the CTD group without ILD. CTD was diagnosed following the American College of Rheumatology criteria, and ILD was diagnosed by high-resolution computed tomography. Patients with other known causes of ILD and other pulmonary diseases were excluded. Vitamin D deficiency level was <20 ng/ml. This is a retrospective study.

RESULTS: Serum vitamin D levels were significantly lower in CTD-ILD patients (p<0.0001). Vitamin D deficiency was lower in the CTD-ILD group (mean±SD: 11.5±4.1 ng/ml) than in the control group (13.9±4.8 ng/ml, p=0.004). The CTD-ILD group was older (p=0.002), had higher levels of fibrinogen (p=0.028) and positive anti-CCP (p=0.026), faster ESR (p=0.001), lower serum levels of serum calcium (p=0.002), and more immunosuppressive therapies (p=0.011). Decreased serum albumin and higher positive antinuclear antibodies (ANA) were associated with reduced vitamin D levels in the vitamin D subgroups. When the odds ratio was adjusted for CTD-ILD, vitamin D deficiency was also a risk factor for CTD-ILD, whereas serum levels of calcium was a protective factor for CTD-ILD.

CONCLUSIONS: Serum vitamin D deficiency is associated with CTD-ILD and is a risk factor. Therefore, vitamin D may play a role in the pathogenesis of CTD-ILD.