Association between low 25-hydroxyvitamin D, insulin resistance and arterial stiffness in nondiabetic women with systemic lupus erythematosus

Objective: The objective of this paper is to examine if there is an association between low levels of 25-hydroxyvitamin D (25(OH)D) and insulin resistance (IR) in nondiabetic women with systemic lupus erythematosus (SLE) and to evaluate its impact on arterial stiffness.

Patients and methods: In this cross-sectional study 25(OH)D, insulin, insulin resistance measured by the homeostatic model assessment (HOMA-IR), homocysteine, fibrinogen, characteristics of SLE, medications and pulse-wave velocity (PWV) were measured in 106 nondiabetic women with SLE and 101 matched controls.

Results: Women with SLE tended to have lower 25(OH)D levels (p = 0.078) and a higher frequency of 25(OH)D deficiency (defined as < 10 ng/ml) than controls (p = 0.058). Patients from the lowest quartile of the 25(OH)D range had higher PWV (p = 0.043), fasting glucose (p = 0.035), insulinemia (p ≤ 0.001), HOMA-IR (p = 0.006), C4 (p = 0.012), as well as more frequent IR (p = 0.002) and metabolic syndrome (p = 0.052) than those in the upper quartile, and no differences were found in age, body mass index (BMI), blood pressure, lipid levels and renal function. In women with SLE, 25(OH)D inversely correlated with insulin (p = 0.006), HOMA-IR (p = 0.008) and C4 (p = 0.048) and tended to correlate with fibrinogen (p = 0.060) after adjustment for BMI, age, SLEDAI, prednisone dose, renal function, inflammation markers and seasonal variation, but not with PWV. In controls, 25(OH)D correlated only with homocysteine after the same adjustment, and the correlation with PWV tended to be significant after adjustment for BMI and age (r = -0.190, p = 0.10).

Conclusion: Low 25(OH)D levels were found to be associated with increased IR in nondiabetic women with SLE independently of BMI. Low 25(OH)D levels, but not IR, could be associated with increased arterial stiffness in these patients.