A recent 2013 study demonstrtared tthat patients with severe OSAS had significantly lower levels of 25(OH)D as compared with mild (50 patients), moderate (50 patients) and severe OSAS (50 patients) . Also, the number of patients with serum 25(OH)D deficiency (<10 μg/dl) were higher in OSAS group than in controls. Researchers concluded that when the severity of OSAS increases, 25(OH)D deficiency becomes more pronounced.