The measured free 25(OH)D correlated markedly with 25(OH)D3 (r = 0.92, p < 0.05) and serum albumin (r = −0.4, p < 0.05) in the control group; in the diabetes group, there was no such relationship (r = 0.42 and 0, respectively, p > 0.05). Here, ALB is linked to diabetes mellitus.