Table 2.

Comparison of serum vitamin D levels and other blood parameters between night-shift workers and daytime workers.

Characteristics	Daytime Workers (n = 432)	Night-Shift Workers (n = 412)	P
25-hydroxyvitamin D, ng/mL
Crude model	14.95 ± 8.37	13.22 ± 5.79	< .001
Adjusted model	14.25 ± .36	13.96 ± .37	.597
Blood parameters
Calcium, mg/dL	9.41 ± .34	9.27 ± .34	< .001
Phosphate, mg/dL	3.79 ± .54	4.00 ± .65	< .001
Creatinine, mg/dL	0.68 ± .12	0.65 ± .10	.001
Blood urea nitrogen, mg/dL	12.46 ± 3.29	12.32 ± 2.82	.511
Alanine transaminase, IU/L	18.88 ± 13.47	16.57 ± 11.29	< .001
Aspartate aminotransferase, IU/L	22.17 ± 7.29	20.42 ± 5.46	.007
Alkaline phosphatase, IU/L	57.92 ± 17.69	53.37 ± 13.07	< .001
Total bilirubin, mg/dL	0.62 ± .22	0.64 ± .28	.247
Gamma glutamyl transpeptidase, IU/L	18.76 ± 17.73	14.50 ± 9.40	< .001
Season of blood test, n (%)			< .001
Spring and winter (December to May)	247 (57.2)	300 (72.8)
Summer and autumn (June to November)	185 (42.8)	112 (27.2)
Vitamin D supplement use, n (%)	25 (5.8)	11 (2.7)	.025
Vitamin D deficiency, n (%)	146 (33.8)	133 (32.3)	.661

Data are presented as mean ± standard deviation (SD) for numerical data and number (percentage) for categorized data. Crude model: data are presented as mean ± SD. Independent t test was performed. Adjusted model: data are presented as adjusted means ± standard error. Analysis of covariance was performed after controlling for age, sex, season of blood test, serum levels of calcium, phosphate, creatinine, blood urea nitrogen, alanine transaminase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, and gamma glutamyl transpeptidase.