Table 1. Dietary groups, serum calcium, and serum 1,25(OH)₂D₃ levels.

Diet		Serum biochemistry
Calcium, %	1,25(OH)2D3, ng/day	Calcium, mg/dl	1,25(OH)2D3, pg/ml
	Vitamin D-deficient group
0.02	0	5.5 ± 0.3	ND
	50	6.0 ± 0.2	169 ± 78
0.25	0	6.0 ± 0.1	ND
	50	12.6 ± 0.4*	68 ± 10
0.47	0	7.5 ± 0.3	ND
	50	11.2 ± 0.3*	151 ± 9
1.20	0	9.5 ± 0.2	ND
	50	15.8 ± 1.1*	72 ± 32
	Vitamin D-replete group
0.02	0	8.3 ± 0.1†	246 ± 39
	50	8.6 ± 0.1†	419 ± 56
0.25	0	8.6 ± 0.2	195 ± 40
	50	11.3 ± 0.2*	72 ± 11
0.47	0	8.9 ± 0.4	159 ± 16
	50	10.9 ± 0.1*	121 ± 24
1.20	0	9.2 ± 0.3	46 ± 8
	50	12.0 ± 0.2*	124 ± 22

Nonobese diabetic mice were fed a purified diet that contained 0.02%, 0.25%, 0.47%, or 1.20% calcium with or without 50 ng of 1,25(OH)₂D₃ per mouse per day. Study length was 3 weeks for vitamin D-deficient, calcium-restricted mice and 200 days for all other groups. Serum calcium was determined weekly by atomic absorption spectrometry (n = 4). At death, serum was collected and pooled, and the 1,25(OH)₂D₃ values were determined by a competitive binding assay (n = 2-4). All values are reported as the mean ± SEM. ND, not detectable. *, significance at P < 0.001 vs. 0 ng groups. †, significance at P < 0.001 vs. vitamin D-deficient, 0.02% calcium groups.