Effect of vitamin D₃ supplementation in winter on physical performance of university students: a one-month randomized controlled trial

Figures & data

Figure 1. Flow diagram of the study.

Among studied participants, 117 (93.6%) completed blood, vertical jump, hand grip, FVC, and FEV₁ analysis (vitamin D group n = 56 and control n = 61). At baseline, 104 participants completed VO₂max test.

Table 1. Baseline characteristics of the participants.

Variables	Vitamin D(n = 56)	Control(n = 61)
Age, year	19.0(19.0—20.0)	19.0(19.0—20.0)
Male, n (%)	39.0(69.6%)	40.0(65.6%)
Height, cm	173.36 ± 9.19	173.08 ± 9.66
Weight, kg	66.77 ± 14.46	68.53 ± 14.54
BMI, kg/m^2	22.01 ± 3.29	22.64 ± 3.01
Bone turnover
25(OH)D, ng/ml	18.85 ± 7.04	19.52 ± 8.65
N-MID, ng/ml	33.61 ± 13.96	30.58 ± 10.85
PTH, pg/ml	45.76 ± 18.65	50.92 ± 20.64
Calcium, mmol/L	2.37 ± 0.08	2.38 ± 0.08
Lipid profiles
TC, mmol/L	4.38 ± 0.74	4.45 ± 0.77
HDL-C, mmol/L	1.38 ± 0.31	1.37 ± 0.32
LDL-C, mmol/L	2.59 ± 0.67	2.58 ± 0.59
TG, mmol/L	0.91 ± 0.46	1.09 ± 0.74
FFA, mmol/L	0.39 ± 0.19	0.38 ± 0.17
Erythrocytes and hemoglobin-related parameters
Hb, g/L	152.80 ± 15.64	153.95 ± 14.41
HCT, %	46.23 ± 4.10	46.23 ± 3.67
RBC, 10^^12/L	5.05 ± 0.46	5.05 ± 0.40
RDW, %	40.98 ± 4.85	41.60 ± 2.27
Fatigue-related indicators
CK, U/L	276.18 ± 559.42	180.38 ± 121.51
LDH, U/L	187.80 ± 37.77	186.70 ± 30.95
T, ng/ml	4.29 ± 2.66	3.87 ± 2.40
Physical performance
VJH, cm	39.86 ± 9.84	37.44 ± 11.19
RHS, kg	413.13 ± 114.60	401.15 ± 111.30
FVC, L	4.33 ± 0.92	4.18 ± 1.04
FEV1, L	3.84 ± 0.77	3.78 ± 0.86
VO2max, ml/min	3181.86 ± 1139.70^a	3073.13 ± 1048.32^b
Physical activity level
Physical activity level, MET, h/day	1071.07 ± 255.16	1011.43 ± 242.25

Data are presented as mean ± SD or median (IQR) values for continuous variables and n (%) for categorical variables.

^an = 50. ^bn = 54.

Table 2. Changes of between baseline and follow-up in the intervention and the control group.

Variables	Vitamin D					Control					P value^d	P value^e
	Month 0		Month 1		Change^c	Month 0		Month 1		Change^c
	n	Mean ±SD	n	Mean ±SD	Mean ±SD	n	Mean ±SD	n	Mean ±SD	Mean ±SD
Weight and BMI
Weight, kg	56	66.77 ± 14.46	56	66.98 ± 14.63	0.21 ± 2.51	61	68.53 ± 14.54	61	68.44 ± 14.76	−0.09 ± 1.48	NS.	NS.
BMI, kg/m^2	56	22.01 ± 3.29	56	22.09 ± 3.41	0.08 ± 0.78	61	22.64 ± 3.01	61	22.60 ± 3.16	−0.03 ± 0.51	NS.	NS.
Bone turnover
25(OH)D, ng/ml	56	18.85 ± 7.04	56	26.98 ± 5.88	8.14 ± 3.85	61	19.52 ± 8.65	61	17.61 ± 8.19	−1.91 ± 2.58	0.000	0.000
N-MID, ng/ml	56	33.61 ± 13.96	56	32.05 ± 11.60	−1.57 ± 5.57	61	30.58 ± 10.85	61	30.64 ± 10.52	0.06 ± 6.31	NS.	NS.
PTH, pg/ml	56	45.76 ± 18.65	56	41.99 ± 20.92	−3.77 ± 15.71	61	50.92 ± 20.64	61	49.91 ± 19.52	−1.01 ± 23.20	0.043	NS.
Calcium, mmol/L	56	2.37 ± 0.08	56	2.37 ± 0.09	0 ± 0.11	61	2.38 ± 0.08	61	2.38 ± 0.08	−0.01 ± 0.1	NS.	NS.
Erythrocytes and hemoglobin-related parameters
Hb, g/L	56	152.80 ± 15.64	56	153.88 ± 15.29	1.07 ± 11.73	61	153.95 ± 14.41	61	153.15 ± 16.49	−0.8 ± 11.68	NS.	NS.
HCT, %	56	46.23 ± 4.10	56	46.56 ± 4.57	0.33 ± 3.25	61	46.23 ± 3.67	61	46.74 ± 4.56	0.51 ± 3.26	NS.	NS.
RBC,10^^12/L	56	5.05 ± 0.46	56	5.12 ± 0.48	0.07 ± 0.30	61	5.05 ± 0.40	61	5.14 ± 0.52	0.09 ± 0.30	NS.	NS.
RDW, %	56	40.98 ± 4.85	56	40.80 ± 3.48	−0.18 ± 5.42	61	41.60 ± 2.27	61	40.94 ± 3.64	−0.67 ± 3.21	NS.	NS.
Lipid metabolism
TC, mmol/L	56	4.38 ± 0.74	56	4.50 ± 0.86	0.13 ± 0.47	61	4.45 ± 0.77	61	4.68 ± 0.79	0.23 ± 0.45	NS.	NS.
HDL-C, mmol/L	56	1.38 ± 0.31	56	1.37 ± 0.29	−0.01 ± 0.17	61	1.37 ± 0.32	61	1.42 ± 0.31	0.05 ± 0.18	NS.	NS.
LDL-C, mmol/L	56	2.59 ± 0.67	56	2.71 ± 0.81	0.13 ± 0.43	61	2.58 ± 0.59	61	2.80 ± 0.67	0.22 ± 0.45	NS.	NS.
TG, mmol/L	56	0.91 ± 0.46	56	0.93 ± 0.39	0.02 ± 0.38	61	1.09 ± 0.74	61	1.03 ± 0.45	−0.06 ± 0.70	NS.	NS.
FFA, mmol/L	56	0.39 ± 0.19	56	0.44 ± 0.23	0.05 ± 0.26	61	0.38 ± 0.17	61	0.42 ± 0.27	0.05 ± 0.28	NS.	NS.
Fatigue-related indicators
CK, U/L	56	276.18 ± 559.42	56	184.05 ± 195.59	−92.13 ± 558.77	61	180.38 ± 121.51	61	154.79 ± 129.25	−25.59 ± 120.76	NS.	NS.
LDH, U/L	56	187.80 ± 37.77	56	173.91 ± 28.62	−13.89 ± 33.46	61	186.70 ± 30.95	61	171.44 ± 29.29	−15.26 ± 19.16	NS.	NS.
T, ng/ml	56	4.29 ± 2.66	56	4.26 ± 2.67	−0.03 ± 0.95	61	3.87 ± 2.40	61	3.85 ± 2.49	−0.01 ± 0.87	NS.	NS.
Physical performance
VJH, cm	56	39.86 ± 9.84	56	40.71 ± 10.39	0.85 ± 2.96	61	37.44 ± 11.19	61	37.82 ± 11.13	0.38 ± 3.21	NS.	NS.
RHS, kg	56	413.13 ± 114.60	56	416.07 ± 118.33	2.95 ± 27.99	61	401.15 ± 111.30	61	400.98 ± 114.26	−0.16 ± 29.72	NS.	NS.
FVC, L	56	4.33 ± 0.92	56	4.35 ± 0.98	0.02 ± 0.26	61	4.18 ± 1.04	61	4.17 ± 1.06	−0.01 ± 0.32	NS.	NS.
FEV1, L	56	3.84 ± 0.77	56	3.85 ± 0.81	0.01 ± 0.24	61	3.78 ± 0.86	61	3.77 ± 0.89	−0.01 ± 0.28	NS.	NS.

Month 0: measurements at baseline; Month 1: measurements after 1 month of intervention.

^cChange = Month 1 minus Month 0.

^dA repeated measure analysis of variance (ANCOVA) was used to evaluated the interaction effect for group by time.

^eBetween group differences were compared using the Mann–Whitney U-test.

NS: No significant.

Table 3. Association of subjects’ characteristics with 25(OH)D by multiple regression analyses at baseline and after 1 month of intervention (n = 117).

Variables	Month 0		Month 1
	ß (95% CI)	p-value	ß (95% CI)	p-value
Bone turnover
N-MID, ng/ml	−14.238 (−27.436 −1.041)	0.035	−0.132 (−0.338 − 0.074)	0.206
PTH, pg/ml	−24.866 (−49.424 −0.308)	0.047	−0.580 (−1.041 − 0.118)	0.014
Calcium, mmol/L	−0.0360 (−0.137 − 0.065)	0.484	−0.001 (−0.003 − 0.001)	0.271
Erythrocytes and hemoglobin-related parameters
Hb, g/L	−3.473 (−18.088 − 11.141)	0.639	−0.162 (−0.393 − 0.069)	0.166
HCT, %	−2.028 (−5.656 − 1.601)	0.271	−0.078 (−0.145 − 0.011)	0.022
RBC,10^^12/L	−0.326 (−0.703 − 0.051)	0.089	−0.009 (−0.016 − 0.002)	0.016
RDW, %	−1.906 (−6.504 − 2.692)	0.413	−0.001 (−0.078 − 0.075)	0.977
Lipid profiles
TC, mmol/L	−0.959 (−1.904 − −0.014)	0.047	−0.023 (−0.042 − −0.004)	0.016
HDL-C, mmol/L	−0.154 (−0.496 − 0.187)	0.372	−0.005 (−0.010 − 0.001)	0.121
LDL-C, mmol/L	−0.681 (−1.470 − 0.108)	0.090	−0.012 (−0.029 − 0.005)	0.151
TG, mmol/L	−0.27 (−1.040 − 0.500)	0.489	−0.013 (−0.022 − 0.004)	0.005
FFA, mmol/L	−0.255 (−0.479 − −0.030)	0.027	−0.001 (−0.007 − 0.004)	0.696
Physical performance
VJH, cm	11.473 (2.979 − 19.966)	0.009	0.245 (0.094 − 0.397)	0.002
RHS, kg	8.766 (−63.598 − 81.131)	0.811	0.787 (−0.525 − 2.100)	0.237
FVC, L	0.337 (−0.469 − 1.143)	0.410	0.014 (0.000 − 0.029)	0.052
FEV1, L	0.236 (−0.421 − 0.893)	0.479	0.007 (−0.005 − 0.019)	0.273

Statistically significant variables were adjusted for age, gender, and BMI; ß, unstandardized coefficient; 95%CI, confidence interval.

The 25(OH)D levels at baseline was log transformed for the analysis.

Table 4. Multiple linear regression analysis of VO₂max as the dependent variable (n = 104).

Prediction models	Coefficients	β	p-value	R^2	Adjusted R^2
Model 1				0.818	0.809
Athletic	−796.288	−0.367	.000
Gender	−386.803	−0.160	.025
Height, cm	34.228	0.286	.002
Weight, kg	15.992	0.213	.002
25(OH)D, ng/ml	678.148	0.099	.041
Model 2				0.830	0.820
Athletic	−744.219	−0.343	.000
Gender	−632.902	−0.262	.001
Height, cm	32.576	0.272	.002
Weight, kg	17.282	0.230	.001
25(OH)D, ng/ml	664.428	0.097	.039
Hb, g/L	−11.065	−0.141	.011
Model 3				0.840	0.825
Athletic	−726.065	−0.335	.000
Gender	−638.730	−0.264	.005
Height, cm	28.210	0.235	.009
Weight, kg	15.884	0.211	.008
25(OH)D, ng/ml	667.603	0.097	.036
Hb, g/L	−9.158	−0.117	.040
RHS, kg	−0.398	−0.039	.628
FVC, L	405.912	0.356	.028
FEV1, L	−355.659	−0.258	.115

B, unstandardized regression coefficients; β, standardized regression coefficients.

The 25(OH)D levels was log transformed for the analysis.

Athletic (athletes = 1, non-athletes = 2); Gender (Man = 1, Woman = 2).

Model 2: as in model 1 plus Hb.

Model 3: as in model 2 plus RHS、FVC、FEV₁.

VO₂max(ml/min) = −726.065 × Athletic − 638.730 × Gender + 28.210 × Height + 15.884 × Weight + 667.603 × 25(OH)D −9.158 × Hb + 405.912 × FVC.

Data availability statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.