[Effect of vitamin D supplementation and outdoor time on the 25(OH)D level in adolescents].

OBJECTIVE

To assess the effect of vitamin D( VD) supplementation and outdoor time intervention on the 25( OH) D level in adolescents.

METHODS

In April2015, participants from three classes in a college of North Anhui were randomly assigned to VD supplementation group( receive oral vitamin D3 of 800 IU/d for 4 weeks, n = 55), outdoor time intervention group( more than 30 min/d of outdoor between 9 am and 15 pm for 4 weeks, n = 52) and control group( no any intervention, n = 63). The data on demographic characteristics, behavior related to vitamin D and life style were evaluated by using questionnaire. 25( OH) D level in finger-tip blood was measured by using LC-MS/MS. The differences of 25( OH) D levels among 3 groups over 4 weeks were compared.

RESULTS

On baseline, there was no significant difference( F = 0. 77, P = 0. 464) on the25( OH) D level among VD supplementation group( 15. 5 nmol/L, 95% CI 14. 3- 16. 6nmol/L), outdoor time intervention group( 16. 5nmol/L, 95% CI 15. 2- 17. 8 nmol/L)and control group( 16. 0 nmol/L, 95% CI 14. 9- 17. 1 nmol/L). However, the 25( OH)D level of VD supplementation group( 56. nmol/L, 95% CI 52. 0- 61. 6 nmol/L) and outdoor time intervention group( 54. 3 nmol/L, 95% CI 49. 4- 59. 3 nmol/L) were significantly higher( F = 4. 40, P = 0. 014) than that of the control group( 47. 2 nmol/L, 95% CI 42. 7- 51. 7 nmol/L) 4 weeks later. All participants among 3 group were all in VD deficiency( < 50 nmol/L) on baseline. After 4 weeks, the prevalence of VD deficiency among 3 group reduced to 40. 0%( 95% CI 27. 7%- 53. 2%), 48. 1%( 95%CI 34. 8%- 61. 5%) and 65. 1%( 95% CI 52. 9%- 76. 1%), respectively. Compared with the control, the risk of VD deficiency in VD supplementation group significantly decreased( RRadj= 0. 33, 95% CI 0. 15- 0. 72, P = 0. 005), and the risk in the outdoor time intervention group also obviously decreased( RRadj= 0. 48, 95% CI 0. 22- 1. 05, P = 0. 065), but did not reach statistical significance.

CONCLUSION

The 25( OH) D level of adolescents could be significantly improved through oral vitamin D3 supplementation of800 IU/d or more than 30 min/d of outdoor.