Effect Of Vitamin D Supplementation And Outdoor Activity On The 25(OH)D Level In Adolescents

Objective: Vitamin D deficiency has become the global public health problem.Vitamin D not only has important influence on calcium-phosphorus metabolism and skeletal muscle health but also has comprehensive effect on other tissue cells of the body.Furthermore,recent researches show that vitamin D deficiency is closely related to many kinds of diseases.This dissertation takes adolescents as participants,intervenes in vitamin D supplementation and outdoor activity time among them,explores the difference of the effects of the above two intervention methods on the 25(OH)D level,evaluates vitamin D deficiency among adolescents and provides some useful guidelines for adolescents to supply vitamin D appropriately.Methods: In April 2015,participants from three class in a college of North Anhui were randomly assigned to vitamin D supplementation group(receive oral vitamin D3 of 800 IU/D for 4 weeks,n=55),outdoor activity intervention group(more than 30 min/d of outdoor activities 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 droped to Whatman 903 and measured by using LC-MS/MS.The differences of 25(OH)D levels among 3 groups over 4 weeks were compared.Chi-square test was used to compare the difference of basic characteristics and outdoor activity time among the aforementioned three groups,ANOVA was used to analyze the changes of the 25(OH)D level between before and after intervention among the three groups,and multi-factor logistic regression was used to investigate the effects of two intervention methods on vitamin D deficiency.Results: There was no difference in Confounding factors among three groups.There was no significant difference on valid outdoor activity time among the three groups(?2=4.32,P=0.115)before intervention.But the valid outdoor activity time of outdoor activity intervention group was significantly higher than that of vitamin D supplementation group and the control group 4 weeks later(?2=28.07,P<0.001).There was no significant difference on the 25(OH)D level among the three groups(15.5nmol/L,16.5nmol/L and 16.0nmol/L;F=0.77,P=0.464)before intervention.However,the 25(OH)D level of VD supplementation group(56.8±4.8nmol/L)and outdoor activity intervention group(54.3±4.9nmol/L)were significantly higher(F=4.40,P=0.014)than that of the control group(47.2±4.5nmol/L)4 weeks later.All participants among the three groups were all in vitamin D deficiency(< 50 nmol/L)on baseline.After 4 weeks,the prevalence of vitamin D deficiency among 3 group reduced to 40.0%,48.1% and 65.1%,respectively.Compared with the control,the risk of vitamin D deficiency in vitamin D supplementation group significantly decreased(RRadj =0.33,95% CI: 0.15-0.72,P=0.005),and the risk in the outdoor activity intervention group also obviously decreased(RRadj =0.48,95%CI:0.22-1.05,P=0.065),but did not reach statistical significance.Conclusions: The situation of vitamin D deficiency among the adolescents is serious.The 25(OH)D level of adolescents could be significantly improved through oral vitamin D3 supplementation of 800 IU/D or more than 30 min/d of outdoor activities.That is to say,to supply vitamin D3 can decrease vitamin D deficiency significantly in the short run.However,given that nearly half of the participant were in vitamin D deficiency after intervention,the dose of 800IU/D was not enough to reverse the vitamin D deficiency.