title: Vitamin D supplementation reduces insulin resistance in Japanese adults: a secondary analysis of a double-blind, randomized, placebo-controlled trial.
abstract: Higher circulating 25-hydroxyvitamin D (25[OH]D) concentration has been linked to a lower prevalence of insulin resistance and type 2 diabetes mellitus. However, randomized controlled trials have not clarified the effect of vitamin D supplementation on insulin resistance in healthy adults. The objective of this study was to assess the effect of vitamin D supplementation for 1 year on insulin resistance; the study was a secondary analysis of a clinical trial. We hypothesized that increased 25(OH)D concentration after vitamin D supplementation for 1 year would significantly improve insulin resistance. Ninety-six healthy adults participated in this study, of whom 81 completed the study. The participants randomly received daily either 420 IU vitamin D3or placebo in a double-blind manner for 1 year. The levels of fasting insulin, glucose, and other parameters were assessed at baseline and after 1 year of intervention. Homeostasis model assessment of insulin resistance index was calculated from insulin and glucose levels. Visceral fat area and physical activity were also investigated. Serum 25(OH)D and 1,25-dihydroxyvitamin D concentrations were significantly increased by approximately 29.5 nmol/L and 7.0 pg/mL, respectively, after 1-year vitamin D supplementation. After vitamin D supplementation, fasting glucose levels and values of homeostasis model assessment of insulin resistance index significantly decreased from 88.3 to 85.3 mg/dL (P < .01) and 1.17 to 0.84 (P < .01), respectively, and the results were independent of physical activity and visceral fat accumulation. In conclusion, the present study showed that vitamin D supplementation for 1 year effectively improves fasting glucose level and insulin resistance in healthy Japanese adults.
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192, Japan.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Sun
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192, Japan; Key Laboratory of Exercise and Health Sciences of Ministry of Education, School of Kinesiology, Shanghai University of Sport, 399 Chang Hai Rd, Shanghai 200438, China. Electronic address: caozb_edu@yahoo.co.jp.
authors.forename: Zhen-Bo
authors.initials: ZB
authors.lastname: Cao
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192, Japan.
authors.forename: Kumpei
authors.initials: K
authors.lastname: Tanisawa
authors.affiliation: Graduate School of Sport Sciences, Waseda University, Tokorozawa, Saitama 359-1192, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ito
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Oshima
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, 359-1192, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Higuchi
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D002762:Cholecalciferol / Q000097:blood / Q000494:pharmacology* / Q000627:therapeutic use; D019587:Dietary Supplements; D004311:Double-Blind Method; D005215:Fasting; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood*; D007333:Insulin Resistance; D007564:Japan; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D001786:Blood Glucose; D007328:Insulin; D014807:Vitamin D; D002762:Cholecalciferol; C097949:1,25-dihydroxyvitamin D; C104450:25-hydroxyvitamin D
keywords: 25(OH)D; Insulin resistance; Percent body fat; Physical activity; Visceral fat area