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Table 1 Characteristics of the included randomized controlled trials

From: Effects of vitamin D3 supplementation on serum 25(OH)D concentration and strength in athletes: a systematic review and meta-analysis of randomized controlled trials

ReferenceCountryLatitudeSeasonSports ActivityRandomized (n = 163)Intervention Vitamin D Dosage IU (μg)DurationTypeProduct
Jung 2018 [30]Korea33.3° NWinterTaekwondo22/2250004 weeksD3 capsulesBio-Tech Pharmacal, Inc. (Arkansas, USA)
Fairbairn 2018 [31]New Zealand45–46.5° SAutumnRugby28/293570 IU (89 μg)/day11–12 weeksD3 tabletsCal.D.Forte, PSM Healthcare, Auckland, New Zealand
Close 2013b [32]UK53° NWinterSoccer5/55000(125)/day vs. PL8 weeksD3 capsulesBiotech Pharmacal Inc., Phoenix, AZ, USA
Close 2013a [28]UK53° NWinterFootball and Rugby10/10/1020,000 (500)/week vs. 40,000 (1000)/week vs. PL12 weeksD3 capsulesBiotech Pharmacal Inc., Phoenix, AZ, USA
Wyon 2016 [29]UK52.3° NWinterJudo11/11150,000 (3750)/one time vs. PL8 daysD3 tabletsNot reported
  1. Data are means unless stated otherwise; PL Placebo. 2013a, 30 football and rugby athletes were recruited in reference 28; 2013b, 10 soccer players were recruited in reference [32]