Taekwondo athletes helped by just 1 month of Vitamin D (longer would be better) - RCT May 2018

2 publications of the extremely short trial are on this page

Correcting Vitamin D Insufficiency Improves Some, But Not All Aspects of Physical Performance during Winter Training in Taekwondo Athletes.

Int J Sport Nutr Exerc Metab. 2018 May 3:1-25. doi: 10.1123/ijsnem.2017-0412. [Epub ahead of print]

PDF is available free at Sci-Hub   10.1123/ijsnem.2017-0412.

Jung HC1, Seo MW2, Lee S3, Jung SW2, Song JK2.
1 Department of Kinesiology, College of Health and Pharmaceutical Sciences, University of Louisiana at Monroe, Monroe, LA.
2 Department of Taekwondo, College of Physical Education, Global Campus, Kyung Hee University, Gyeonggi-do 17014, South Korea.
3 Department of Counseling, Health, and Kinesiology, College of Education and Human Development, Texas A&M University-San Antonio, San Antonio, TX.

We investigated the effects of vitamin D3 supplementation on physical performance during winter training in vitamin D insufficient taekwondo (TKD) athletes. Thirty-five collegiate male and female TKD athletes, aged 19-22 years with low serum 25(OH)D concentration (28.8±1.10 nmol/L) were randomly assigned to a vitamin D group (N=20) or a placebo group (N=15). Subjects received either a vitamin D3 capsule (5,000 IU/day) or placebo during four weeks of winter training. Blood samples were collected for analyzing serum 25(OH)D concentration. Physical performance tests included Wingate anaerobic test, isokinetic muscle strength and endurance, a counter movement jump (CMJ) test, sit-ups, agility test, and 20 m pacer. Serum 25(OH)D concentrations increased significantly in the vitamin D group (96.0±3.77 nmol/L) after four weeks of supplementation, but no changes were found in the placebo group (F=242.44, p=.000).
There were significant interaction effects for

• anaerobic peak power (F=7.49, p=.010) and
• isokinetic knee extension at 180°/sec (F=6.08, p=.019).

Changes in serum 25(OH)D concentration were positively associated with changes in peak power, and isokinetic knee extension at 180°/sec. However, no significant interaction effects were observed in other performance variables. This study suggests that four weeks of vitamin D supplementation elevates serum 25(OH)D concentration to sufficient levels. Correcting vitamin D insufficiency improves some, but not all aspects of performance. Thus, efficacy of vitamin D supplementation to enhance performance remains unclear.

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Vitamin D₃ Supplementation Reduces the Symptoms of Upper Respiratory Tract Infection during Winter Training in Vitamin D-Insufficient Taekwondo Athletes: A Randomized Controlled Trial - Sept 2018

Still not much results since the trial lasted only 1 month and they monitored the respiratory track problems from the first day, even though it would take 2-4 months to restore the levels of vitamin D
 Download the PDF from VitaminDWiki