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

Hyun Jung,Sukho Lee,Myong-Won Seo,Sung Kim,Jong Song

doi:10.3390/ijerph15092003

Abstract

Vitamin D insufficiency may be associated with increased risk of upper respiratory tract infection (URTI) in athletes. This study examined the effects of vitamin D3 supplementation on salivary immune functions and symptoms of URTI in vitamin D-insufficient taekwondo athletes. Twenty-five male taekwondo athletes, aged 19–22 years with vitamin D insufficiency [serum 25-hydroxyvitamin-D concentrations (25(OH)D, 31.3 ± 1.39 nmol/L)], participated in this study. They were randomized to receive 5000 IU/day of vitamin D3 (n = 13) or placebo capsule (n = 12) during 4 weeks of winter training. Blood samples were collected two times (pre- and post-tests) for analyzing serum 25(OH)D concentration while salivary samples were obtained three times (pre-, mid-, and post-tests) for secretory immunoglobulin A (SIgA) and lactoferrin analyses. The symptoms of URTI were reported daily during the intervention. Serum 25(OH)D concentration significantly increased by 255.6% in the vitamin D group, whereas in the placebo group it did not change (p < 0.001). While the significant increase in SIgA was observed in both groups (p < 0.001), elevated salivary lactoferrin level in response to winter training was found only in the placebo group (p = 0.011). The change in serum 25(OH)D concentration was negatively associated with total URTI symptoms (r = −0.435, p = 0.015). Vitamin D3 supplementation may be effective in reducing the symptoms of URTI during winter training in vitamin D-insufficient taekwondo athletes.

Highlights

Athletes of many sports participate in various training programs such as high-intensity interval training, strength training, and conditioning training to improve their athletic performance [1,2]. high-intensity training provides performance benefits, there is a physiological challenge to immune functions [3,4]
Vitamin D3 supplementation may be effective in reducing the symptoms of upper respiratory tract infection (URTI) during winter training in vitamin D-insufficient taekwondo athletes
There were no significant differences in body composition variables between the vitamin D and the placebo groups at baseline (p > 0.05)

Summary

Introduction

Athletes of many sports participate in various training programs such as high-intensity interval training, strength training, and conditioning training to improve their athletic performance [1,2]. High-intensity training provides performance benefits, there is a physiological challenge to immune functions [3,4]. It has been recognized that participating in moderate-intensity exercise comes with a lower risk of illness, whereas engaging in excessive volume of high-intensity exercise suppresses the immune functions, the risk of illness is increased. This concept has been introduced by Nieman known as ‘J-Curve’ [5]. Public Health 2018, 15, 2003; doi:10.3390/ijerph15092003 www.mdpi.com/journal/ijerph

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