A number of studies have indicated that many athletes are vitamin D deficient (optimal concentration is 30–60 ng/mL) yet there is an increasing evidence indicating a positive effect of vitamin D supplementation on physical performance. But the results from studies analysing the effect of supplementation on aerobic capacity reflected by maximum rate of oxygen consumption level (VO2max) are still ambiguous.
In the current study, researchers from Gdansk University, Poland, investigated the effects of eight weeks of a high dose of vitamin D3 supplementation and its impact on deficiencies and physical capacity.
The team studied 28 subjects, aged 19-22, who were divided into two groups: supplemented (SUP), who were given 6000 IU of vitamin D3 daily for eight weeks; and placebo group (PLA).
Serum 25-OH-D3 concentrations were determined in pre- and post-intervention and most were found to be deficient (20 ng/mL). The concentration significantly increased over time in the supplemented group, whilst it remained unchanged in the placebo group.
Moreover, the supplementation caused a significant improvement in maximal aerobic and anaerobic power whereas no changes were observed in the PLA group. The VO2max differences were also significant in the supplemented group.
The report concludes: "The current findings indicate that the improvement of aerobic and anaerobic capacity may be associated with vitamin D3 status. Moreover, eight weeks of vitamin D3 supplementation with a dose of 6000 IU per day significantly increases 25-OH-D3 serum concentration and was an efficient treatment of vitamin D3 deficiency among young healthy males."
Subjects from the supplemented group were given 6000 IU of vitamin D3 daily in capsule form (2000 IU per capsule), whereas the placebo group received identical-looking capsules containing sunflower oil. Capsules were administered in a single-blind design. All participants were asked to take three capsules per day in the morning for eight weeks.
The supplementation procedure was carried out from January to the beginning of March. The participants were medical university students (not professional athletes) and their physical activity level and diet were determined during the first interview.
One month before and during the experiment, participants did not take any vitamin or other supplements. The participants took part in three hours of supervised static cycling tests per week and diet did not differ from the accepted nutrition standards. Diets were not strictly standardised but the participants were instructed by the dietitian to maintain their nutritional habits throughout the whole experiment.
Aerobic (VO2max test) and anaerobic (Wingate Anaerobic Test) capacity were determined before and after the supplementation.