Eight-Week Vitamin D<sub>3</sub> Supplementation at 4000 IU/Day Was Not Associated with Further Improvements in Speed or Power Performance in Professional Female Soccer Players: A Randomized Controlled Trial.

Michalczyk MM, Gepfert M, Roczniok R, Zydek G. · Nutrients · 2026

Eighteen professional female soccer players took either 4000 IU/day of vitamin D3 or a placebo for eight weeks during preseason, with sprint, jump, blood, and vitamin D measures tracked. Most players already had sufficient vitamin D at the start, and supplementation produced no significant advantage over placebo in sprint times, jump performance, or blood markers, though sprint performance improved over time in both groups (likely from training).

Takeaway: Skip high-dose vitamin D as a performance booster if your levels are already sufficient, and test before supplementing.

Abstract (source)

Background: Vitamin D is involved in musculoskeletal function, but evidence that supplementation improves athletic performance remains inconsistent, particularly in athletes with sufficient baseline vitamin D status.

Methods: In this double-blind randomized controlled trial, 18 professional female soccer players were randomized during the autumn preparatory period (August-September) to receive vitamin D 3 (4000 IU/day; n = 9) or placebo ( n = 9) for eight weeks. Outcomes included total serum 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH) 2 D] concentrations, hematological variables, RAST total sprint time, 5- and 30-m sprint performance, and countermovement-jump outcomes.

Results: At baseline, after summer exposure, 25% of participants had insufficient or deficient 25(OH)D concentrations (≤30 ng/mL). The remaining cohort (75%) had sufficient 25(OH)D concentrations (>30 ng/mL). After eight weeks, no statistically significant between-group differences were observed in vitamin D metabolites, hematological variables, or performance outcomes (Δ25(OH)D: SG +12.4 ± 8.2 ng/mL vs. PG +3.1 ± 6.5 ng/mL; p = 0.12). RAST total sprint time ( p = 0.001) and 30-m sprint performance ( p = 0.005) improved over time.

Conclusions: Vitamin D 3 supplementation at 4000 IU/day for eight weeks was not associated with additional improvements in muscle strength, sprint performance, or countermovement-jump outcomes compared with placebo. Because most participants had sufficient baseline 25(OH)D concentrations, larger trials in female athletes with confirmed vitamin D insufficiency or deficiency are needed to determine whether individualized supplementation or longer intervention periods provide additional physiological or performance-related benefits. The trial was retrospectively registered at ClinicalTrials.gov (NCT07641075) on 8 June 2026.

Randomized controlled trialWomen's & Youth Athletics

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Eight-Week Vitamin D&lt;sub&gt;3&lt;/sub&gt; Supplementation at 4000 IU/Day Was Not Associated with Further Improvements in Speed or Power Performance in Professional Female Soccer Players: A Randomized Controlled Trial.

Related in Women's & Youth Athletics

Eight-Week Vitamin D<sub>3</sub> Supplementation at 4000 IU/Day Was Not Associated with Further Improvements in Speed or Power Performance in Professional Female Soccer Players: A Randomized Controlled Trial.