Vitamin D2 supplementation amplifies eccentric exercise-induced muscle damage in NASCAR pit crew athletes.
Level 2 - randomized trial
Randomized double-blind placebo-controlled trial
PubMed 24362707 · doi:10.3390/nu6010063
What was done
Twenty-eight NASCAR pit crew athletes were randomized in a double-blind design to receive either vitamin D2 (3,800 IU/day, n=13) or placebo (n=15) for six weeks. Baseline and post-supplementation muscle function were evaluated using leg-back and handgrip dynamometers, body weight bench press to exhaustion, vertical jump, and a 30-second Wingate test. Following the six-week intervention, participants performed a 90-minute eccentric exercise bout. Serum 25(OH)D2, 25(OH)D3, muscle damage biomarkers (myoglobin, creatine phosphokinase), and delayed onset muscle soreness (DOMS) were assessed immediately, 24 hours, and 48 hours post-exercise.
What was found
Six weeks of vitamin D2 supplementation increased serum 25(OH)D2 by 456% and decreased 25(OH)D3 by 21% relative to placebo (p < 0.001 and p = 0.036, respectively). Vitamin D2 had no effect on any muscle function test scores. Following eccentric exercise, the vitD2 group exhibited significantly higher muscle damage biomarkers than placebo: myoglobin increased 252% vs. 122% (p = 0.001), and creatine phosphokinase at 24 hours post-exercise rose 169% vs. 32% (p < 0.001). Ratings of DOMS did not differ between groups.
Why it matters
High-dose vitamin D2 supplementation may displace circulating 25(OH)D3 and exacerbate eccentric exercise-induced muscle damage in athletes without providing any measurable functional performance benefit.
Limits
The study had a small sample size (n=28) and was conducted exclusively in NASCAR pit crew athletes, limiting generalizability. It lacked a vitamin D3 comparison arm, and muscle damage was evaluated using systemic circulating biomarkers and subjective soreness ratings rather than direct tissue histology.
Cited by
- supports Preliminary studies indicate that vitamin D2 supplementation may inhibit some of the biological actions of vitamin D in skeletal muscle.