The Study
Does vitamin-D intake during resistance training improve the skeletal muscle hypertrophic and strength response in young and elderly men? – a randomized controlled trial
This study is like a fair test where some guys got extra vitamin-D and others didn’t, and then they all did leg workouts. The results show that vitamin-D didn’t make their legs stronger or bigger, but it might have changed some tiny parts inside the muscles — so we can say vitamin-D is linked to those changes, but we can’t say it caused them.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Taking extra vitamin D while doing leg workouts didn't make muscles bigger or stronger overall, but it helped older men get more strength from each unit of muscle, and helped younger men shift their muscle fibers to a more powerful type.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 553 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — even without bigger muscles, improved muscle quality means older adults can move more efficiently, reducing fall risk; younger men may build more powerful muscle fibers faster.
- 2Young men: 3% more type IIa fibers (p=0.030), 6% less myostatin mRNA (p=0.006).
- 3Elderly men: 8% higher strength per muscle area (p=0.008).
- 4No change in muscle size or total strength with vitamin D.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Nutrition & Metabolism
Year
2015
Authors
J. Agergaard, J. Trøstrup, J. Uth, J. V. Iversen, A. Boesen, J. Andersen, P. Schjerling, H. Langberg
Related Content
Claims (6)
Taking a lot of vitamin D might help your muscles grow bigger by turning down a natural brake that stops them from growing.
When older men lift weights for 12 weeks and take a daily vitamin D3 pill, their muscles get stronger relative to their size compared to men who only take calcium — even though their muscles don’t get bigger or stronger in absolute terms.
Taking a daily vitamin D3 supplement while doing strength training might help young men build more of a certain type of muscle fiber and reduce a protein that limits muscle growth, compared to just taking calcium.
Doing strength training for 12 weeks can make your thigh muscles bigger and stronger, whether you're young or old—but taking vitamin D pills won’t make that improvement any better.
Taking vitamin D pills while doing weight training doesn’t change the levels of a specific protein in your muscles that helps vitamin D work, which means vitamin D probably isn’t helping your muscles grow by using this protein.
When older men take vitamin D pills while doing weight training, their bodies might slow down the production of a specific enzyme because they have too much vitamin D in their blood — like a safety switch turning itself off.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.