The Study
Overexpression of the vitamin D receptor (VDR) induces skeletal muscle hypertrophy
This study found that people who got bigger muscles from lifting weights also had more of a protein called VDR in their muscles — but that doesn’t mean VDR made them bigger. It’s like noticing people who eat more ice cream also have more sunburns — they’re linked, but ice cream doesn’t cause sunburn.
Analysis score
Maximum 72 for a cohort study.
Where the score came from
Scientists made a special muscle switch (VDR) work harder in rats and their muscles grew bigger. In people who lifted weights for 20 weeks, those whose muscles made more of this switch also gained more muscle mass — even if their vitamin D levels didn’t change.
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 544 / 100
Quality score
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — a 17% muscle fiber increase in rats is large and likely meaningful; in humans, VDR as a biomarker could help predict who gains muscle best from training.
- 2Rats: 17% bigger muscle fibers.
- 3Humans: VDR levels went up with muscle gain, but not with strength or vitamin D in blood.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Molecular Metabolism
Year
2020
Authors
J. Bass, Asif Nakhuda, C. Deane, M. Brook, D. Wilkinson, B. Phillips, A. Philp, J. Tarum, F. Kadi, D. Andersen, A. M. Garcia, Ken Smith, I. Gallagher, N. Szewczyk, M. Cleasby, P. Atherton
Related Content
Claims (6)
When scientists turned up the vitamin D receptor in the leg muscles of rats for 10 days, the muscle fibers got bigger, the muscles made more protein, and key growth signals kicked in—so it looks like boosting this receptor might help muscles grow.
When people do supervised weight training for 20 weeks, their muscles make more of a protein called VDR—and that’s linked to gaining more muscle mass, but not to getting stronger or having more vitamin D in their blood. So VDR might be a sign that muscle growth is happening, even if vitamin D levels don’t change.
In rats, having more of a protein called VDR seems to help muscle repair cells multiply and grow, while reducing a protein that stops muscle growth—so it might help rats build more muscle.
In rats, having more of a protein called VDR seems to turn on genes that help build stronger muscle scaffolding, which might help the muscles grow bigger and work better.
When people lift weights, their muscles seem to adjust how they use vitamin D internally, and that change matches up with how much of a certain enzyme they make in the muscle — but it doesn’t match up with how much vitamin D is floating in their blood. So maybe what’s happening inside the muscle matters more than what’s in the bloodstream.
If you make muscle cells produce more of a protein called the vitamin D receptor, the muscles get bigger because they start making more protein, grow more repair cells, and stop a protein that normally limits muscle growth.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.