Vitamin D

• Caffeine decreases vitamin D receptor protein expression. [1]
• Vitamin D might be good for muscles. [2][3]
• Vitamin D improves muscle strength and physical performance especially in elderly people. [3][4][5]

Reference

1. https://www.ncbi.nlm.nih.gov/pubmed/17223552
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901845/
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3513873/
4. https://www.ncbi.nlm.nih.gov/pubmed/18727936
5. https://www.ncbi.nlm.nih.gov/pubmed/26000306