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.

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.

Taking a lot of vitamin D might help your muscles grow bigger by turning down a natural brake that stops them from growing.

Taking vitamin D might help your body release a hormone that tells you when you're full and also stop a protein that blocks muscle growth, so you could feel more energized and build muscle more easily.

When mice can't use vitamin D properly, their muscles get weaker, their muscle fibers shrink, and a protein that stops muscle growth increases—so vitamin D seems to help keep muscles strong and healthy.

When scientists remove the vitamin D receptor in mice, the genes that help muscles grow and repair don't work right anymore, which might mess up how their muscles heal or develop.