If young men who don’t have enough vitamin D take a high-dose vitamin D pill every day for 12 weeks while working out, they lose belly fat — but if they take a fake pill instead, their belly fat doesn’t change.

Taking a high-dose vitamin D pill every day for three months won't help young men who are low on vitamin D build more muscle or gain more lean body mass from weight training, even though their vitamin D levels go up to normal.

Taking a daily vitamin D pill of 8000 IU for 3 months can boost vitamin D levels in young men from dangerously low to healthy levels, while those who take a fake pill (placebo) stay low.

Taking a high-dose vitamin D pill every day for three months won't help young men who are low on vitamin D get stronger from weight training—and might even make them weaker compared to those who take a sugar pill.

If you're a young man with low vitamin D and you lift weights, your muscles will get stronger and you'll gain more muscle mass—even if you don't take vitamin D pills.

For older women who have trouble moving around and don’t have enough vitamin D, taking a daily vitamin D pill for four months might make their muscle fibers about 10% bigger than if they took a sugar pill — which could mean it helps build muscle.