When you have more vitamin D in your body, your fat cells send out more of a signal called leptin, which tells your brain you’re full and don’t need to store more fat—so you might gain less fat over time.

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.

In men who carry extra fat around their belly, when their vitamin D levels go up or down, their leptin levels (a hormone that affects hunger) also change — even when you account for how much fat they have in different parts of their body.

Having more vitamin D in your body might help you build more muscle and store less fat, directing your body’s energy toward making lean tissue instead.

If overweight men lose a lot of belly fat over a year by eating better and moving more, their hunger hormone (leptin) goes down and their vitamin D levels go up — both by about a quarter.

When overweight men lose body fat through lifestyle changes like diet and exercise over a year, their vitamin D levels go up by about 27% and their leptin (a hunger hormone) levels drop by 27%—and these two changes seem to be connected, even after accounting for how much fat they lost in different parts of their body.