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.

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.

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.

If a man with excess belly fat eats less and moves more for a year, his belly fat, hunger hormone levels, and vitamin D levels all get better.

Men who had excess belly fat saw their vitamin D levels go up by 27% after a year of eating better and moving more—even though they didn’t take any vitamin D pills or supplements.

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.