Seems like there is always more good news about Vitamin D. This time it's a study that finds supplementation with Vitamin D combined with resistance training in overweight people led to a smaller waist than a placebo control group. 

The body can make Vitamin D when exposed to sunlight, but during the winter, especially in the northern latitudes it's very unlikely you're getting enough.

Vitamin D is also beneficial for bone health, immune system support, asthma symptoms, and weight loss. You can read the study here - 

Impact of vitamin D supplementation during a resistance training intervention on body composition, muscle function, and glucose tolerance in overweight and obese adults