Our bodies hold onto fat stores when we're deficient in vitamin D, which we mainly get from sunlight, especially during the summer months.
Countering this deficiency seems to give the signal to the body to release stores of fat, as researchers from the University of Athens Medical School discovered when they gave supplements to a group of obese and overweight children and adolescents.
Around half the children were given vitamin D supplements—which they took every day for a year—and the rest were instead given a placebo, or dummy supplement.
By the end of the year, the supplement group had lost "significant" amounts of body fat, their BMI (body-mass index, a marker of obesity) had dropped, and their cholesterol levels had also improved.
Parents should ask to have the vitamin D levels of their overweight children checked, the researchers say.