Michele Stanten explains the connection between vitamin D and weight loss in her new book Walk Off the Weight:
Extra body fat holds on to vitamin D so that the body can't use it. This perceived deficiency interferes with the action of the hormone leptin, whose job is to tell your brain that you're full. And if you can't recognize when you're satiated, you're more likely to overeat.
Current recommendations for daily intake of the vitamin, also known as the sunshine vitamin since the body synthesizes it from contact with the sun's rays, is 200 IU, but many health practitioners think the amount should be upped to 1,000 IU daily. Obtaining sufficient vitamin D from natural food sources alone can be challenging, so taking a supplement if you're falling short is a good idea. And don't skip the egg yolks either! There's about 17 IU of vitamin D in one egg yolk.