Vitamin D also plays a critical role in building and protecting your bones. Vitamin D promotes calcium absorption, and studies show that people with low levels of vitamin D have lower bone density or bone mass. They are also more likely to break bones as they age. Vitamin D is naturally present in very few foods, but you can get it from sunshine, and more foods are being fortified with this very important nutrient. While cod liver oil is perhaps the best natural food source of Vitamin D, there are other, better-tasting options.