Vitamin D is commonly lauded for its role in bone health and good moods, but new study suggests that it may also have a role in metabolism and weight loss. In one prior study, for example, when vitamin-D-deficient women increased their blood levels of vitamin D to recommended levels, they lost more weight. According to the National Institutes of Health, potential symptoms of vitamin D insufficiency include bone pain and muscular weakness. Even if you take vitamin D pills, don't assume that your levels are enough. When the women in the research took supplements, they absorbed varying levels of the vitamin.