Dairy free, Vegetarian Main uses: immune support, Crohn's disease, osteoporosis, coeliac disease (greater risk of osteoporosis), seasonal affective disorder. People who have little exposure to sunlight & vegans may choose to supplement their diets with this vitamin. Vitamin D increases absorption of calcium from food & reduces its excretion. It plays a role in insulin metabolism, blood cell formation & can be manufactured by the body on exposure to sunlight.