Vitamin D plays an essential role in bone mineralisation in particular by increasing the absorption of calcium. Diets usually contain little vitamin D (you can find vitamin D in fatty fish, liver, eggs, butter and cheese). Vitamin D is produced by the action of ultra violet light on your skin. Older people and children often have deficiencies in vitamin D. Dairy products fortified with vitamin D could be helpful for people at risk who are not taking supplements of vitamin D.