Vitamin D does not occur naturally in any fruit. It is a fat-soluble vitamin found naturally in oily fish, beef liver, cheese, some mushrooms and egg yolks. Milk, orange juice and breakfast cereals are often fortified with vitamin D, and the vitamin is also available as a supplement.
Humans can synthesize vitamin D through exposure to the ultraviolet-B wavelengths found in sunlight but need at least 5 to 30 minutes of sun exposure to the face, arms, legs or back twice a week to maintain adequate levels. Cloud cover and shade reduce UVB exposure by 50 to 60 percent, and window glass and sunscreens with a sun protection factor of eight or more block it completely.
In children, vitamin D deficiency can cause rickets, a disorder in which the bones do not mineralize properly. Its clinical signs are soft bones and bone deformities. Dark-skinned infants who are breast-fed for prolonged periods without receiving vitamin D supplements are the most vulnerable. In adults, vitamin D deficiency can cause osteomalacia, or weakening of the bones, and it is associated with bone pain and muscle weakness. There is also increasing evidence suggesting that maintaining an adequate level of vitamin D is important in preventing cancers of the colon, prostate and breast.