In contrast to vitamin D from sunlight, dietary vitamin D is available during any season and offers a reliable source of the vitamin for individuals who do not have access to sunlight
exposure. Oily fish is the most important dietary source of vitamin D [1], whereas most other foods from animal origin contain very low amounts and do not significantly contribute to
an improvement of vitamin D status. A recent study was able to ascertain UVB exposure of hens as a highly effective approach to increase the vitamin D content in eggs [2]. Data from that study
showed that UVB radiation increased the vitamin D content much stronger than feeding the maximum permissible dosages of dietary vitamin D3.