Do All Animals Receive Vitamin D From the Sun?

Fish don’t get vitamin D from the sun. Bottom-dwelling and deep sea fish have no need for synthesizing sunlight into vitamin D, because they are never exposed to the sun. While other fish benefit hugely from UV light and use plasma to process it, this is not where they get their vitamin D. Fish get vitamin D from food, such as plankton, and store it in their livers. Fish actually are a great source of dietary vitamin D for other animals.

Reptiles rely heavily on vitamin D. In fact, many reptiles simply cannot function without first basking in the sunlight to warm up and would die if prevented from seeing sunlight. However, inexperienced reptile keepers may inadvertently deny their pets vitamin D by not providing UV lamps. Mistakenly believing that their pets can get vitamin D when placed near a window, these pet owners simply are allowing their reptiles to warm up, as the vitamin D-containing UV cannot pass through glass or plastic.

Fur covering the skin of an animal, much like clothing covering the skin of a human, limits the amount of vitamin D absorbed from sunlight. A study on cows conducted at Aarhus University in Denmark found that cows with less fur coverage on the body had more vitamin D-producing plasma after exposure to the sun, suggesting that animals with fur-covered bodies were less capable and less likely to synthesize a sufficient amount of the vitamin from sun exposure.

Grass and hay is a good vitamin D source, but furry and feathered creatures have another way of getting their vitamin D. Although their coverage prevents them from absorbing the UV vitamin D directly, the act of grooming, namely the plucking of feathers and licking of fur, transfers small quantities of vitamin D stored externally into the digestive system, enabling the animals to process vitamin D internally.