Vertebrates, including humans, need vitamin D for healthy bones. Humans must expose their skin to sunlight to synthesise certain types of vitamin D – if we are completely covered up with clothing, we risk not synthesising enough.
But many vertebrates are covered in fur, wool or feathers, reducing their skin’s exposure to sunlight.
Some carnivores, including domestic dogs and cats, get most of their vitamin D through their diet. Other animals have an oily coating on their fur, wool or feathers, and this oil, when in contact with sunlight, makes vitamin D.
And ring-tailed lemurs, are known to ‘sunbathe’, exposing the undersides of their limbs.
While it has been suggested (and is a popularly-held belief) that these animals obtain vitamin D by grooming themselves and ingesting the oil, research on sheep, cows and birds indicates that they actually get the vast majority of their vitamin D by just standing in sunlight.
The external oil is not an important source of the vitamin.
So, it seems that a coat of wool, fur and feathers does not block sunlight in the same way that human clothes do, and that many animals manage to get a good dose of vitamin D by simply hanging out in the sunshine.
