Neurodoc, you are right and thanks for correcting me on this. Apparently I am not the only one who thinks that cats synthesize Vitamin D with the help of sunlight, it’s all over the internet, cat books, etc. But I found this on a site that deals with animal nutrition:
“For most animals, vitamin D is a conditional nutrient in the diet in that it is only when that animal does not receive exposure to sunlight that it becomes an essential nutrient. Dr J.G. Morris recently demonstrated the inability of kittens to synthesize vitamin D when exposed to sunlight or UV light. The explanation is that the 7-dihydrocholesterol (the precursor for vitamin D synthesis) is in very low concentration in cat skin. In the wild state cats, obtain sufficient vitamin D from prey. Although we know now that vitamin D is an essential nutriment in cats, the dietary levels already recommended in commercial foods will fulfill all their requirements.”
It has nothing to do with being covered in fur, though.