We’ve made statements supporting keeping cats indoors in different posts, and on our Cats fact sheets in the Resources section. There were many reasons for this, including keeping your cat safe from predators and other cats, and reducing the risk of infectious disease exposure. Outdoor cats are much more likely to pick up various infectious diseases, some of which can be harmful to the cat and some of which can be spread to people. This is a particular concern in households with people that are at increased risk of infection or where infections might result in more serious disease (i.e infants, elderly, people with compromised immune systems, pregnant women).
Recently, a comment was submitted in response to one of those posts. It questioned whether indoor cats would get enough vitamin D. It’s a logical question and a good example of the differences between animal species. In people and some animal species, sunlight (UV light) exposure is important for production of vitamin D. Vitamin D is an essential vitamin and numerous health problems have been associated with vitamin D deficiency. However, cats are very poor at producing vitamin D in response to sunlight exposure. They get their vitamin D from their food. In the wild, cats get it from the prey they hunt. Pet cats get it from good quality pet foods that are supplemented with vitamin D.
Cats do not benefit from sunlight, from a vitamin D standpoint, so concerns over vitamin D should not be a factor in deciding whether your cat goes outside or not.