Dr. Susan Y. Chon of the University of Texas M.D. Anderson Cancer Center says there's no safe amount of time people can stay in the sun without increasing skin cancer risks.
"Some people may absorb enough vitamin D from their routine outdoor exposure," Chon says in a statement. "However, the benefits of UV exposure may be limited because they can lead to increased risks of developing skin cancer."
On a hot summer day, unprotected skin can be damaged in as little as 15 minutes, Chon says.
To avoid skin cancer, Chon recommends getting vitamin D from food and, if necessary, supplements.
"Most people can get their daily fill of vitamin D by drinking a cup of milk and eating a 3-ounce serving of salmon, Chon says.
Other foods high in vitamin D:
-- One tablespoon of cod liver oil offers 1,360 IUs.
-- One serving (about 3 ounces) of certain fish provides a healthy dose of vitamin D -- salmon provides 447 IUs per serving, mackerel provides 388 IUs per serving, and tuna provides 154 IUs per serving.
-- One cup of whole, reduced fat or non-fat milk is fortified with vitamin D and provides 115-124 IUs of vitamin D.
-- Fortified ready-to-eat cereals provide at least 40 IUs per serving.