The question came up after new warnings against tobacco from the surgeon general.
Gibbs said the president has been chewing nicotine gum to help break his smoking habit.
"He understands its dangers and, I think, has done a lot of extraordinary work to wrestle with that habit as millions of Americans have," Gibbs said.
About 46 million adults, or one in five, still smoke. Millions more are regularly exposed to other people's fumes.
The Associated Press contributed to this report.