In a break from past presidential campaigns, neither U.S. Sen. Barack Obama, D-Ill., nor Sen. John McCain, R-Ariz., is willing to release their medical records, making a true assessment of their health nearly impossible, presidential health expert Dr. Lawrence Altman wrote Monday in The New York Times.

"There may be no serious problems with the health of any of the nominees. But absent fuller disclosure, there is no way for the electorate to know," Altman wrote.

Atman said even though McCain, 72, released nearly 1,200 pages of medical information in May, the documents were restricted and inconsistencies within them left unanswered questions about his melanoma cancer.

Obama, 47, has an admitted problem with smoking and is chewing nicotine gum to control it. But the only medical information his campaign had released until last week was a one-page, undated letter from his personal physician stating that Obama was in "excellent" health.

Since then, standard lab tests from checkups in 2001, 2004 and 2007 have been released, with the findings normal, the Times said.