Differences in exercise might partly explain the gap, he suggested. One of the study's authors, Jim Smith, said the English exercise somewhat more than Americans. But physical activity differences won't fully explain the study's results, he added.

Marmot offered a different explanation for the gap: Americans' financial insecurity. Improvements in household income have eluded all but the top fifth of Americans since the mid-1970s. Meanwhile, the English saw their incomes improve, he said.

Robert Blendon, a professor of health policy at the Harvard School of Public Health who was not involved in the study, said the stress of striving for the American dream may account for Americans' lousy health.

"The opportunity to go both up and down the socioeconomic scale in America may create stress," Blendon said. Americans don't have a reliable government safety net like the English enjoy, Blendon said.

However, Britain's universal health-care system shouldn't get credit for better health, Marmot and Blendon agreed.

Both said it might explain better health for low-income citizens, but can't account for better health of Britain's more affluent residents.

Marmot cautioned against looking for explanations in the two countries' health-care systems.

"It's not just how we treat people when they get ill, but why they get ill in the first place," Marmot said.