Smoking Tied to Memory Loss in Middle Age

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But one expert said he wasn't convinced that the study had proven a connection between smoking and memory loss.

"There are two things that are a little concerning about the [study] results that would give us pause before definitely concluding that smoking leads to a decrease in memory," said Dr. Michael Siegel, a professor of social and behavioral sciences at Boston University.

First, the results for smoking as a cause of memory loss were only significant when other health factors weren't taken into account, Siegel noted. "That suggests that smoking is associated with other types of health behaviors that are affecting the outcome," he said. "When other health behaviors were included, it completely wiped out the effect of smoking."

And second, Spiegel said he wasn't sure why ex-smokers performed better on the memory tests. "The reason their memory is better is not because they smoked -- that's not plausible," he said.

Smoking may not be the reason for memory impairment, Siegel said. Rather it may be that people who never smoked or quit smoking have better overall health habits, may be better educated, and may have a higher level of cognitive functioning to begin with, he said.

Dr. Norman H. Edelman, scientific consultant to the American Lung Association, said: "This study is generally a confirmation of previous work. But there is a fundamental question: Are they stupid because they smoke or do they smoke because they are stupid?"

More information

For more on quitting smoking, visit the American Lung Association.