You cannot smoke and sleep at the same time. This means that regular smokers, in effect, go through nightly nicotine withdrawal, which may contribute to a restless sleep and fatigue the next day.

According to a new study, smokers spend less time in deep sleep and more in light sleep than nonsmokers, with the greatest differences occurring in the early stages of sleep, according to an analysis of sleep EEGs.

Although the exact mechanism underlying these sleep disturbances in smokers is not known, withdrawal from nicotine is likely to be an important factor, says researcher Naresh M. Punjabi, M.D., Ph.D., of Johns Hopkins, co-author of this study, which appears in the February issue of Chest.

This study is unique, researchers said, because in addition to conventional sleep study methods, which rely heavily on self-reporting by subjects, they used a technique known as power spectral analysis of sleep EEG activity.

Not only is this method objective, but it can also detect extremely subtle changes in sleeping patterns.

The study included 40 smoker-nonsmoker pairs. They were matched for a list of factors, including age (mean age 56.8), gender (20 men in each group), race, body-mass index and other measures.

Spectral analysis of the sleep EEG showed that, compared with nonsmokers, smokers had a lower percentage of deep sleep, (59.7% versus 62.6%, respectively) and a higher percentage of light sleep, (15.6% versus 12.5%, respectively).

Smokers were also more likely to complain of a lack of restful sleep.

Although the exact mechanisms underlying the subjective and objective sleep disturbances in smokers need further study, nicotine is the prime suspect, the researchers said.