There is a newly discovered downside to smoking: It leads to restless sleep. In a study of 40 healthy smokers and 40 non-smokers of similar age and weight, the two groups slept for the same amount of time, but smokers had higher levels of brain activity during sleep and reported feeling less rested during the day.

“In the absence of any other medical conditions, sleep is still impacted by smoking,” says Naresh M. Punjabi, associate professor of medicine and epidemiology at Johns Hopkins University. Nicotine may affect the sleep-wake cycle, causing stimulation early in the night (when levels of it are high) and mild withdrawal later (when levels are low), he says.

Poor sleep impairs mood, functioning, and health – and may make it harder for smokers to quit, he says. In fact, getting more sleep is associated with higher rates of smoking cessation, a different study has shown.

Punjabi says that future research could determine whether appropriately timing the delivery of nicotine-replacement therapy could improve quitters’ chances of success by preventing withdrawal and improving sleep quality. [source: Allure]