Women who wish to maximize their success in quitting smoking should time their quit date to when they are in the latter phase of their menstrual cycle, a new study shows.

Cigarette smoking remains the leading cause of preventable death in the U.S. and women experience more severe health consequences from it, including a 25 percent higher risk of coronary heart disease and chronic obstructive pulmonary disease (COPD). Women also have greater difficulty with quitting than do men, studies find.

In a previous study, University of Pennsylvania research had shown women who are in the follicular phase of menstruation, which is early in the menstrual cycle, have greater responses to smoking cues in reward-related brain regions when compared to when they are in the later part of their cycle. It is during this later phase, when their progesterone-to-estrogen ratio is high, that they are less likely to give into addictive behaviors, the researchers have found.

They took 38 healthy, premenopausal female smokers, ages 21 to 51, and gave them a functional MRI scan to examine how regions of the brain that help control behavior are functionally connected to regions of the brain that signal reward.

The women in the study were separated into two groups – those in their follicular phase (earlier) of their cycles and those in their luteal, or later phase. The results revealed that during the earlier phase, there was reduced functional connectivity between brain regions that helps make good decisions (cortical control regions) and the brain regions that contain the reward center (ventral striatum), which could place women in greater risk for continued smoking and relapse, the researchers say.

The study shows that women who time their quit date towards the latter part of their cycle, when their progesterone-to-estrogen ratio is higher, may be better protected against the impulse to quit, the researchers said of their findings, which appear in Biology of Sex Differences, and was also presented at the annual meeting of the Organization for the Study of Sex Differences (OSSD).