January might seem like the ideal time to ditch an unhealthy habit. After all, everybody's doing it! (Or at least claiming they are.)
However, a new study suggests that trying to change your behavior at the wrong point in your menstrual cycle could thwart your good intentions—regardless of the calendar year.
In the study, researchers set out to determine whether hormone fluctuations enhance the desire to smoke, which could, in theory, make it more difficult to quit. To find out, they showed 15 male and 19 female smokers images designed to induce cigarette cravings, then used magnetic resonance imaging (MRI) to monitor participants' brain responses. Researchers tested each woman on two different occasions (once at the beginning of her cycle, and once about two weeks later) and measured hormone levels each time.
While the tempting images induced cravings in both men and women, they really activated the brain areas related to cravings in women right before and right after they got their periods.
Researchers think this could be due to a dip in estrogen and progesterone. It's a hormonal shift that's linked to moodiness and anxiety, which could make you more susceptible to temptations that provide a mood-boosting reward and more likely to give in because of preexisting notions about PMS (i.e., that it triggers chocolate cravings), says study author Adrianna Mendrek, Ph.D., an associate psychology at Bishop's University in Quebe
Either way, "the neurobiological mechanism underlying cravings are very similar when it comes to drugs of abuse or natural rewards, such as food," she adds. In other words, these hormonal fluctuations can mess with your resolve and make you less likely to stick to your guns, whether that means turning down a cigarette or second helping of dessert.
Too long; didn't read? In theory, the easiest time to ditch an unhealthy habit should be during the middle of the second half of your cycle (or about 21 days after you get your period, if you have a 28-day cycle). However, the best time to change your behavior is any time stress levels are low, no matter what time of month. So don't wait!
This article originally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.