According to a new study by scientists at the University of Minnesota, differing levels of female sex hormones during the menstrual cycle are the reason for some women's inability to quit smoking.
The researchers studied a total of 200 women who wanted to quit smoking. One group of women tried to give up smoking in the "follicular" stage of their menstrual cycle - the period leading up to ovulation, when an egg is produced by the ovary. Another set of women tried to quit smoking in the "luteal" stage, the approximate two-week stage that completes the cycle.
After 30 days, 86% of the women who were trying to give up smoking during their follicular phase had succumbed to the need and smoked at least one cigarette.
Compared to this, the success rate was better for those women in the luteal phase. Only 66% of the group who had started in their luteal phase felt the need and smoked at least one cigarette.
The researchers suggest that sex hormones - the main ones being estrogen and progesterone - impact a woman's quitting resolve. They also believe the hormones could influence the speed at which nicotine is removed from the blood.
There is already evidence of the link between menstrual periods and mood swings in women, but this latest research could help explain why women smokers tend to smoke more at some points of the cycle.
Writing in the journal Addiction, the researchers wrote: "Our findings support an important role for ovarian hormones in smoking cessation."
"More research is needed to understand these biological mechanisms," they added.
A spokesman for the charity smoking Quit said: "Women reading this report shouldn't panic about the findings, as there's lots of help available regardless of the time of the month."
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