New research examines the connection between impulse shopping and menstruation. In a study of 443 women, a pair of British researchers discovered that women were more likely to make impulsive purchases during the weeks between ovulation and menstruation, known as the luteal phase of the menstrual cycle.
The study is part of a growing scientific focus on how the ebb and flow of hormones throughout the menstrual cycle influences how the brain processes rewards. Much of the work so far has focused on drugs, particularly stimulants, whose effects seem to vary along with women’s cycles. I wrote about this research in a recent issue of Scientific American Mind:
Researchers believe that estrogen spurs addiction by stimulating the brain’s reward pathways, enhancing the “high” from drugs. Administering estrogen to rats that have had their ovaries removed boosts levels of dopamine, a neurotransmitter involved in the perception of rewards such as food, sex and drugs.
In female mammals, estrogen does not act alone, however. Its hormonal partner, progesterone, appears to oppose estrogen’s ability to promote addictive tendencies. In 2006 [neuroscientist Jill B. Becker of the University of Michigan] reported that giving both estrogen and progesterone to female rats lacking ovaries does not accelerate obsessive cocaine use in the rodents, suggesting that progesterone may be an antidote to estrogen’s pleasure-seeking influence.
And more recent work confirms that women’s response to drugs varies across the menstrual cycle, as the relative levels of estrogen and progesterone naturally wax and wane. In a 2007 study clinical neurobiologist Suzette M. Evans of Columbia University and the New York State Psychiatric Institute and her colleagues found that stimulants are far more pleasurable to women during the estrogen-dominated follicular phase, which occupies the approximately two weeks from the onset of a woman’s period until she ovulates, than during the luteal phase after ovulation, when both estrogen and progesterone are high.
The drug findings have implications for treatment–studies have suggested that artificially boosting a woman’s progesterone can reduce drug cravings (strangely, the same treatment doesn’t seem to work for men). And one 2008 paper demonstrated that women have an easier time quitting smoking if they attempt to do so during the second half of their cycles–between ovulation and menstruation–when progesterone levels are high.
And the findings are beginning to expand outwards from drugs:
A woman’s perception of other kinds of rewards—such as money, food and sex—may also vary during her menstrual cycle. In a 2007 study researchers at the NIH scanned women’s brains using functional MRI as the women played slot-machine games. They found that women’s reward circuitry was more active when they won jackpots during the estrogen-governed phase of their cycles than during the progesterone-infused phase that follows. The ebb and flow of female hormones could thus have broad effects on the perception of pleasures and incentives, influencing women’s motivation to engage in a wide variety of behaviors.
The new study on shopping doesn’t totally jibe with these findings. Impulse buying, the new data show, is more likely during the progesterone-dominant luteal phase, when pleasurable activities seem less rewarding. If rewards are less potent during this period of the menstrual cycle, one would think that it would be easier to exercise willpower–and thus refrain from shopping.
But the connection between rewards and behavior is not always that straightforward. For instance, perhaps women shopped more during the second halves of their cycles because normally fun activities weren’t giving their brains the same jolt of pleasure. If progesterone is blunting the effects of rewards, it could spur women to engage in more pleasurable activities–such as impulse shopping–just to generate the same “high.”
Reference: Pine, K., & Fletcher, B. (2010). Women’s spending behaviour is menstrual-cycle sensitive Personality and Individual Differences DOI: 10.1016/j.paid.2010.08.026