It has long been recognized that men and women react to nicotine differently, with women being more resistant to NRT and more likely than men to relapse when trying to give up smoking.

The findings of the study could explain various behavioral variations among women smokers, including why they are more resistant to quitting smoking than men.

A single cigarette’s worth of nicotine inhibits estrogen production in women’s brains.

This could explain various behavioral variations among women smokers, including why they are more resistant to quitting smoking than men.

This paper is presented for the first time at the ECNP Congress in Vienna.

“For the first time,” says lead author Erika Comasco, “we can see that nicotine works to shuts down the estrogen production mechanism in the brain of women. 

The study authors “were surprised to see that this effect could be seen even with a single dose of nicotine, equivalent to just one cigarette, showing how powerful the effects of smoking are on a woman’s brain.”

“This is a newly-discovered effect, and it’s still preliminary work,” adds the lead author. 

“We’re still not sure what the behavioural or cognitive outcomes are; only that nicotine acts on this area of the brain, however we note that the affected brain system is a target for addictive drugs, such as nicotine”.

The effect has been observed in the thalamus, which is part of the brain’s limbic system. This system is involved in regulating behavior and emotions.

Researchers from Sweden’s Uppsala University worked with ten healthy women who volunteered. In addition to receiving an intranasal dose of nicotine from a commercial source, the women received an injection of a radioactive tracer bound to an enzyme called aromatase, also known as estrogen synthase, which binds to estrogen. Aromatase is the enzyme that produces estrogen.

Researchers were able to see both how much aromatase was in the brain and where it was by using MRI and PET scans. Researchers found that a single dose cut the amount of aromatase in the brain by a small amount.

It has long been recognized that men and women react to nicotine differently, with women being more resistant to NRT and more likely than men to relapse when trying to give up smoking.

However, it is unclear what biological factors led to these variations. This inhibiting effect on aromatase synthesis has never before been shown in people. The impact on men was not investigated.

“This discovery leads us to believe,” adds professor Comasco, “that nicotine’s effect on estrogen production has a significant impact on the brain, but perhaps also on other functions, such as the reproductive system – we don’t know that yet.”

When it comes to smoking, men and women react in very different ways. Women appear to be more resistant to nicotine replacement therapy, they experience more relapses, they are more susceptible to the heritability of smoking, and they are at a higher risk for acquiring smoking-related main illnesses, such as lung cancer and heart attacks.

“We need now to understand if this action of nicotine on the hormonal system is involved in any of these reactions,” adds the author.

“Of course this is a comparatively small group of women, we need a larger sample to confirm these findings. Nevertheless, the message is that nicotine has various effects on the brain, including on the production of sex hormones such as estrogen”.

Professor Wim van den Brink of the Academic Medical Center, University of Amsterdam, who is emeritus professor of psychiatry and addiction, commented:

“This is indeed an important first finding,” comments professor Wim van den Brink of the Academic Medical Center, University of Amsterdam, who was not involved in the study. 

“Smoking has many adverse effects in men and in women,” according to the professor, “but this particular effect of nicotine on the reduction of estrogen production in woman was not known before. It should be noted, however, that tobacco addiction is a complex disorder with many contributing factors. 

“It’s unlikely that this specific effect of nicotine on the thalamus (and the production of estrogen) explains all the observed differences in the development, treatment and outcomes between male and female smokers. 

“It is still a long way from a nicotine induced reduction in estrogen production to a reduced risk of nicotine addiction and negative effects of treatment and relapse in female cigarette smokers, but this work merits further investigation”.

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