Tobacco Research Explores Why Quitting Can Be So Hard
> 11/9/2007 12:27:38 PM

After a consistent downward trend spanning more than two decades, smoking rates in the United States have leveled off, hovering at approximately 21% for more than 3 years. Unfortunately, nearly 1 in 4 men and 1 in 5 women still smoke, and the stated goals of national tobacco control groups to bring levels down to 12% by 2010 seem unlikely. It's not that more smokers have simply accepted their deadly habit: a large percentage still try to quit at least once every year, with nearly half abstaining for more than one day, and it would seem that the difficulty smokers encounter when trying to quit plays a major role in the leveling of national trends. So why is quitting so hard?  

Two new animal-based studies
further illuminate the chemical relationship between the brain and the powerful effects of nicotine, explaining why some are more susceptible to addiction and why quitting often proves so impossibly difficult. The first study's most interesting revelations concern stress and the literal difference between night and day: melatonin, a hormone produced by the body in response to darkness, dilutes the effects of nicotene, which explains why habitual smokers often speak of the day's first cigarette as a particularly pleasurable experience akin to a morning cup of coffee. Most smokers also report lighting up more often while anxious, and the common perception of tobacco as a stress reliever for addicts appears to be accurate: the effects of nicotene in rats were strongest during periods when the body's production of stress hormone corticosterone was at its high point.

The second study hinted at the early-smoking phenomenon in which patients who started early grow more dependent on nicotine and find it harder to quit: the substance produced depression and anxiety-like symptoms in adolescent rats. When the same rats were deprived of the drug, they became far more sensitive to stressful situations. The rats who'd been receiving nicotine shots, for example, gave up on a swimming test with a liquid sugar reward far sooner than their control group counterparts. In humans, these sensations only reinforce the pre-existing addiction; stressful situations make it harder for smokers to resist, even if they're trying to quit. This finding reinforces the above conclusion regarding stress hormones.

Smoking has been linked to depression and anxiety before, but this study clearly illustrates how early exposure to nicotine leaves the brain predisposed to such conditions. The nicotine-addicted rats showed less interest in earning rewards or exploring new environments, indicating that their sense of pleasure and security had been compromised by the presence of nicotine in their developing brains. More research is required, but the team believes that structural changes in the brain's reward-centered dopamine delivery system are the most likely culprits. They plan, in future studies, to explore whether SSRI antidepressants could help reverse this trend.

We understand better than ever the many pernicious effects tobacco has on the lungs, the the digestive system and, of course, the brain. And we understand why, after the fateful decision to smoke that first cigarette begets a terrible habit, giving it up requires far more than mere desire. But quitting is by no means impossible: half of the 91 million living Americans who have ever smoked somehow managed to do it. But specially designed chemical and hormonal treatments will most likely make the process a lot easier in the near future.

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