UNDER THE MICROSCOPE:Everybody knows that smoking kills, that it causes cancer, that it lays waste to our lungs, but so many still do it, writes DR WILLIAM REVILLE.
WE HAVE A little dog called Milo. I don't think he is exceptionally bright. He is probably of average dog intelligence. Nevertheless, I would be disappointed if he didn't know that smoking cigarettes is very bad for your health, given the massive public education on the dangers of tobacco and the anti-smoking campaigns we have had in Ireland over the last 10 years. Even the pack of cigarettes you buy bears the legend "Smoking Kills". Everybody knows the dangers, and yet the latest survey shows that there has been no significant decrease in rates of smoking in Ireland over the last 10 years. Why is smoking such a hard nut to crack?
The latest research in America claims that smoking becomes an addictive habit amazingly quickly. This work is described by Joseph DiFranza in this month's Scientific American. DiFranza developed a question checklist called the Hooked on Nicotine Checklist (Honc), where a "yes" answer to any question is taken to indicate that addiction has begun. Honc was administered to hundreds of adolescents and, surprisingly, symptoms of addiction appeared within the first weeks of smoking even though the average adolescent in the survey was only smoking two cigarettes a week. Symptoms of addiction in Honc include cravings for cigarettes and failed attempts to quit.
It is known that chronic exposure to high doses of nicotine stimulates an increase in neuron receptors for nicotine in the brain. Research on rats, stimulated by DiFranza, has found that the nicotine equivalent of even half a cigarette is sufficient to cause a significant increase in brain neuron receptors.
The difficulty in giving up addictive drugs is overcoming the difficult withdrawal symptoms. Addictive substances increase the production of certain chemicals in the brain. The body responds by inhibiting these chemicals, but, when the user stops taking the drug, the inhibition is now excessive and causes withdrawal symptoms to appear. In the early stages of smoking addiction, DiFranza describes how smoking a single cigarette can suppress withdrawal symptoms for weeks, but, after long-term smoking, cravings to smoke another cigarette set in within an hour or two of smoking the previous one. Smoking the next cigarette removes the withdrawal symptoms and, in fact, withdrawal symptoms are the cause of long-term heavy smoking.
So the picture is, if you start off smoking only one or two cigarettes a day and then quit, you may not experience withdrawal symptoms for a couple of weeks and you can quieten these withdrawal symptoms by smoking another cigarette. The symptom-free interval between the last cigarette and the onset of withdrawal symptoms is called latency to withdrawal. This can shrink from weeks to minutes over many years of smoking. DiFranza noted that adolescents smoking two cigarettes a day took, on average, two years before they built up to five cigarettes a day.
DiFranza also describes other research involving neuro-imaging that purports to show that the brain quickly becomes sensitised to nicotine so that addiction can appear after just a few doses.
DiFranza's model is built entirely on physiology whereas the mainline assumption among researchers who study smoking has long been that the roots of addiction lie in psychology. The long-term goal of DiFranza's studies is to identify drugs that can treat or cure this physiological smoking addiction.
Perhaps DiFranza is right but I find it hard to believe that physiology is the entire answer to the smoking addiction. There is so much evidence in other addictions that psychology is important - placebos have been shown to ease heroin withdrawal symptoms.
An unfortunate side-effect of the physiological model is that people who have taken up smoking, but who are not far advanced into the habit, can become demotivated in their efforts to quit by believing they are suffering from a purely physical disorder. Even if DiFranza is right, there is no drug available now to treat the smoking addiction, other than nicotine-replacement therapy, which fails in the majority of cases. And yet it is common experience that people quit smoking every day, even heavy smokers, and mostly without suffering more than mild discomfort.
There are many dimensions to the smoking phenomenon other than the purely physiological, eg poorer socioeconomic groups smoke much more than better off people. Smoking is indeed a scourge in our society but despite universal knowledge of the dangers of smoking, smoking rates remain high. Clearly changing the level of risk awareness of the population is a different matter to changing behaviour.
Appeals to rationality and self-interest have failed to have an overall impact. I don't know what will work. Perhaps we should start appealing to peoples' higher nature.
I have just read this article to Milo and he is vigorously wagging his tail.
William Reville is associate professor of biochemistry and public awareness of science officer at UCC - understandingscience@ucc.ie