Smoking should be considered an "important" risk factor for schizophrenia, a scientist has claimed.
Professor Boris Quednow, from the University Hospital of Psychiatry in Switzerland, led new research suggesting smoking increases the impact of schizophrenia genes.
Healthy smokers carrying the gene variants responded to an "acoustic stimuli" test in the same way as individuals suffering from the serious mental disorder.
The effect also appeared to be stronger the more a person smoked.
The study involved more than 1,800 participants who underwent a simple test which involves listening to a sequence of similar clicks.
Brainwave measurements show that most people suppress other, irrelevant, stimuli while processing the sounds.
However patients with schizophrenia appear to lack this filtering mechanism. As a result their brains are thought to be inundated with too much information.
Psychiatrically healthy people carrying variants of the gene TCF4 that increased the risk of schizophrenia also displayed poorer acoustic filtering, the study found. However, smoking appeared to amplify the effect, resulting in greater deficits.
The findings are published today in the journal Proceedings of the National Academy of Sciences.
Prof Quednow said: "Smoking alters the impact of the TCF4 gene on acoustic stimulus filtering. Therefore, smoking might also increase the impact of particular genes on the risk of schizophrenia.
"Smoking should... be considered as an important cofactor for the risk of schizophrenia in future studies."
People with schizophrenia frequently smoke, the researchers pointed out.
A combination of the click test and genetic and smoking data could be used to diagnose schizophrenia more rapidly and define new patient sub-groups, said Dr Quednow.
Battle the addiction with these top tips by hypnotherapist, Elle Dormer.
"Close your eyes and take 3 deep breaths in and out. Now build a mental picture of yourself in the future as a non smoker. "Make it real by filling in the detail - where you are, what you're doing, who you're with and how much better you look and feel. This is known as future pacing. If you can imagine yourself having achieved your goal you a mentally a step closer to it."
"Smokers often use cigarettes as a form of escapism. To have a break away from their desk after a stressful call. Or to provide thinking time when they are procrastinating. "Go for a brisk walk instead. Or to the kitchen to make a cup of tea. Any simple, familiar task that we can do without much thought allows us to simultaneously access our unconscious or 'zone out' which can be both relaxing and enable greater creative thought."
"Make a list of all the people (alive or dead) in your life who care for you - or have cared for you, like your friends, partner, parents or children. Then close your eyes and imagine them all together gathered in a room. "You are standing before them with a large beautifully gift wrapped box. This present represents you quitting smoking. Explain this to them in your mind. See or imagine their reactions. "Make them real. The relief, love, pride, appreciation. Then imagine asking for the gift back and how sad and disappointed they would be. And resolve that you cannot do this to the people you love."
"Cigarettes do not relax you. Nicotine is a stimulant so it is actually making you edgier and more stressed by elevating your heart rate and releasing stress hormones like adrenalin and cortisol into your blood stream. "Try an experiment: replace one of your regular cigarettes of the day with the following pattern of breathing. Breathe in for a count of 4 and out for a count of 8. Do this 10 x, consciously relaxing your body on every out breath. "This will physiologically de-stress you by slowing your heart rate and releasing endorphins. And prove to you you can truly relax yourself without a cigarette.
"Take a moment somewhere quiet and close your eyes. Remember a time when you felt really confident, relaxed and in control. Take yourself back to that time, fill in the details and make it real. When you're feeling those emotions at their strongest, squeeze our thumb and forefinger together. "Clear your mind and repeat. Then practice recalling those helpful, positive emotions at points during the day by squeezing your thumb and forefinger together. The physical trigger should help to access those beneficial feelings that will help at moments of weakness."