Smoking is an extremely common habit amongst schizophrenics. In the USA, some 90 per cent smoke compared to only 33 per cent of the general public. Masterson and O'Shea compared cigarette smoking prevalence of Dublin's schizophrenic in-patients with that of the general pubic. They concluded that while 92 percent of male and 82 percent of female Irish schizophrenics smoked, prevalence was only 49 percent and 36 percent respectively for the general public. Every available study on the topic of which the authors are aware, therefore, suggests the schizophrenics are much more likely to smoke than are other members of the population. Not only do schizophrenics typically smoke, but they tend to live more frequently in selenium deficient regions. As a consequence, they often lack adequate glutathione peroxidase, the selenoenzyme which forms a key component in the body's defences against smoking-induced free radical damage.