The association between high nicotine dependence and severe mental illness may be consistent across countries

Studies all over the world suggest that severe mental illness, including schizophrenia and mood disorders, is associated with tobacco smoking. This study, combining samples from the United States and Spain, had 3 objectives: (1) to test the hypothesis that severely mentally ill patients who smoke are more likely to have a high nicotine dependence when compared with control smokers, (2) to compare frequencies of high nicotine dependence in controls in both countries, and (3) to compare frequencies of high nicotine dependence in severely mentally ill patients in both countries.

Scores on the Fagerström Test for Nicotine Dependence (FTND) for 4 samples of current daily smokers were analyzed. The sample sizes of the U.S. and Spanish control groups were 129 and 646 subjects, respectively. The diagnoses for the U.S. patients were DSM-IV schizophrenia, 74% (89/120), and DSM-IV mood disorders, 26% (31/120). The diagnoses for the Spanish patients were DSM-IV schizophrenia, 87% (173/199), and DSM-III-R mood disorders, 13% (26/199). High nicotine dependence (FTND score > or = 6) was the dependent variable in 5 logistic regression analyses.

The main findings were that (1) severely mentally ill patients had significantly higher frequencies of high nicotine dependence than controls (odds ratio [OR] = 10.59, 95% CI = 7.31 to 15.34) even after controlling for gender, country, interaction between country and mental illness, and age; (2) U.S. controls had significantly higher frequencies of high nicotine dependence than Spanish controls (OR = 3.18, 95% CI = 2.02 to 5.00); and (3) U.S. and Spanish patients did not have significantly different frequencies of high nicotine dependence.

New studies, specially designed to test for transcultural differences in nicotine dependence, are needed to verify that nicotine dependence in severely mentally ill patients is consistently high and similar in different countries.