Smoking and mental health - NCSCT

Epidemiology of the association between smoking and mental disorders 4
significant association between smoking and the incidence of bipolar disorder in
adults (IRR = 6.45, 95% CI 0.55–75.65), 3 but numbers were small with only nine
incident cases in the cohort. Conflicting results were seen for the impact of
bipolar disorder on onset of smoking in adolescence, where one study showed a
significant sevenfold increase in the onset of heavy smoking in adolescents (OR =
7.1, 95% CI 1.9–25.9), 27 but no significant association with onset of
light/moderate smoking in adolescents (OR = 0.9, 95% CI 0.3–2.7).
Furthermore, no significant association was seen between the impact of bipolar
disorder on the onset of smoking in adults in two studies (OR = 0.3, 95% CI
0–3.3; 27 magnitude of effect was not reported, 3 except p >0.05).
4.6 Smoking and schizophrenia
Five cohort or longitudinal studies of the association between smoking and
schizophrenia were identified in our literature search, and these are summarised
in Table A3. Two of these are large cohort studies of young male army recruits,
from Israel and Sweden, and report conflicting results. 28,29 The study from Israel
reported an almost twofold increase in the risk of incidence schizophrenia among
smokers (OR = 1.94), 29 but the Swedish study, which involved a much larger
sample (48,772 vs 14,248) and number of incident cases of schizophrenia (350 vs
44), found no excess risk (OR = 0.80). 28 Another study demonstrated that the
time between initiation of smoking and the onset of the mental health illness was
much shorter for schizophrenia than for other psychoses. 30 A more recent
prospective study 31 in Danish women found that being a smoker increased the
risk of developing schizophrenia spectrum disorder by about 40% (OR = 1.42,
95% CI 1.12–1.80), with some evidence that risk increased with the number of
cigarettes smoked per day. The study also reported an increased risk of affective
spectrum disorder in those who smoked (OR = 1.40, 95% CI 1.05–1.86). One
further study recruited 48 participants aged 12–30 years with prodromal
symptoms (and thus at risk of developing schizophrenia) who participated in the
Cognitive Assessment and Risk Evaluation (CARE) programme. 32 The study
demonstrated that nicotine use was significantly associated with the development
of schizophrenia (p = 0.005, Fisher’s exact test). 32
Due of the lack of prospective studies, we examined an existing systematic
review of schizophrenia and smoking, based on 42 cross-sectional studies from 20
countries, by de Leon and Diaz. 33 The combined OR for current smoking among
those with schizophrenia, compared with the general population, was 7.2 (95% CI
6.1–8.3) and 3.3 (95% CI 3.0–3.6) among males and females, respectively, but few
studies had adjusted for confounding. Combining these pooled estimates with
three results reported subsequently in four published studies 34–37 produces an OR
of 4.62 (95% CI 2.15–9.92, p