Smoking and mental health - NCSCT

Epidemiology of the association between smoking and mental disorders 4
between per unit increase in depression score at baseline and the transition to
daily smoking 1 year later (OR = 1.01, 95% CI 0.99–1.02). 93
4.10 Smoking and dementia
In 2007, Anstey et al reported a review and meta-analysis of 19 studies published
before June 2005 with at least 12 months of follow-up, including data from over
26,000 participants followed from 2 years to 30 years with respect to incident
dementia and/or cognitive decline. 95 The pooled relative risk for developing
dementia was estimated as 1.27 (95% CI 1.02–1.60, two studies) in current
smokers compared with never smokers, and corresponding relative risks of
incident Alzheimer’s disease and vascular dementia were 1.79 (95% CI 1.43–2.23,
four studies) and 1.78 (95% CI 1.28–2.47, two studies), respectively. A second
systematic review and meta-analysis published in 2008 was conducted in parallel
with the first review, but included more contemporary studies written in English
language and published up to November 2007. 96 The second review reported
essentially similar findings, with a pooled ratio for current smoking and incident
Alzheimer’s disease of 1.59 (95% CI 1.15–2.20, eight studies). The four larger
studies found positive associations between current smoking and incident
dementia (or subtypes), and include a 4-year follow-up of 1,064 participants
aged 65 years and over, 97 a 2-year follow-up of 2,820 participants aged 60 years
and over, 98 a follow-up of 6,870 people aged at least 55 years over an average
period of 2.1 years, 99 and an association between mid-life smoking and late-life
Alzheimer’s disease in 3,734 men with a mean age of around 77 years. 100 Of
these, two reported exposure-related effects, where the risk of dementia increased
with increasing cigarette consumption. 98,100
However, the large studies that found no association between smoking and an
increased risk of dementia include the Canadian Study of Health and Aging (RR
= 0.82, 95% CI 0.57–1.17) 101 and the MRC Cognitive Function and Ageing Study
(RR = 0.90, 95% CI 0.50–1.50). 102 The reason for this heterogeneity is unclear,
although both studies involved relatively long follow-up periods and findings
from the Rotterdam cohort study have suggested a diminution of risk ratio for all
dementia from 2.2 at approximately 2 years 99 to 1.5 at approximately 7 years; 103
it is therefore possible that longer follow-up periods in panel survey designs
obscure the effect because of selective attrition. Relevant studies published since
the systematic reviews mentioned above include two that report positive
associations between smoking and dementia hospitalisation or healthcare
contacts, 104,105 and one reporting a strong association between mid-life smoking
status and late-life dementia risk in 1449 people aged 65–79 years. 106 A recent
review also concluded that studies with tobacco industry affiliation were more
likely to report a protective effect and less likely to report a risk effect than
studies without such affiliation. 107
© Royal College of Physicians 2013 75