Tobacco smoking is by far the most deadly and preventable lifestyle factor for public health, both globally and nationally. Nevertheless, it is estimated that worldwide, more than 1.1 billion adults are smokers. Today, 16% (0.8 million) of the adult population in Denmark are daily smokers, while 23% (1.1 million) consider themselves smokers, and one in four deaths are smoking related. The most effective method of reducing smoking prevalence is by employing a two-tier strategy to 1) prevent adolescents from initiating smoking and 2) offer effective help to smokers to quit.
The aim of this thesis was to evaluate the effect of intensive smoking cessation interventions (ISCI) on successful quitting through different study designs, synthesised from cohort studies and a review of randomised controlled trials. The aim was fulfilled through 4 scientific studies, each with their own objective.
A systematic review with meta-analysis (I) was set up to compare ISCI and shorter interventions in randomised controlled trials (RCT). Initially, 9,569 unique papers were identified, and, after screening for relevant studies, 18 RCTs were included, investigating a total of 10,131 smokers. The studies were primarily conducted in Western Europa and the USA. The body of evidence for three of four outcomes were graded moderate, and the last outcome was graded low. A random effect meta-analysis revealed that smokers randomised to ISCI were significantly more likely to be successful quitters compared to shorter interventions for all four outcomes. The primary outcome (continuous abstinence in the short and long term) increased the chance of success 3-fold.
A methodological study (II) of the Danish National Smoking Cessation Database (SCDB) was undertaken. The development of the SCDB and the most commonly registered smoking cessation interventions (SCI) were described, as were the data collection and validity.
Two cohort studies based on the data from the SCDB were conducted to evaluate the effectiveness of SCI in real life. One study investigated the effectiveness of five different SCIs (III) and found that the intensive Gold Standard Programme’ (GSP - Standard SCI in Denmark) was the only intervention that was effective for both men and women. The other cohort study was set up to investigate the effectiveness of the GSP in a vulnerable subgroup of smokers diagnosed with severe mental disorder (SMD) (IV). The study showed that smokers with SMD were significantly less likely to become successful quitters compared to smokers without mental disorders. However, one in every four smokers with SMD managed to stay continuously smoke-free for at least 6 months compared to one in three in the comparison group. The data were analysed using a mixed-effect logistic regression model. In both cohort studies, compliance was identified as the strongest predictor of a successful outcome.
This thesis adds to the evidence on intensive smoking cessation interventions (ISCI) through different study designs. The results from both study designs favoured ISCI, although the GSP was significantly less effective in smokers with SMD compared to smokers without mental illness. To develop effective SCI in the future, it is important to evaluate the effects in an RCT and to follow-up the post-implementation effects in real life (e.g., through a national SCDB).