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Bjorngaard, J. H., Gunnell, D., Elvestad, M. B., Davey Smith, G., Skorpen, F., Krokan, H., et al. (2013). The causal role of smoking in anxiety and depression: a Mendelian randomization analysis of the HUNT study. Psychol Med, 43(4), 711–719.
Abstract: BACKGROUND: Cigarette smoking is strongly associated with mental illness but the causal direction of the association is uncertain. We investigated the causal relationship between smoking and symptoms of anxiety and depression in the Norwegian HUNT study using the rs1051730 single nucleotide polymorphism (SNP) variant located in the nicotine acetylcholine receptor gene cluster on chromosome 15 as an instrumental variable for smoking phenotypes. Among smokers, this SNP is robustly associated with smoking quantity and nicotine dependence. Method In total, 53 601 participants were genotyped for the rs1051730 SNP and provided information on smoking habits and symptoms of anxiety and depression using the Hospital Anxiety and Depression Scale (HADS). RESULTS: Self-reported smoking was positively associated with the prevalence of both anxiety and depression, and the measured polymorphism was positively associated with being a current smoker and the number of cigarettes smoked in current smokers. In the sample as a whole, risk of anxiety increased with each affected T allele [odds ratio (OR) 1.06, 95% confidence interval (CI) 1.02-1.09, p = 0.002] but there was no association with depression (p = 0.31). However, we found no clear association of the polymorphism with either anxiety (OR 1.03, 95% CI 0.97-1.09, p = 0.34) or depression (OR 1.02, 95% CI 0.95-1.09, p = 0.62) among smokers. CONCLUSIONS: As there was no association of the smoking-related rs1051730 SNP with anxiety and depression among smokers, the results suggest that smoking is not a cause of anxiety and depression.
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Ness-Jensen, E., & Lagergren, J. (2017). Tobacco smoking, alcohol consumption and gastro-oesophageal reflux disease. Best Pract Res Clin Gastroenterol, 31(5), 501–508.
Abstract: Gastro-oesophageal reflux disease (GORD) develops when reflux of gastric content causes troublesome symptoms or complications. The main symptoms are heartburn and acid regurgitation and complications include oesophagitis, strictures, Barrett's oesophagus and oesophageal adenocarcinoma. In addition to hereditary influence, GORD is associated with lifestyle factors, mainly obesity. Tobacco smoking is regarded as an aetiological factor of GORD, while alcohol consumption is considered a triggering factor of reflux episodes and not a causal factor. Yet, both tobacco smoking and alcohol consumption can reduce the lower oesophageal sphincter pressure, facilitating reflux. In addition, tobacco smoking reduces the production of saliva rich in bicarbonate, which is important for buffering and clearance of acid in the oesophagus. Alcohol also has a direct noxious effect on the oesophageal mucosa, which predisposes to acidic injury. Tobacco smoking cessation reduces the risk of GORD symptoms and avoidance of alcohol is encouraged in individuals where alcohol consumption triggers reflux.
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