Health effects of snus use : cardiovascular diseases, weight gain and obesity

Sammanfattning: Use of snus is most prevalent in Nordic countries, and especially in Sweden, where 18% of men and 3% of women are daily users. Snus is also used to a minor extent in the United States where an increasing interest is seen for the product. The high levels of nicotine in snus could affect risk of cardiovascular disease (CVD) and may lead to metabolic disturbances, but the extent of these potential effects is not completely understood. The aims of this thesis were to assess the associations between use of snus and CVD and excess body weight. The study-specific aims were to assess the impact of snus use on risk of ischemic heart disease (IHD) and stroke (Study I), acute myocardial infarction (AMI) (Study III), and stroke and its subtypes (Study IV). Further, the specific aim of Study II was to assess the association between snus use and weight gain and obesity. Study I was based on a subset of the Swedish Twin Registry and Study II on the Stockholm Public Health Cohort. In Studies III and IV, data from the Swedish Collaboration on Health Effects of Snus Use were analysed. This collaboration was set up to increase the understanding of health effects of snus use and comprises the study populations from Studies I and II, and six other Swedish cohorts. Current snus use was considered the exposure and never users of tobacco or non-current snus users acted as the reference category. In studies of the risk of CVD, participants were followed in the Inpatient Register and the Cause of Death Register for incident events. In Study II, of the associations between snus use and weight gain and obesity, information on tobacco use as well as height and weight was collected via self-administrated questionnaires on two occasions five years apart. A weight gain of more than 5% during follow-up was considered an event, as was reaching a body mass index (BMI) ≥30. Study-specific and pooled hazard ratios (HR) with 95% confidence intervals (CI) of incident events of CVD and risk of death following a CVD were calculated using Cox proportional hazards regression models with attained age or age at diagnosis as the time scale. Logistic regression was used to estimate odds ratios (OR) and 95% CI of case-fatality (within 28 days) after a CVD, as well as the association between snus use and weight gain and incident obesity. No increased risk of CVD was observed among snus users compared to non-users when followed for the maximum time of follow-up. Case-fatality after an AMI or a stroke, regardless of subtype, was increased among snus users, as was risk of death during total time of follow-up. The adjusted ORs of 28-day case-fatality following an AMI or stroke were 1.28 (95% CI 0.99–1.68) and 1.42 (95% CI 0.99–2.04), respectively. Use of snus was also associated with weight gain (OR 1.31, 95% CI 1.04–1.65) and incident obesity (OR 1.93, 95% CI 1.13–3.30) in adjusted models. In conclusion, snus use appears to be associated with both weight gain and obesity, indicating a possible metabolic effect of nicotine. Although snus use was not associated with incident CVD, use was associated with case-fatality and risk of death among those who suffered an AMI or a stroke. Confounding could not be ruled out as a potential explanation for the relationships between snus use and either weight gain/obesity or CVD prognosis.