Smokeless tobacco (snus) is associated with an increased risk of type 2 diabetes: results from five pooled cohorts

In order to investigate potential selection bias in population-based cohort studies, participants (n = 28098) and non-participants (n = 40807) in the Malmö Diet and Cancer Study (MDCS) were compared with regard to cancer incidence and mortality. MDCS participants were also compared with participants in a mailed health survey with regard to subjective health, socio-demographic characteristics and lifestyle. Cancer incidence prior to recruitment was lower in non-participants, Cox proportional hazards analysis yielded a relative risk (RR) with a 95% confidence interval of 0.95 (0.90-1.00), compared with participants. During recruitment, cancer incidence was higher in non-participants, RR: 1.08 (1.01-1.17). Mortality was higher in non-participants both during, 3.55 (3.13-4.03), and following the recruitment period, 2.21 (2.03-2.41). The proportion reporting good health was higher in the MDCS than in the mailed health survey (where 74.6% participated), but the socio-demographic structure was similar. We conclude that mortality is higher in non-participants than in participants during recruitment and follow-up. It is also suggested that non-participants may have a lower cancer incidence prior to recruitment but a higher incidence during the recruitment period.

The Stockholm Public Health Cohort was set up within the Stockholm County Council public health surveys to inform on determinants and consequences of significant contributors to the current burden of disease. Participants are 89 268 randomly selected individuals from the adult population of Stockholm County. Baseline surveys took place in 2002, 2006 and 2010 via self-administered questionnaires. So far, participants recruited in 2002 were re-surveyed twice, in 2007 and 2010, and those enrolled in 2006 were re-surveyed once, in 2010. Self-reported data are regularly supplemented by information from national and regional health data and administrative registers, for study participants and their relatives (including their offspring). Available data are extensive and include a wide array of health, lifestyle, perinatal, demographic, socio-economic and familial factors. The cohort is an international resource for epidemiological research, and the data available to the research community for specific studies obtained approval from the Stockholm Public Health Cohort Steering Committee and the Stockholm Regional Ethical Review Board.