BackgroundSelection bias and declining participation rates are of concern in many long-term epidemiological studies. The Västerbotten Intervention Programme (VIP) was launched in 1985 as a response to alarming reports on elevated cardiovascular disease (CVD) mortality in Västerbotten County in Northern Sweden. The VIP invites women and men to a health examination and health counselling during the year of their 40th, 50th, and 60th birthdays.ObjectiveTo evaluate trends in participation rates and determinants of participation in the VIP from 1990 to 2006.DesignRegistry data on socio-economic status from Statistics Sweden, and mortality and hospitalisation data from the National Board of Health and Welfare, both covering the whole Swedish population, were linked to the VIP and analysed for participants and non-participants.ResultsDuring 1990–2006, 117,710 individuals were eligible to participate in the VIP, and 40,472 of them were eligible to participate twice. There were 96,560 observations for participants and 61,622 for non-participants. The overall participation rate increased from 56 to 65%. Participants and non-participants had minimal differences in education and age. Initial small differences by sex and degree of urban residence decreased over time. Despite an increasing participation rate in all groups, those with low income or who were single had an approximately 10% lower participation rate than those with high or medium-income or who were married or cohabitating.ConclusionSustainability of the VIP is based on organisational integration into primary health care services and targeting of the entire middle-aged population. This enables the programme to meet population expectations of health promotion and to identify high-risk individuals who are then entered into routine preventive health care services. This has the potential to increase participation rates, to minimise social selection bias, and to reinforce other community-based interventions.

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Summary.In a nationwide incident case-referent study stepwise univariate analysis has revealed several risk determinants for childhood diabetes mellitus. In a multivariate analysis we have determined the set of risk determinants that would independently predict childhood Type i (insulindependent) diabetes. Possible interactions between the risk determinants and differences in risk profiles with different ages at onset were also examined. Reported familial insulintreated and non-insulin-treated diabetes were significant risk factors in all age groups, as was also a low frequency of milk intake. The frequency of infections and a high intake of foods rich in nitrosamine tended to interact (OR 11.8,p = 0.053) indicating a synergistic effect. A Cox regression analysis revealed that stressful life events during the last year was the only variable that tended to affect the age at onset (p = 0.055). This indicated that psychological stress may rather precipitate than induce Type i diabetes. A short breast-feeding duration (OR = 3.81), and an increased body height (OR = 3.82) contributed significantly to the predictive model in only the youngest age group (0-4 years). An increased frequency of infections in the year preceding onset (OR = 2.15) and no vaccination against measles (OR = 3.33) contributed significantly to the model only in the age group 5-9 years. Various nutrients had different impacts on the risk of developing Type 1 diabetes in different age groups. It is concluded that in the genetically susceptible child, risk factors which are associated with eating habits, frequency of infections, vaccination status, growth pattern and severe psychological stress affect the risk of developing diabetes independently of each other. The set of risk determinants varies with the age at onset. A high frequency of infections and a high frequency of nitrosamine-rich food intake seem to have a synergistic effect on the risk of developing diabetes in childhood.

The difference in celiac disease risk between birth cohorts at comparable ages suggests an opportunity for primary prevention. This highlights the importance of further exploring the role of infant feeding and exogenous factors besides dietary gluten that might initiate or prevent disease development. Moreover, on the basis of postepidemic incidence trends, we speculate that the Swedish epidemic might not have been as unique as thought previously, although its magnitude was striking.

Summary. This study is part of a nationwide case-referent study. All recent-onset Type 1 (insulin-dependent) diabetic children aged 0-14 years in Sweden were invited to participate. Referent subjects matched for age-, sex-and geographical distribution were selected. In all, 338 patients and 528 referent subjects took part. Life events during the last year prior to clinical onset of Type 1 diabetes were recorded on a questionnaire. The total frequency of life events did not differ between diabetic and referent children. However, qualitatively the life events reported by diabetic children revealed a tendency to increased severity. Events related specifically to actual or threatened losses within the family -events that may affect children differently in different age groups -were reported with a significantly higher frequency by diabetic patients than by referent subjects, aged 5-9 years. The relative risk that such events in fact comprise a risk factor for Type 1 diabetes was 1.82 (95% confidence limits 1.09, 3.03). The relative risk was significantly increased even when standardized for possible confounding factors such as age, sex and indices of social status of the family. We conclude that stressful life events, related to actual or threatened losses within the family, occurring in the vulnerable age group of 5-9 years, are associated with the onset of childhood Type 1 diabetes. Such stressful events may in fact be a risk factor for the disease.