Environmental and Occupational Noise Exposure in Relation to Incidence of Type 2 Diabetes

Study subjects

Nine Scandinavian cohorts constitute the sampling frame for the study. Four cohorts were recruited in Stockholm County: [Stockholm Diabetes Preventive Program (SDPP), 60-year old men and women (Sixty), Twin Registry (SALT) and Swedish National Study of Aging and Care in Kungsholmen (SNAC-K)], with a total of more than 22 500 participants. The Malmö Diet and Cancer (MDC) study recruited 28 098 men and women living in the city of Malmö. The Danish Diet Cancer and Health (DCH) cohort enrolled 57 053 subjects from the greater Copenhagen or Aarhus areas. The Swedish Mammography Cohort (SMC) recruited 13 680 women esiding in the Uppsala area. The Danish Nurse Cohort (DNC) included 28 731 female nurses from the whole of Denmark. The Danish National Health Survey (DNHS) included 177 639 persons randomly selected across Denmark. Overall, enrollment focused on ages 16 to 99 years and occurred 1992-2013. The study subjects answered questionnaires at recruitment on lifestyle factors, health status and socioeconomic characteristics.

Exposure assessment

Traffic noise: Transportation noise exposure is assessed based on well validated models. Road traffic and railway noise are modelled using the Nordic Prediction Method or an update of this method. For road traffic noise the input variables include geocodes, screening by terrain and buildings, and information on annual average daily traffic, distribution of light/heavy traffic, travel speed, and road type for all major road links. Railway noise is calculated for all addresses within a 1000 m buffer around all railway tracks. Input variables include geocodes, screening by terrain and buildings, and average number of trains per period (day/evening/night), train types, and travel speed. In addition, cities with trams and/or metro include these in the calculations. Aircraft noise is estimated using noise maps obtained from local or national authorities.

Detailed noise assessments have been performed every fifth or tenth year and noise levels for the years between those with estimates are calculated based on linear interpolation or other approximation methods. For each participant, the time-weighted average noise exposure from each traffic noise source during follow-up is calculated, taking into account all addresses where the subject has lived, and considering the duration of residence at each address. In addition, combined exposure to multiple traffic noise sources is estimated.