Who are they?
The AMORIS cohort includes a total of 812,073 subjects (49% men and 51% women) with information from laboratory analyses of blood and/or urine samples obtained between 1985 -1996 on a varying number of biomarkers, in all representing 35,830,287 analyses.
All individuals were either healthy individuals referred for clinical laboratory testing as a routine part of yearly health check-ups through occupational health care or outpatients referred for laboratory testing. These two populations may be distinguished in the database by a specific code of payment. Of the laboratory analyses, 26% represented routine health screenings, 24% health care in the occupational setting and 50% other outpatient care. In addition to the blood samples, there is information on fasting status and for many subjects also information regarding body weight and height from the health examinations
The subjects of the AMORIS cohort coming from occupational routine health screenings represent a large number of companies and a broad range of branches including administrative, industrial, technology, trade, research and other activities in the greater Stockholm area. They were invited by their employer as an optional employment benefit to regular health check-ups according to standardized programs run by physicians at various health centres. More than 50% of the subjects followed a regular and individualized scheme of health check-ups on regular time intervals. No individuals were inpatients at the time their blood or urine samples were taken and none were excluded for disease symptoms or because of treatment.
All subjects of the AMORIS cohort were residents of Sweden and were predominantly living in Stockholm County (67%) at the time of the health examination and inclusion in the cohort. During the inclusion period (1985-1996) the total population of Stockholm County was about 1.6 million inhabitants. Thus, the AMORIS cohort constituted a substantial part (about 35%) of the total population of Stockholm County at that time and with respect to working ages this proportion was even higher.
By linkage of the AMORIS cohort to national Censuses for the period 1970-1990, a detailed characterization of the cohort with regard to socio-demographic factors has been possible. These censuses were mandatory for adult Swedish citizens and with basically no loss to participation. The censuses included questions about housing, marital status, country of birth, occupation and education. Based on this information, an index of socioeconomic status (SEI) was derived distinguishing unskilled and skilled workers from lower intermediate and higher employees.
The sex and age distribution of the AMORIS cohort at the time of inclusion compared to the general population of Stockholm County in 1990 is shown in Table 1. The mean age at the time of first blood sampling was 42.6 years, which was about four years older than the general population of Stockholm County. As can be seen from Table 1 the proportion of subjects born outside of Sweden was similar between the AMORIS cohort and the general population of Stockholm County in 1990. The subjects of the AMORIS cohort had a somewhat higher education and a larger proportion was married. About 90% of subjects between 20 and 64 years old were employed, which was a somewhat higher proportion than the general population of Stockholm County in 1990.
The gainfully employed subjects of the AMORIS cohort represent a wide range of occupations. The specific occupations represented in the AMORIS cohort identified by the three digit Nordic Occupational Classification (NYK) code include several different blue collar as well as white collar occupations predominantly found in a more urban environment. For example, the proportion of farmers was less than 1% of all gainfully employed subjects. Importantly, among those employed, the socioeconomic distribution of the AMORIS cohort was very similar to that of the population of Stockholm County in 1990 according to the national census (Table 1). The proportion of workers or lower employees was 45% in the total employed population of Stockholm County and 43% in the AMORIS cohort. The comparatively high proportion of employed subjects in the AMORIS cohort reflects the recruitment to laboratory testing by occupational health screening and is reflected in a lower all-cause mortality (Standardized Mortality Ratio (SMR): 0.86) in the AMORIS cohort compared to the general population during the period 1985-2012.
Table 1. Sociodemographic characteristics of subjects in the AMORIS cohort at the time of inclusion (1985-1999) compared to the general population of Stockholm County in 1990.