Current research program and linkages

A current research program is focused on investigation of metabolic abnormalities and inflammation in relation to chronic disease, primarily cardiovascular diseases, kidney disease, cancer, dementia, rheumatoid arthritis and psychiatric illness.

Several projects have been performed and are ongoing or planned within this research program. This includes research on cardiovascular diseases, cancer, dementia, renal disease, and neurological disorders. For the purposes of this research program the AMORIS cohort has been linked to a number of registers and data bases using the Swedish unique personal identification number.

For data integrity purposes the information depicted in Figure 1 is divided into three major parts that have separate identity codes for each subject: 1) cardiovascular diseases 2) cancer and 3) rheumatoid arthritis. These three different parts of the database contain all information from all sources described in the Figure except the quality registers for each disease area that are only included in the respective disease area part. The respective registers and databases are briefly presented below.

Details of our paper on the AMORIS cohort are given below in our publication in IJE [1]. Some parts of the paper can be found in the forthcoming text below regarding methods, linkages, procedures and some publications.

[1] Walldius G, Malmstrom H, Jungner I, de Faire U, Lambe M, Van Hemelrijck M, Hammar N. Cohort Profile: The AMORIS cohort. International Journal of Epidemiology, 2017, 1103–1103i. doi: 10.1093/ije/dyw333

National Health registers, migration, social and family registers

The major National Health registers of Sweden include the National Cause of Death Register (1985-2011), the National Cancer Register (1958-2011), the National Patient Register (regional information 1964-1986; national information 1987-2011, including specialized outpatient care from 2001), the National Medical Birth Register (1973-2011) including the National Register of Congenital Malformations (from 1964) and the National Prescribed Drug Register (2005-2011). By means of record linkage to these registers it has been possible to identify all deaths after the first blood sampling, all diagnosed cancers prior to and following blood sampling going back to 1958 and all hospitalizations from 1964 regionally, from 1970 for Stockholm County and from 1987 nationally.

Information from the Medical Birth Register provides information on pregnancies and deliveries for women in the AMORIS cohort. This includes information on tobacco smoking before and during pregnancy. In addition, for all members of the cohort born 1973 or later (n=64,619) there is information on birth weight and height as well as complications at delivery, including congenital malformations and other birth related factors. Together with information from the Multi Generation Register, it is possible to retrieve information on parity and age at first child birth.

To characterize the AMORIS cohort with regard to socio-demographic factors, the cohort has been linked to National Censuses 1970, 1980, 1985 and 1990. National Censuses were mandatory by law and performed in Sweden every five or ten years during the period 1960-1990. They covered information about country of birth, marital status, employment status, education, occupation and socioeconomic group. For information post 1990, the database was linked to the Longitudinal integration data base for health insurance and labour market studies (LISA register by its Swedish acronym) [1] thereby covering essentially corresponding information for the period 1990-2010. Furthermore, information on all emigration out of Sweden and immigration into the country was captured from 1968 and vital status onwards through linkages with the National Register of the Total Population.

Lifestyle, twins, comorbidity and quality of care registers

To obtain information on lifestyle factors, the AMORIS cohort was linked to a number of research cohorts from Karolinska Institutet: the WOLF study [2], the study of 60-year old men and women in Stockholm [3], a primary prevention program in Sollentuna municipality of Stockholm county [4], the Swedish mammography cohort [5], the EIRA cohort [6], and a cohort for studies of nutritional factors [7]. As a result, information on key risk factors for chronic diseases including tobacco smoking, low physical activity, poor diet, alcohol intake, obesity and hypertension could be obtained for many, but not all of subjects in the AMORIS cohort. Information on tobacco smoking is available for more than 270,000 subjects. Since much of the smoking data stems from the Medical Birth Register, smoking status is known for 35% of women but only for 5% of men. Information on body mass index (BMI) is available for almost 300,000 subjects (37%). Physical activity and blood pressure/hypertension is known for about 10% of the cohort, with slightly higher proportions for men as compared to women.

The AMORIS cohort also includes information from the Swedish twin registry: 9,729 twins were identified in the cohort of whom 4,689 were men and 5,040 were women. There were 1,624 complete twin pairs, of which 536 were monozygotic, 1,043 dizygotic and 45 had unknown zygosity. The Swedish twin registry [8] contains information on health and life style factors and was collected from a number of questionnaires during 1961-1996.

To obtain more detailed clinical information for major diseases, the AMORIS cohort was linked to various “quality of care registers” containing more complete information on diagnosis, treatment and disease characteristics. For cardiovascular (CV) diseases, the AMORIS cohort was linked to SWEDEHEART [9], which during the latter part of the observation period had a nationally more or less complete coverage of all patients treated at a Coronary Care Unit, undergoing Coronary Artery Bypass Surgery angiography or PCI. For patients with stroke, data from RIKSSTROKE was added [10]. For patients with diabetes, information was obtained from the National Diabetes Register (NDR) [11]. Additional clinical information has been retrieved from clinical quality registers for prostate-, breast- and colorectal cancer as well as for patients with rheumatoid arthritis (Swedish RA register) [12] and end stage renal diseases (Swedish kidney register) [13].

References in the AMORIS cohort paper

1. LISA.…

2. Alfredsson L, Hammar N, Fransson E et al. Job strain and major risk factors for coronary heart disease among employed males and females in a Swedish study on work, lipids and fibrinogen, Scandinavian Journal of Work, Environment and Health, 2002;28(4):238-48.

3. Gigante B, Leander K, Vikstrom M et al. Elevated ApoB serum levels strongly predict early cardiovascular events. Heart. 2012;98:1242-45. doi: 10.1136/heartjnl-2012-301852 PMID: 22760866

4. Hellénius ML, de Faire U, Krakau I, Berglund B. Prevention of cardiovascular disease within the primary health care system. Scand J Prim Health Care. 1993;11:68-73

5. Swedish Mammography Cohort (SMC).

6. EIRA.

7. COSM - a cohort of 50,000 Swedish men.…

8. Lichtenstein P, De Faire U, Floderus B, Svartengren M, Svedberg P, Pedersen NL. The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies. J Intern Med. 2002;252:184-205.

9. Swedeheart.

10. Riksstroke, The Swedish Stroke Regsiter.

11. The Swedish National Diabetes Register (NDR).

12. The Swedish Rheumatology Quality Register (SRQ).

13. Svenskt njurregister.

Miranda Beck