The Swedish Mammography Cohort
The general aim of the Swedish Mammography Cohort (SMC) - a large population-based cohort of over 60,000 women - is to assess relationships between a number of modifiable factors (diet, vitamin supplement use, physical activity, smoking, alcohol, body weight, other anthropometric measures etc) and the occurrence of several major chronic diseases. We are examining associations of environmental/modifiable risk factors with several cancer sites (e.g., breast, colon, rectum, endometrium, ovary, and renal cell cancer), myocardial infarction, stroke, osteoporosis, cataracts, as well as death causes. All these degenerative diseases appear to have some risk factors in common; therefore the same information about different lifestyle exposures is relevant for studying the etiology of the above mentioned as well as other chronic diseases.
The general rationale behind this longitudinal cohort is that prospectively collected exposure information is not influenced by differential recall and selection biases, which might be a problem in case-control studies. By updating exposure data on participants in the cohort, it is possible to take into account the changes in lifestyle factors which might influence estimates of the risks of different diseases. In our methodological study of the stability of food consumption over a period of 1-7 years, we observed that correlations between two dietary questionnaires decreased successively on average from 0.7 to 0.4 over 7 years. These findings underscore the importance to update exposure information, which we hope to do in the near future.
Complete and inexpensive follow-up of the cohorts is obtained through record linkages to the nationwide Cancer Register, the In-Patient Register, and the Death and Population Register. The possibility of such record linkages in Sweden to high quality registers makes our study unique in an international comparison.
Participation of the SMC together with other cohorts in the Pooling Project on Diet and Cancer at Harvard Medical School enhances the opportunity to compute relatively precise estimates of risks for common cancers and to study even rare outcomes. Moreover, it facilitates the study of potential interactions, e.g. between nutrients and smoking, which otherwise are difficult to study due to lack of statistical power in individual studies.
Establishment of the Swedish Mammography Cohort (SMC)
From 1987 to 1990, all women who lived in the Uppsala County of central Sweden and were born between 1914-1948 and all women who lived in the adjacent Västmanland County and were born between 1917-1948 received an invitation by mail to participate in a mammography screening program. A total of 66,651 women returned a completed questionnaire on diet, weight, height, parity, and education.
In 1997, a follow-up questionnaire was sent to all cohort members who were still living in the study area; the follow-up questionnaire was extended to include information on physical activity, medical history, age at menarche, history of oral contraceptive use, age at menopause, postmenopausal hormone use, and lifestyle factors such as, cigarette smoking history, and use of dietary supplements.
We intend to collect DNA in the SMC. Availability of DNA in the cohort will allow investigations of genetic susceptibility and gene*diet/environment interactions. Such studies will help to identify specific characteristics of subjects at higher risk for different chronic diseases and will facilitate more individually tailored preventive recommendations.
Ultimately, we hope to get more insight into how diet and lifestyle interact with genetic factors to influence the risk of chronic diseases. With such evidence-based knowledge, we may be able, through recommendations of dietary and lifestyle changes, to reduce the burden of major chronic diseases both at an individual level and in a population as a whole.