Published: 01-03-2017 15:39 | Updated: 06-03-2017 09:55

“Without you there would be no research”

What is a cohort?
Researchers call a group of individuals with certain shared characteristics who take part in a major study a cohort. By following a cohort over a long period of time or comparing different cohorts, researchers can draw conclusions about, for example, how and why diseases develop in different groups.

A group of women in Västmanland and Uppsala Counties have made possible much of the Swedish research on lifestyle, diet and diseases. The Swedish Mammography Cohort turns 30 today, 1 March.

Hello there, Alicja Wolk, Professor of Nutritional Epidemiology at the Institute of Environmental Medicine and responsible for the Swedish Mammography Cohort. How did the Swedish Mammography Cohort start?

“On 1 March 1987 all women between the ages of 40 and 74 in Västmanland and Uppsala Counties began to be invited to undergo a mammography and to answer a questionnaire about their diet, weight, height, education level and family history of breast cancer. Approximately 66,000 women chose to take part. Since then, the women have been followed up with new questionnaires every ten years. A sub-group of approximately 7,000 women have also taken part in clinical investigations, including bone density measurements and giving samples of fatty tissue, blood, urine and faeces.”

How important have these women been for the research?

“It is unusual to be able to follow this many individuals for such a long time so it’s a real goldmine for the research. By comparing the questionnaire responses and test results with information about the women’s illnesses in national health registers we’ve learned a great deal about how diet, lifestyle and genes affect diseases like different forms of cancer, cardiac infarction, stroke, osteoporosis and diabetes. We at Karolinska Institutet currently have responsibility for the register but it is available to all researchers and is the basis for many research collaborations.

What research findings have been the most significant?

About 500 studies have been published on these women so there is a lot to choose between. Personally I think it was interesting to be able to show that too much vitamin A is harmful to bone health. Many researchers doubted it at first but it has later been confirmed in other studies.

Was it difficult to get the women to participate?

“No, we’ve always had very high participation. When the women were first invited to mammography scans, 94 per cent chose to take part and between 70 and 80 per cent of those women have then answered the questionnaires we’ve sent out over the years. When similar studies begin nowadays participation unfortunately tends to be low, not seldom around 10-15 per cent.”

Why do you think that is?

“It might partly be a generation issue, it might be more difficult to get messages across today because people have so many to deal with. I also think that the women have felt that it is easy to take part and that they get something back. In the early days, a mammography bus visited the different areas so that the women wouldn’t need to travel long distances, and they have been given feedback if their test results show anything abnormal. We’ve also limited the length of the questionnaires so that it doesn’t feel like such very hard work to answer them.”

Will the cohort live to be a hundred?

“Some of the women have passed the hundred mark. The oldest was 103 according to our latest information. But the answer is no, the cohort has no inflow of new individuals. However, we continue to collect new data on these women, we are inviting them to clinical examinations in Uppsala and Västerås and we plan to send a new questionnaire to all of them in 2018. The Mammography Cohort has a "twin-cohort" of about 50 000 Swedish men. Together they contain many married couples and it would be very interesting to begin a new cohort for the next generation that contains these people’s children, grandchildren and even great-grandchildren. We’re currently looking at if it can be done.”

What would you like to say to all the women who have taken part over the years?

“A big thank you! The results of the research are of benefit to all women in Sweden and in the world, and without you there would quite simply be no research.