Jyrki is a certified clinical nutritionist and an adjunct professor of nutritional epidemiology. His main interest in research is the impact of dietary fatty acids and their food sources on the risk of major chronic diseases, mainly on cardiovascular diseases and type 2 diabetes. The other major topic of research interest is vitamin D.

For several years the main interest of research for him was the health effects of fish consumption and environmental contaminants in fish, but recently he has given more attention also to other dietary fatty acids and their food sources. The main study population for these investigations has been the KIHD cohort. During the recent years he has also expanded his field of research to vitamin D. In addition to the epidemiological research in the KIHD cohort, he is a co-principal investigator of the large Finnish Vitamin D Trial and a principal investigator of smaller vitamin D trials, such as VitDbol, which concentrate mainly on the molecular effects of vitamin D.