The European Biological Rhythms Society (EBRS), European Sleep Research Society (ESRS), and Society for Research on Biological Rhythms (SRBR) put out a joint statement that recommends all-year Standard Time in the EU:

* https://esrs.eu/wp-content/uploads/2019/03/To_the_EU_Commiss...

I would hazard to guess some of those folks have looked at data for northern Europe and took it into account when forming their conclusions.