This is why "non-essential" and "essential" are misleading terms, and should be replaced by "non-restrictive" and "restrictive".

The clause "in Sweden and in Finland" is a restrictive clause because it answers the question "which recent studies?" (unless you believe that there was only one set of recent studies) and thus there should be no comma. The fact that you can remove the clause from the sentence without making it non-grammatical does not change the fact that this is a restrictive clause.

Finally, I believe the sentence reads much better with the fourth comma than without it.

This is why "non-essential" and "essential" are misleading terms, and should be replaced by "non-restrictive" and "restrictive".

The clause "in Sweden and in Finland" is a restrictive clause because it addresses the question "which recent studies?" (unless you believe that there was only one set of recent studies) and thus there should be no comma. The fact that you can remove the clause from the sentence without making it nonsensical does not change the fact that this is a restrictive clause.

Finally, I believe the sentence reads much better with the fourth comma than without it.