The main article I read was from an English Academic, drawing on lots of data, fair point we should check the sources of all these things.
It's just a theory at the moment, but one that makes intuitive sense - that lack of sunlight leads to detiorating health.
You're right in saying that there are other possible interpretations!
I agree that the lack of sunlight can have a powerful effect on us. This is bourne out through the studies on suicide rates.
The further north we are on the planet the higher the incidence of suicide so it isn't much of a jump to think that it has other major health impacts.
Source
Anything that gets people up and out is a good idea. There is a tendency in northern climes to spend a lot of time indoors.
The allergies definitely feel much more prevalent these days. Someone having a peanut allegy was very rare and novel idea not so long ago?
Guyana seems like an interesting place?