correlation does not indicate causation. there could be a genetic component that varies by latitude. Ever notice blond hair gets rarer as you go towards the equator?
The solution for celiac is to never ingest wheat, barley or rye. The solution for Tropical spru is to relocate to an area without spru ~ usually further North.
Still, spru can be moderated with the administration of a number of anti-biotics. Cutting out wheat, barley and rye has only a modest benefit.
There is a latitude gradient involved in both conditions ~ probably not as pronounced as with the diseases discussed in these articles, but it's there.