Logical_Dot
There is a bit loophole here, first hokage died because of ashura chakra. He got disease, in sasuke retsuden. Naruto also got the same disease it was because of the abundant of yang chakra being used. He and 2nd hokage are not poisoned by daimyo.
I forgot he got sick before or after marriage. But for sure is before sasuke married sakura, because sakura followed sasuke to find cure.
ZoroTraineeWriter:The conclusion is he got sick because he overused his power which is Asura Chakra. Naruto got sick when he was still young before marriage because he used too much of his chakra during ninja world war 4 Hashirama got sick after he fought with madara last battle. He overused his chakra. Naruto was saved because sasuke went to the village where hagoromo loves, there are record of his disease so Konoha manage to make cure for Naruto. Hashirama got assasinated or poisoned is impossible because without a seal he can heal his injury. So the overused of chakra make his body sick