It is specifically stated, numerous times, that the Uzumaki were known for their large chakra reserves, and strong bodies. Made them naturally adept at fuinjutsu, as well as increasing their average life span. It's also what made Kushina survive the Kyuuni extraction, when all other jinchuriki died. Also states their relation to the Senju, who were descendants of the Younger Son, and who received his strong body and chakra, while the Uchiha descend from the Older Son. They got his dojutsu, and it's also what makes the entire clan a bunch of whiney little sissy whores. Except for Itachi and Shisui. Somehow, Itachi and zshisui were born with a nice set of testicles, whereas the rest of his clan were born with a soft, pink vagina. Like Obito, Sasuke, Madara, Izuna, etc.