In those with type 2 diabetes, insulin resistance builds up over time, and lifestyle factors may play a part.
Hanks first revealed his diagnosis in 2013 during an appearance on "The Tonight Show with David Letterman."
"I went to the doctor, and he said, 'You know those high blood sugar numbers you've been dealing with since you were 36? Well, you've graduated! You've got type 2 diabetes, young man,'" Hanks said.
In a 2016 interview with the Radio Times, he added: "I'm part of the lazy American generation that has blindly kept dancing through the party and now finds ourselves with a malady."
"I was heavy. You've seen me in movies, you know what I looked like. I was a total idiot," he continued.
"My doctor says if I can hit a target weight, I will not have type 2 diabetes anymore," he added.