Cats don't see any reason to keep up with the tight schedules humans observe. They sleep when they want to, play when they want to, and stare at you judgmentally when they want to. A cat sees no reason why you should sleep so many hours in a row when you should be taking cat naps instead. Yeah, cats can adjust to a human's schedule, but many will lose their patience and demand their human's attention very early in the morning. Why is that?
It's very possible that you have taught the cat to wake you up early by giving it what it wants. If you get up and feed your cat at 4AM, hoping to go back to sleep for another couple of hours, the cat has learned that such behavior will be rewarded. Ignoring the cat in order to un-teach that lesson may take a few difficult mornings, but it will eventually be worth the effort.
If a learned response is not the problem, you'll need to find out what is causing your cat to wake you up early. There are three common reasons: they are hungry, they don't have a routine, or they aren't using up enough energy in the daytime. An article at The Conversation goes through the reasons why these things will cause an early wake up, and what you can do about them. -via Fark