The most common cause of sleep talking is emotional stress. We (and by we, I mean the people I work for) treat many patients that talk in their sleep.
Unless your sleep talking involves violent outbursts or random screaming sessions, I wouldn't worry about it, and it's generally believed to be harmless.
If you want to reduce it, your best bet would be to stop sleeping only 4 hours per night and get on a normal sleep schedule. That usually helps to decrease the amount of talking to a minimum.
i talk in my sleep how can i be treated