Actually, what I would say is:
Have there been any studies regarding this and if so what were the conclusions?
Think about it this way. Consider the eggs in your fridge. Do you know how many there are? Are you sure there are any at all? Notice that even if we're accepting the possibility that there might just one (or none), the typical question to ask would be, "Are there any eggs in your fridge?" and not "Is there an egg in your fridge?"
Apart from that, when you're talking about research papers, we very often talk about "conclusions" in the plural form: "What were the conclusions of the study?" is far more common than "What was the conclusion of the study?", perhaps in part due to the possible dual meaning of the word "conclusion" in its singular form (you could also be asking about how the study ended).