GetAsyncKeyState() very CPU heavy? Am I using it correctly?

I am using GetAsyncKeyState() in a simple pong game of mine to check if the user has pressed the arrow keys. I read online that you need to use this function a certain way however I found out that it is very CPU heavy (using 50% of my CPU!). This was rather disconcerting, however, after some playing around I found out that if I added a sleep(1); then the CPU usage went down to 0% and everything still worked fine. There must be a better way of using this function or at least a better way of lowering CPU usage.

Any help here would be much appreciated!

My Code:

while(true)
 {
     for(i = 8; i < 191; ++i)
     {
         if(GetAsyncKeyState(i) == -32767)
         {
             if(i == VK_LEFT)
                  // do stuff
             else if(i == VK_RIGHT)
                  // do stuff
             else if(i == VK_UP)
                  // do stuff
             else if(i == VK_DOWN)
                  // do stuff
         }
     }
     Sleep(1);
 }
 

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