Does running make your boobs smaller?

okay so im a very small girl, 100 lbs and like 5'3. I like to walk/jog on my treadmill for 3 miles every day. I heard this makes your breasts smaller? is this true? I run mainly because I want a flat stomach and smaller thighs, I do 100 sit ups after running too. I don't eat a whole lot, but I'm not anorexic.