Thanks so much for your questions. It could be a circulation problem or an "atrophy of the soft tissue" problem. Women that wear high heels are known to have the balls of the feet some sort of numbness by the feet position when wearing high heels (not all of them).
I would recommned to improve circulation to your feet but also to focus in the soft tissue of the balls of your feet (getting it stronger)
Try this exercise:
From a standing position place a sock on the floor and try pick it up with your toes and bring it to your hand, do it ten times, then change to the other foot
Check this article: Pain in the Ball of the Foot (Metatarsalgia) http://www.merckmanuals.com/home/bone_joint_and_muscle_disorders/foot_problems/pain_in_the_ball_of_the_foot_metatarsalgia.html