Clipless and now numb toe - why?

[BikingAt50]

I was told that because bike shoes are pretty flat inside, that your foot doesn't have real support, so...numb toes.

That's true. I recently read that since cycle shoes are so flat and ungiving (non flex), that your toes vibrate. This causes tingling and numbness. This book suggest inner soles in the toe area to reduce vibrations. It also warns against tightening shoes too tight.