"There's an association between (poor, inadequate) sleep and obesity," said Dr. Joseph Ojile, head of the Clayton Sleep Institute.

Once you're obese, you're more prone to sleep apnea, the collapse of the upper windpipe which interrupts breathing during sleep. That's the vicious circle: sleep apnea can help cause obesity, and obesity can cause sleep apnea.

One of the first questions she asks her patients is how much sleep are they getting. "They look at me as if to say, 'Why are you asking that?' "