One theory is that contagious yawning is related to empathy, and that people with higher levels of empathy yawn more often when someone else yawns, compared to people with lower levels of empathy or those with a mental disorder.
There was one exception, researchers said. A more recent clinical trial in China found that folic acid supplements helped curb participants' risk of stroke.
Two years ago, the American Diabetes Association asked Congress to hold hearings to determine why the cost of insulin was skyrocketing.
There was a 65% higher death rate for people who regularly slept less than 5 hours on all nights, compared with people who regularly slept 6 to 7 hours per night.
