Nurses working shift work for six years or longer are 1.5 times more likely to have coronary heart disease than non-shift workers. Perhaps, for example, nurses on shift work have a poorer diet that causes heart disease. One way to find out is to control everything, but this wouldn't be possible with humans. However, in controlled laboratory studies using rats, sleep deprivation has been shown to cause loss of weight, lowered body temperatures, illness, and eventually, death. Fortunately, microsleep keeps this from happening to humans.
Humans can and do get by on less than eight hours of sleep.
Jerry, my college friend, hit the wall during exams. Although he thought that he had written a brilliant examination, the instructor flunked him. What Jerry thought was a brilliantly written examination consisted of pages full of illegible scribbles.