"Structurally and biochemically, the nervous systems of sensation seekers are different from those of other people," says Barry Smith, professor and associate chairman of the psychology department at the University of Maryland.
The physical sensations most people associate with fear and anxiety are interpreted as excitement by those who thrive on taking risks.
"The same people who enjoy racing are also likely to get involved in parachuting, acrobatic flying, downhill skiing, mountain climbing and other high-risk but non-competitive activities," says Smith.
"No question about it," says Dr. Barry Smith, a research psychologist at the University of Maryland.
"Up to five cups of coffee a day - or about 500 milligrams - and for some even more, is going to be perfectly fine," says Smith, a caffeine expert and director of the human-psychophysiology lab at the University of Maryland.
Like a pot of the black stuff on the tossing mess desk of a Navy warship, conventional wisdom has ebbed and flowed over the years on the merits of caffeine, Smith says.
"There have literally been thousands of studies done, and the drug has certainly had its ups and downs in terms of whether or not it's thought to be helpful," he says, "but the current research over the past 10 years suggests that there are no obvious lasting dangers and that, in fact, there may actually be some benefits."
However, he cautions that some people are more sensitive to caffeine than others.
Barry Smith, a professor in the psychology department at the University of Maryland and author of the upcoming book "Caffeine Consumption: Effects on Health and Behavior," said coffee can cause health problems.
"While caffeine itself has been established by much of the literature as neutral - not really good, not really bad - coffee itself is where the danger comes from," Smith said.