For humans, a nightly doze plays an important role in health: It enables people to think clearly, function effectively and provides an opportunity for the brain to wash itself.

Most adults require between seven and nine hours of sleep per night, according to the National Sleep Foundation, yet some people have as little as five or six. Former U.S. president Barack Obama, for example, admitted to sleeping for as few as five hours per night during his presidency, while Margaret Thatcher, the former prime minister of the United Kingdom, claimed she only needed to get her head down for four hours each night.

It's been suggested that such individuals could have "short sleeper syndrome" — a condition in which people can achieve the same level of rest as a conventional sleeper but in a shorter period of time.

But does short sleeper syndrome really exist? Is it possible for a person to have less than the recommended amount of sleep without impacting health and wellbeing?

What is short sleeper syndrome?

"Short sleeper syndrome is experienced by people who normally have short sleep duration during the night but don't suffer any adverse effects of excessive sleepiness, cognitive impairment or lower mood during the day," he said. "That short amount of sleep [six hours or fewer, according to the Sleep Foundation] is sufficient for their own personal physiology." In other words, short sleepers feel bright and awake even with less sleep than is recommended.