How is it that most of us need a restful eight hours of night but there are people who can get by with less – a lot less?

Sleep researchers call these indefatigable folks “short sleepers” -- people who can regularly get through the day on just a few hours of sleep and fare just fine.

Chronic sleep deprivation is known to impair our ability to learn and consolidate memories. But short sleepers seem to be able to perform as well as anyone else on cognitive tests and it remains a mystery why.

Dr. Andrew Lim, a sleep neurologist at Sunnybrook Health Sciences Centre in Toronto, says there’s much that remains unknown about what makes “short sleepers” tick.

“The average person probably needs about seven or more hours of sleep to function optimally. But there is a subset of the population who seem to be able to get by on six hours or less, without much in the way of consequences,” Lim told CTV News Channel Wednesday.

Lim is currently leading the Ontario Sleep Health Study, a research project to study the effects of sleep deprivation and sleep interruption on cognitive impairment and dementia. The aim is to better understand how exactly poor or fragmented sleep might lead to dementia later in life.

His team is currently recruiting 4,000 working-age Ontarians to provide DNA samples and wear an accelerometer to record their sleep patterns.

Lim is also hoping to identify the genes related to sleep and circadian rhythm, to better understand why “short sleeping” seems to run in families.

While there are some people who claim they have learned to get by on less shuteye, Lim believes we really can’t train ourselves to be short sleepers; we just have to be born that way.

“To a large extent, our sleep need is hard-wired in our genes. So you’re either a short sleeper or you’re not,” he says.

It’s estimated that approximately five per cent of the population needs nine hours of sleep a night or more; another five per cent need about 6 to 6.5 hours. Then there’s the one per cent who can get by with even less. The rest are in the seven to eight hours sleep category.

Some of the genes linked to short sleep have already been found; Lim’s team hopes to find more. The eventual aim is to develop genetic tests for short sleeping, he says.

“We may be able to better understand the underlying neurobiology and perhaps develop interventions based on that neurobiology to help people who are currently longer sleepers adapt to shorter sleep times. A pill for short sleep, sort of speak,” he said.