Toronto, Oct 11 (IANS): While lack of proper sleep has been known to affect health, a new study has showed that people who sleep less or more than an average of seven to eight hours per night are more likely to develop impairments in their mental skills.

The findings showed that sleep affected all adults equally.

The amount of sleep associated with highly functional cognitive behaviour was the same for everyone (seven to eight hours), regardless of age.

Also, the impairment associated with too little or too much sleep did not depend on the age of the participants, the researchers said.

"We found that the optimum amount of sleep to keep your brain performing its best is seven to eight hours every night and that corresponds to what the doctors will tell you need to keep your body in tip-top shape, as well," said lead author Conor Wild, Research Associate at the University of Western Ontario in Canada.

"We also found that people that slept more than that amount were equally impaired as those who slept too little," Wild added.

For the study, published in the journal SLEEP, the team examined more than 40,000 participants.

Nearly half of all participants reported typically sleeping less than 6.3 hours per night, about an hour less than the study's recommended amount.

Most participants who slept four hours or less performed as if they were almost nine years older.

Importantly, the participants' reasoning and verbal abilities were two of the actions most strongly affected by sleep while short-term memory performance was relatively unaffected.

On the other hand, even a single night's sleep can affect a person's ability to think. Participants who slept more than usual the night before participating in the study performed better than those who slept their usual amount or less, the researchers said.