When it comes to sleep, anything less that six hours can hamper your ability to focus on minor tasks even if you feel rested.
Researchers from Brigham and Women's Hospital found often times people do not realize the effects of lack of sleep because they feel they are alert.
However, participants of the study were unable to perform simple tasks and did not do very well on memory tests.
For analysis, the team allowed nine people only 4.67 hours of sleep and were awake for 15.33 hours for 32 days.
Even though the participants were impaired because of chronic sleep restriction, they did not notice it.
"If somebody is routinely awake for more than 18 hours daily, then they are also routinely sleeping for less than six hours daily," senior author Doctor Elizabeth Klerman, from the hospital's Division of Sleep and Circadian Disorders, is quoted as saying by the Daily Mail.
"Therefore, it was unknown whether any decline in vigilance or other functions was due to the extended wakefulness or restricted sleep.
"We found that chronic short sleep duration, even without extended wakefulness, resulted in vigilant performance impairments."
Researchers urge people to make sleep a priority.
The findings are published in the journal PNAS....