Why do some people need more sleep than others?


wiseGEEK Writing Contest

Scientists have recently discovered that genetics may play a role in sleep dependence. A multidisciplinary group from England’s University of Surrey investigated the effects of a circadian-rhythm gene called period3 on sleep deprivation. Period3 has already been found to affect a person’s sleep habits and determines whether someone is a “night owl” or a “morning lark.” Now these scientists say that it also affects attention span, reaction time, and short-term memory after sleep deprivation.

Period3 comes in two variants, long and short, and everyone has two copies of the gene. The researchers, headed by Derk-Jan Dijk and Antonine Viola, studied 24 people, all of whom had either two longs or two shorts. First they deprived the group of sleep for 48 hours. Then they gave them tests that included pushing buttons after seeing light flashes and recalling lists of numbers.

The participants with long period3 genes had slower reaction times and more trouble remembering. The worst hours (for both groups, but particularly those with the long genes) were in the early morning, from four to eight am. These are the hours reported as most difficult for truck-drivers and shift workers, and also the hours when most sleep-deprivation-related accidents occur.

When the participants were finally allowed to sleep, those with the longer genes fell asleep after an average of eight minutes – less than half of the time averaged by those with short variants (18 minutes). Moreover, they remained in a deep sleep for one and a half times as long as the group with the short genes. This suggests that people with the long period3s have an innate need for more sleep, which leads to inferior performance when sleep is deprived.

Although this study suggests that sleep needs are genetic, the fact remains that our hectic 24/7 lifestyles lead to sleep deprivation across the board. Beyond making you feel tired, sleep deprivation can seriously impair health and mental ability. Risk for diseases – including heart disease, obesity, diabetes, and depression – increases when a person receives less than 6-7 hours a night. Sleep deprivation also impairs mental performance. A 2001 study showed that college students who slept more than nine hours a night had, on average, higher GPAs than those who slept for less than six hours. Obviously, this has significance beyond students' grades: anyone who has a job, hobby, or lifestyle that involves thinking (and who doesn't?) would be better off with a full night's sleep.

The long and the short of it: the verdict’s not completely out yet on the link between genetics and sleep, but it is clear that your body knows what it needs. It may be worth forgoing a few minutes of work to catch up on your sleep...and increase performance tomorrow.