Why Do Different People Need Different Amounts of Sleep?

How much sleep do we need? It's a fundamental question about a basic human function we've been practising for millennia, but there's still no simple answer. In recent years, scientific advances have suggested that it may in fact be different for each of us; genetics might play as much of a role in our sleep requirements as light, alarm clocks, and Red Bull consumption.

"I suppose the rule of thumb in adults is about seven to eight hours, but is that based on any really solid science? I would sort of say not," said Russell Foster, professor of circadian neuroscience and head of the Sleep and Circadian Neuroscience Institute at the University of Oxford. He pointed out that before industrialised times, natural light played a larger role in our waking and sleeping times, and people would often refer to their "first and second sleep."

But now we've hacked darkness with electricity, around eight hours is the general consensus; last year, the US National Sleep Foundation (NSF) suggested adults aged 18-64 should get 7-9 hours in its updated recommended sleep times.

Interestingly, however, the NSF researchers introduced a new category beyond their recommended figures called "may be appropriate," to account for the variation now recognised between individuals. Taking these values into consideration, the Foundation suggests anywhere from six hours to 11 hours of sleep per night for individuals between the ages of 18 and 25 may be suitable, or six hours to 10 hours for those between the ages of 26 and 64. One person's power nap, it seems, is another's extended lie-in.

Why the discrepancy? Aside from social constraints like having to get up early for a commute, Foster says there are two main biological factors that affect an individual's sleep needs: the circadian clock (often referred to as the biological clock) and the sleep "homeostat." Foster described the latter as a kind of internal egg timer for sleepiness. "The longer you've been awake, the greater the build-up of sleep pressure, the greater the need for sleep," he said. "And when you're asleep that sleep pressure dissipates and you feel less tired."

But as the sleep pressure builds through the day and you get more and more tired, you don't usually fall asleep when you're not supposed to because the biological clock effectively provides a timestamp for when sleep is a good idea (i.e. at night). You can see this at work when you travel to a different timezone and your sleep pattern adjusts to the new light cycle.

These biological processes vary from person to person owing to environmental factors (such as light exposure) and genetics. And this is why our sleep schedules show such variation.

"We now know there are key genes associated with the biological processes, and subtle changes within those genes can make you more of a morning person who likes to go to bed early and get up early or an evening person—you go to bed late and get up late," said Foster.

Most of us tend to be evening people, but there are drawbacks to both ranges. If you're a night owl, then getting up for work early can interfere with your natural sleep preferences; if you're a morning lark, then social obligations tend to get in the way.

"Morningness" and "eveningness" can run in families, but there's a lot of room for variation. The process of protein synthesis and degradation in the relevant genes allows for many points at which subtle changes could influence an individual's sleep pattern.

"The rate at which you turn the genes on, the rate at which the genes make the proteins, the rate at which the proteins make complexes, the rate at which they enter the nucleus, the rate at which they turn off their own genes, and the rate at which those protein complexes are degraded, actually make a 24-hour oscillation," explained Foster.

Tweaks at any point in that process could affect your genetic predisposition to like early nights or lazy mornings.

The environment can modify your sleep preferences but there's no easy hack—you can't change your genes (yet). That said, your sleeping pattern will change naturally with age, which is also reflected in the National Sleep Foundation recommendations: it suggests 14-17 hours of shuteye a day for newborn babies and only 7-8 hours for over-65s.

But Foster said it's about more than simple duration. Teens and people in their early 20s genuinely do want to go to bed later and get up later too, something researchers propose might be to do with changing hormones. "On average, there's about a two-hour difference in preferred sleep times of somebody in their late teens/early twenties to somebody in their late 50s [or] early 60s," he said. "So asking a teenager to get up at 7 o' clock in the morning is the equivalent of asking a 55-year-old to get up at five in the morning."

At the end of the day, the best way to gauge how much sleep you need is to listen to your own body. Do you rely on an alarm clock to wake up? Do you take a long time to feel awake? Are you dependent on caffeinated drinks to keep you focused during the day? Do you lack empathy? Are you overly impulsive—do you find yourself running a lot of amber traffic lights, for instance? All these could be signs that you're not getting enough sleep.

And that, we know today, is bad. Foster said he thought the understanding of the importance of sleep was "one of the great triumphs of modern neuroscience," and that society was moving away from the all-nighter culture of the 80s to respect the need for sleep. "It's not an indulgence or a luxury, it's not a time when the brain and body are doing nothing," he said. "It's a critical part of our biology."

You'll Sleep When You're Dead is Motherboard's exploration of the future of sleep. Read more stories.