We all know the basic, 8-hour-a-night sleep prescription. That’s the number that gets tossed around a lot, as the amount of sleep we’re all supposed to be shooting for every night.

Like with so much about sleep, the reality on the ground is more complex. Let’s look at a few of the most important factors that affect our individual needs for sleep.

Age

Sleep needs change over our lifetimes, most drastically during the developmental years of childhood and adolescence. Any parent knows newborns need a lot of sleep throughout the day and night. But right through their high-school years, children and teens need more sleep than adults to, to help fuel all the physiological growth and development they’re undergoing.

The National Sleep Foundation recommends these amounts of sleep for kids and teens:

Infants: 12-15 hours

Toddlers: 11-14 hours

3-5-year-olds: 11-14 hours

6-13-year-olds: 9-11 hours

14-18-year-olds: 8-10 hours

What happens when we get to adulthood? Our sleep needs settle out, and essentially remain the same throughout our adult lives. Contrary to what people often think, scientists and sleep experts say we don’t need less sleep during older adulthood. Instead, in order to function and feel at our best, we need about the same amount of sleep we did when we were in our 30s, 40s, or 50s.

The National Sleep Foundation recommends these sleep amounts for adults:

Young adults, ages 18-25: 7-9 hours a night

Adults, ages 26-64: 7-9 hours a night

Older adults, 65+: 7-8 hours a night

Genes

Even within our own families, we all probably see different sleep needs and sleep habits that seem deeply ingrained. I like to get out of bed very early, and I’m happy when my head hits the pillow by 9 or 9:30 p.m. On less than 7.5 hours of sleep, I’m apt to feel a little sluggish, mentally and physically. My husband likes to stay up later than I do, and for him, 7 hours a night is just about perfect.

Our genetics play a role in establishing our individual needs for sleep. This is why the guidelines above are only guidelines, because we’re all a bit different, when it comes to the “right” amount of sleep.

Our genes affect how much we sleep, and also the preferred timing of our sleep. Genetics plays a big part in determining whether we’re early birds, night owls, or somewhere in between. (These preferences are known as chronotypes, and they affect not only our sleep-wake cycles, but the timing of plenty of other physiological functions, from digestion and cognition to daily cycles of mood and energy.)

Scientists also think our genes are a factor in our risk for snoring and other forms of sleep-disordered breathing including sleep apnea.

Of course, we can’t change our genes, but we can work to become more aware of our own, innate preferences, and do our best to tailor our sleep schedules to meet them.

Sleep debt

This is a common factor in our need for sleep, and it’s a bit different for everyone. Sleep debt is the deficit between the amount of sleep our bodies need, and the amount we’re actually getting. When we don’t get enough sleep to meet our individual needs, our sleep debt grows—like the unpaid balance on a credit card. Many of us carry a sleep debt from week to week, and month to month. The only way to erase a sleep debt is by making up the sleep we’ve missed out on. When you are carrying around a sleep debt, you’re in need of additional sleep beyond your typical “right” amount.

The National Sleep Foundation has tips for helping to pay down a sleep debt. Their main advice? Don’t try to make up lost sleep all at once. Slow and steady is the better route to making up lost sleep.

Written by Caitlin Reynolds

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