Study finds lack of sleep linked to high blood pressure. How much sleep is enough?

You’ve probably heard the widely-held belief that everyone needs eight hours of sleep a night for optimal health. But does this one-size-fits-all rule actually apply to everyone?

Sleep is crucial for mental and physical functioning. However, sleeping eight hours a night isn’t attainable for everyone. Sometimes the constraints of life, work, kids, and smartphones get in the way.

In reality, many people sleep less than eight hours a night, and some sleep more. Where does the “eight-hour rule” come from and does the average person actually need to sleep eight hours a night?

We spoke to experts about how much sleep people need, the effects of sleep deprivation, and tips to get a better night’s sleep.

Is 8 hours of sleep enough?

The eight-hour “rule” is actually more of a medical myth, Shelby Harris, Psy.D., a clinical psychologist specializing in sleep medicine and the director of sleep health at Sleepopolis, tells TODAY.com. So where does it come from and why is it so popular?

“It’s not actually that everyone needs eight hours. It’s that most people need between seven and nine. … That’s where it comes from,” she adds.

Healthy adults need to sleep at least seven hours a night on a regular basis for optimal health, according to the American Academy of Sleep Medicine. So for most people, eight hours is enough — but it isn’t necessary for everyone.

Sleep needs vary throughout a person’s lifetime and based on other factors like underlying health. Generally, experts recommend target ranges for each age group. For adults, it’s seven to nine hours of sleep per 24-hour period, but for children it’s much longer.

These recommendations come from large population studies looking at how much sleep people need, Dr. Molly Atwood, Ph.D., assistant professor of psychiatry and behavioral sciences at Johns Hopkins Medicine, tells TODAY.com.

A person’s sleep need is the number of hours they would sleep naturally — without any external constraints or alarm clocks — in order to wake up feeling rested and function the next day. If you get enough sleep at night, you’ll generally feel alert and won’t feel the urge to doze off throughout the day.

The normal distribution of sleep needs for adults looks like a bell-shaped curve, with the vast majority falling somewhere between seven to nine hours, says Atwood. However, there are people on either side of the median and extreme outliers.

“It really does depend on the person,” says Atwood. Some people only need six and a half hours of sleep every night, Atwood adds, whereas others may need more than nine hours to feel rested and function the next day.

Good sleep quality and a consistent sleep schedule — going to bed and waking up around the time every day — are also important.

When we sleep, the body cycles through four different stages of sleep, which are broken down into REM (rapid eye movement) sleep and non-REM sleep, Dr. Andrew Varga, a neuroscientist and physician at the Mount Sinai Integrative Sleep Center, tells TODAY.com.

Most people go through three to five cycles a night, with the duration of REM sleep getting longer each subsequent cycle later in the night, says Varga. This is referred to as the body’s “sleep architecture.”

Disrupted or abnormal sleep architecture can worsen the quality of sleep and over time, lead to sleep deprivation, the experts note. Sleep disorders like insomnia or sleep apnea, stress, and underlying health conditions can all affect sleep quality, says Harris.

Sleeping less than 8 hours a night

Seven hours of sleep is enough for most healthy adults. However, regularly sleeping less than seven hours a night is associated with adverse health outcomes, according to the AASM. While some people may find they can function on six hours of sleep, seven is the minimum number recommended by experts for optimal health.

The relationship between sleep duration and morbidity and mortality has been well-studied, says Atwood.

“What we typically see is that when you go below six or seven hours of sleep, you start seeing a stronger association between sleep and health problems or death,” says Atwood. The further you go below seven hours on a regular basis, the higher the risk.

A small percentage of people can sleep less than six hours a night and function normally without any adverse consequences. These so-called “short-sleepers” have a rare genetic mutation that allows them to sleep less than the average person, TODAY.com previously reported. But short-sleepers only make up a tiny subset of the population.

Most people who routinely sleep six or less hours a night will experience negative side effects the following day and have an increased risk of other health conditions in the long-term.

Health effects of sleep deprivation

We all have sleepless nights from time to time, and it’s usually possible to catch up after a few days of sleeping the usual amount you need, the experts note.

When you consistently sleep too little without catching up, it can lead to sleep deprivation — which has a number of consequences. “Sleep is important for pretty much every system in your body,” says Atwood.

In the short-term, sleeping well below the amount you need can cause deficits in cognitive functioning. The following day, people may experience delays in reaction time, poorer working memory, and difficulty paying attention, Varga notes.

In addition to feeling drowsy and tired, people may notice their mood is affected after a night of too little sleep. “It might be a bit harder to regulate your emotions and you might feel more irritable or down,” says Atwood.

In the long-term, chronic sleep deprivation increases the risk of cardiovascular problems, including heart disease, heart attack and stroke, Atwood says.

Research has shown that people who habitually sleep less than six hours a night also have a higher incidence of high blood pressure, kidney disease and diabetes, according to the experts. Sleep deprivation can also impact the immune system and affect metabolic functioning.

“There’s more and more data coming out that it can increase your risk of cognitive issues as you get older, such as dementia,” Atwood adds.

Chronic sleep deprivation is also associated with an increased risk of mental health problems including depression, bipolar disorder, and anxiety, TODAY.com previously reported. “If you’re sleep deprived after a trauma, this increases the risk of PTSD,” says Atwood.

How much sleep do you need?

The amount of sleep a person needs changes throughout different stages of life, and individual sleep needs can vary depending on factors such as genetics, underlying health, and their environment.

According to the latest AASM recommendations, the following age groups need this much sleep on a regular basis:

• Infants (4 to 12 months) need 12 to 16 hours, including naps
• Children (1 to 2 years) need 11 to 14 hours, including naps
• Children (3 to 5 years) need 10 to 13 hours, including naps
• Children (6 to 12 years) need 9 to 12 hours
• Teenagers (13 to 18 years) need 8 to 10 hours
• Adults need 7 or more hours

Besides sleeping the recommended amount, you know you are getting enough sleep if you wake up feeling rested and refreshed, and you’re able to function throughout the day without feeling an overwhelming drive to sleep, says Varga.

It’s normal to feel a bit groggy right after waking up, says Atwood. but if this fatigue persists and you find yourself wanting to doze off the entire day, you’re probably sleep deprived, she adds.

If you’re getting the recommended seven to nine hours of sleep a night and still feeling sleepy or tired, this could be a sign of poor sleep quality, according to the U.S. Centers for Disease Control and Prevention. Other signs include waking up throughout the night, snoring, and nighttime breathing difficulties.

Getting enough sleep every night is not always easy, the experts acknowledge. Life often gets in the way. Work obligations, school, parenting, lifestyle choices, and poor sleep hygiene are all common reasons why people do not get enough sleep, says Harris.

One-third of adults in the United States report that they usually get less than the recommended amount of sleep, per the CDC.

Tips to get more sleep

If you feel like you are not getting enough sleep or want to take steps to improve your sleep hygiene, the experts recommend taking the following steps:

• Create a wind-down routine every night.
• Make your sleeping environment comfortable, quiet, and dark.
• Avoid screens for 30 minutes to one hour before bedtime.
• Go to bed and wake up around the same time every day.
• Exercise regularly.
• Limit caffeine intake.
• Cut down on alcohol.
• Avoid taking naps too close to bedtime.

If you’re taking steps to improve sleep hygiene and still find yourself struggling to get enough sleep most nights, the experts recommend talking to a doctor or a sleep medicine expert.

This article was originally published on TODAY.com