Sleep and your body

How much sleep do I need by age?

Adults aged 18 to 64 need 7 to 9 hours of sleep a night, and adults over 65 need 7 to 8 hours⁵. Children and teenagers need more.

The American Academy of Sleep Medicine and the Sleep Research Society agree that adults need at least 7 hours. Regularly sleeping 6 hours or less is "inadequate to sustain health and safety in adults"¹.

If you want to know whether 6 hours can ever be enough, read 6 hours vs 8 hours: the myth and the reality.

Do Indians get enough sleep?

By the clock, Indians in big cities get enough sleep: India's Time Use Survey 2024 found an average of at least 7 hours a day in six big cities¹⁰. But those diaries count time asleep, not how well you slept.

People in Bengaluru, Mumbai and Pune slept over 8 hours. People in Delhi and Kolkata slept under 8¹⁰.

Men slept more than women in every one of those cities except Chennai¹⁰. In many homes, the person who locks up at night is the same person who makes the morning tea.

Time in bed is not the same as rest. A night broken by heat, a snoring partner or a child's cough can add up to 8 hours on paper and still leave you tired.

What are the stages of sleep?

Sleep has 4 stages: 3 stages of non-REM sleep (N1, N2, N3) and then REM sleep. Together they make one cycle of about 90 minutes, repeated 4 to 6 times a night².

REM sleep (rapid eye movement sleep) is the stage when most dreaming happens and the eyes move quickly under closed lids. Non-REM sleep is all the other sleep, from light to deep².

N1 is the doze between waking and sleep, 1 to 7 minutes. N2 is light, steady sleep and fills about half the night. N3 is deep sleep, the hardest to wake from. REM is about 25% of the night².

REM periods grow longer towards morning². So when the alarm cuts a night short, it mostly takes REM sleep.

Sleep may also clean the brain. In a study on mice, the space between brain cells grew by 60% during sleep, and a protein linked to Alzheimer's disease cleared faster¹¹.

That study was in mice. Scientists are still testing whether the same happens in people.

For more on each stage, read Different stages of sleep.

What is deep sleep, and how much do you need?

Deep sleep (stage N3) is when your body does much of its repair, and you get most of it early in the night². It comes in stretches of 20 to 40 minutes that shrink in later cycles².

Deep sleep supports recovery, growth and the immune system. It is also linked to memory².

REM sleep has its own job. It is essential for memory, learning and creativity². A student who sleeps after studying gives the brain time to store what was learned.

You cannot force deep sleep. What helps is enough hours at regular times, and a room cool and quiet enough that you stay asleep. Chapter 2 covers the room, the heat and the routine.

What happens to your body if you don't sleep enough?

If you don't sleep enough over months and years, the risk of heart disease, high blood pressure, stroke, high blood sugar, obesity and depression goes up. Common infections also become easier to catch³.

One late night does not do this. The risk comes from short sleep night after night.

Many Indians work night shifts, run family businesses late or care for a parent at night. If that is you, the numbers here are not a judgement. They are a reason to protect the sleep you can get.

Can lack of sleep make you gain weight?

Yes, lack of sleep can make you gain weight. It raises ghrelin, the hormone that makes you hungry, and lowers leptin, the hormone that tells you that you are full³.

That is one reason the fridge looks tempting after a late wedding or a long shift.

In a real-world trial, 80 adults who were overweight slept about 1.2 hours more a night. They then ate about 270 fewer calories a day, without being told to diet¹².

Weight and sleep also work the other way. Extra weight makes sleep apnoea more likely¹³. Sleep apnoea is when breathing stops again and again during sleep, which breaks it up¹⁴.

Can poor sleep cause high blood pressure, heart problems or diabetes?

Poor sleep is linked to high blood pressure, heart disease, stroke and type 2 diabetes³. The less you sleep, the higher the risk¹⁵¹⁶.

Across 16 studies of more than 1 million people, sleeping under 7 hours was linked to about a 7% higher risk of high blood pressure. Under 5 hours, the risk was about 11% higher¹⁵.

A UK study followed about 248,000 people for more than 12 years. Compared with 7 to 8 hours, sleeping 5 hours a night gave a 16% higher risk of type 2 diabetes. Sleeping 3 to 4 hours gave a 41% higher risk¹⁶.

For diabetes, a healthy diet did not cancel the extra risk¹⁶. In families where diabetes runs from grandparents to grandchildren, sleep belongs on the list next to food and walking.

Does sleep help your immune system?

Yes, sleep helps your immune system: people who sleep less catch colds more often and make fewer antibodies after a vaccine⁹¹⁷.

In a study, 164 volunteers were exposed to a cold virus. Those who slept under 6 hours were 4.2 times more likely to catch it, and those under 5 hours 4.5 times⁹.

In the monsoon, when a cold goes round the whole house, the person sleeping least is more likely to catch it⁹.

Sleeping under 6 hours around the time of a vaccine left people with fewer antibodies. The drop was about equal to 2 months of the protection fading. This came from 7 studies of flu and hepatitis A and B vaccines¹⁷.

If you have a vaccine due, try to sleep well on the nights before and after it.

Why do I wake up with back pain?

Waking up with back pain usually comes from the way you lie for hours: twisted, on your stomach, or on a surface that is too soft or too hard. Short sleep can also make pain worse.

Back pain is very common. In 2020, low back pain affected 619 million people in the world, and it is the single leading cause of disability⁷.

About 90% of low back pain is "non-specific". Non-specific back pain is pain with no single clear cause, such as an injury or a slipped disc⁷.

Pain and sleep pull on each other. In 13 studies of people with low back pain, about 6 in 10 also slept badly. The worse the pain, the more likely the poor sleep⁸.

The link runs both ways, but sleep is the stronger side. A poor night predicts more pain the next day more reliably than pain predicts a poor night⁴. So sleeping well is part of looking after a sore back.

Position matters too. In a small study of 53 adults, people who woke with neck pain spent more of the night in twisted positions than people without pain¹⁸.

A twisted position here means lying on your side with your top leg pulled forward over the bottom one, or lying on your stomach. Both turn the spine for long stretches¹⁸.

What is the best sleeping position for back pain?

The best sleeping position for back pain is on your side or your back, with pillows that keep your spine in line. Sleeping on your stomach is hardest on the back¹⁹²⁰.

A review of the research found that side lying was generally protective against waking back and neck pain. It also found there are not yet enough good studies to be sure¹⁹.

On your side, bend your knees slightly towards your chest and put a pillow between your knees. This keeps your spine, pelvis and hips in line²⁰.

On your back, put a pillow under your knees. This helps your back muscles relax and keeps the natural curve of your lower back. A small rolled towel under your waist can add support²⁰.

On your stomach, try a pillow under your hips and lower belly to take the strain off your back. Better still, try to sleep in another position²⁰.

In a shared bed or a room full of family, you may not have space to stretch out. A pillow between the knees takes no extra space.

Is it good to sleep on the floor for back pain?

Sleeping on the floor is not proven to help back pain. No good study has tested it, and in a large trial of surface firmness, the firmer surface did worse²¹.

Many Indians grow up hearing "sleep on something hard for your back". The research does not support that.

A Spanish trial followed 313 adults with long-term low back pain for 90 days. People who slept on a medium-firm surface had less pain lying in bed and less disability than people on a firm surface²¹.

Medium-firm means a surface that gives a little under your shoulders and hips but does not let them sink. A 2021 review of 39 studies came to the same answer: medium-firm surfaces gave better comfort, sleep and spinal alignment²².

Many families still sleep on a mat or a thin layer on the floor, especially in summer. If you wake without pain, there is no need to change. If you wake stiff, the floor may be too hard for your hips and shoulders.

What pillow height is right for neck pain?

The right pillow height for neck pain is the one that keeps your neck in line with your chest and back²⁰. On your side, that takes more height than on your back²³.

On your side, the pillow should fill the gap between your ear and the bed, so your head does not tilt down or up²³.

On your back, the pillow only fills the space under your head and neck, so it is lower²³.

There is no single right number. Single studies found about 7 to 10 cm most comfortable lying on the back, and about 10 cm on the side. A 2021 review says there is still no firm answer for either²³.

The shape and height of a pillow change how your neck lines up. In people with long-term neck pain, though, pillow design did not change how well they slept²⁴.

Neck pain is common: it affected 203 million people in the world in 2020²⁵. Cervical spondylosis is wear in the bones and discs of the neck. If you have it, the same idea holds: your neck should stay level, neither bent up nor dropped down.

Is loud snoring a sign of a problem?

Loud snoring can be a sign of sleep apnoea, especially with pauses, gasps or choking. Sleep apnoea is when the airway narrows or closes during sleep and breathing stops for a moment, again and again¹⁴.

About 11% of Indian adults may have obstructive sleep apnoea. That is about 10.4 crore people of working age, and about 4.7 crore of them may have it at a moderate or severe level⁶.

Men are more likely to have it than women: about 13% of men and 5% of women⁶.

You may not notice it yourself¹⁴. In a shared room or a joint family home, the person who notices is usually whoever sleeps nearby.

Sleep apnoea shows up in the day too. Signs include feeling very tired all day, finding it hard to focus, mood swings and waking with a headache¹⁴.

Weight plays a big part. About 60% of moderate to severe cases have been linked to obesity¹³. If you can't sleep for other reasons, Chapter 5 covers insomnia.