Results of a study of more than 95,000 adults in the UK show that six to eight hours of daily sleep was associated with the lowest risk of health problems during the follow-up period. In this study, longer REM sleep duration was associated with a lower risk of 83 diseases and conditions, and longer deep sleep duration was associated with a lower risk of seven conditions, but a causal relationship was not established.
Most scientists believe sleep has multiple roles, including memory consolidation, clearing metabolic waste from the brain, providing an opportunity for rest and repair of the gut environment and its microbes, and supporting immune system health. Whatever sleep’s functions are, scientists know that quality sleep is vital for long-term health. In fact, we know we need sleep and that sleep matters, but its precise functions are not yet fully clear. Now a new study has examined the relationship between sleep and disease-related outcomes over nearly a decade of follow-up.
According to Medical News Today, researchers found that longer REM sleep duration, the rapid eye movement stage often associated with dreaming, was linked to lower risk of 83 conditions, and longer deep sleep was linked to lower risk of seven conditions.
Previous research has linked short sleep duration with disease and increased risk of death, but many of those studies relied on self-reported sleep duration-that is, participants reporting how many hours they slept. This method has limitations because people may not recall time accurately and do not always know exactly when they fell asleep or woke during the night. Moreover, self-reported sleep duration does not indicate how long a person spent in each sleep stage.
In the new study published in the journal PLOS Medicine, scientists used wrist-worn motion-recording devices to obtain more precise information about participants’ sleep stages, duration, and sleep pattern irregularity.
In total, data from 95,559 people in the UK with a mean age of 56.2 years were analyzed. Participants wore the motion-recording device on their wrist for one week to assess the amount and quality of their sleep. They were then followed for a mean of 8.9 years until the occurrence of a disease or death.
Researchers found that longer REM sleep duration at the start of the study was associated with lower risk of more than 80 conditions and diseases, including heart failure, hypertension, atrial fibrillation (a type of heart rhythm disorder), ischemic heart disease (due to reduced blood flow to the heart muscle), parkinsonism (a set of movement symptoms resembling Parkinson’s disease), multiple sclerosis, and various forms of dementia.
Meanwhile, longer deep sleep duration was associated with lower risk of seven diseases and conditions, including type 2 diabetes, major depressive disorder, sleep apnea, and Parkinson’s disease.
However, the authors emphasize that the observed associations with some of these diseases may be due to reverse causation. Depression is a good example: sleep disturbance is a common symptom of depression. Thus, rather than irregular sleep causing depression, depression may have made sleep irregular.
In contrast to deep sleep, longer light sleep duration-which can indicate poorer sleep quality-was associated with higher risk of some conditions such as major depressive disorder, but was also associated with lower risk of some other conditions, including heart failure and cellulitis (a type of skin and subcutaneous tissue infection).
Scientists also examined an index called wake after sleep onset (WASO). This index represents the total time a person is awake during the night after initially falling asleep. In other words, it is one marker of sleep fragmentation. Higher values of this index were associated with increased risk of six conditions including substance dependence, alcohol misuse, and osteoarthritis.
Researchers also examined irregular sleep patterns and found these patterns were associated with increased risk of abdominal pain, anxiety, and major depressive disorder.
Overall, longer total sleep duration was associated with lower risk of at least 50 conditions, including protein-energy malnutrition, acidosis (increased acidity of the blood), and type 2 diabetes.
The researchers concluded overall that six to eight hours of sleep was associated with the lowest risk in the study’s data; a range that differs slightly from the more commonly recommended seven to nine hours.
Experts’ recommendations for better sleep
For those who find it hard to get enough sleep, these results may be worrying. Therefore, some practical recommendations from experts are compiled here.
First, try to keep your wake-up time consistent. Waking up at roughly the same time each day helps the brain set a pattern for awake time and the body’s need for sleep. This routine should continue on weekends. Sleeping a few extra hours after a late-night event may feel pleasant, but in practice it shifts the sleep schedule and makes it harder for the brain to fall asleep the next night.
Exposure to daylight shortly after waking also helps consolidate this routine.
The second recommendation is not to struggle to sleep while in bed. If a person repeatedly goes to bed without falling asleep and becomes anxious about sleeping, the brain may associate the bed with failure and alertness. In such a situation, get out of bed for about 15 to 20 minutes, go to a quiet, dimly lit room, and do a calming activity away from distractions. When you feel sleepy again, return to bed.
A quiet, dark, cool bedroom with a temperature of around 18 to 21 degrees Celsius is also very effective. For sleep onset and maintenance, core body temperature should drop.
Having a regular pre-sleep routine is also important. Doing relaxing activities in low light for at least 30 to 60 minutes before bed helps the brain and body calm down and prepare for sleep. This routine can include light reading, listening to calm music, taking a warm bath, meditation, or deep-breathing exercises. It is better to avoid stimulating activities such as watching media content or using your phone.
Stopping caffeine intake after 3 p.m. and avoiding heavy meals within two hours of bedtime are also recommended.
At least 30 minutes of daily exercise that raises the heart rate is also emphasized. This helps use up excess cortisol, a hormone that can increase alertness and reduce sleep quality.