How to live longer: is six hours sleep sufficient for longevity?

Maintaining the perfect balance of work, socialising and sleep can be challenging. However, sleep gives the body a chance to recover from the daily demands of modern life and should be prioritised. Studies have shown that, over time, sleep deprivation can increase the risk of developing chronic diseases like mood disorders, obesity and cardiovascular disease, jeopardising longevity. More than a third of Americans report that they sleep for less than seven hours on average (known as short sleep duration) but is that enough? What is the optimum number of hours of sleep for health and longevity, and what are the best ways to get them every night?

The need for sleep

Sleep is a recurring state of rest that is controlled by the body’s circadian rhythm, the 24-hour sleep-wake cycle that responds to light and dark. The circadian rhythm times the release of different hormones, including the sleep hormone melatonin and the stress hormone cortisol that increases alertness, effectively controlling the body’s sleep schedule. Getting enough sleep is integral to health and longevity as it maintains several essential functions including tissue repair, muscle growth and protein synthesis, which all occur almost exclusively during sleep. While individual needs vary, it is recommended that adults get a minimum of 7-9 hours of sleep every night. With busy modern life, people can feel pressed to reduce their time spent sleeping in order to maximise their productivity during the day. However, this can have the opposite effect, as even short-term sleep deprivation can be detrimental to mood, alertness and mental focus, hence the phrase ‘got up on the wrong side of the bed’. The short-term consequences of sleep deprivation on the body can be experienced the day after a restless night, and you may feel more irritable and stressed. Lack of sleep can also reduce alertness and the ability to perform tasks. It also impairs memory as we are less able to focus and gather information, therefore making it more difficult to remember things [1].

Effects of sleep deprivation on health and longevity

Long term, getting less than seven hours of sleep per night can accelerate epigenetic aging and increase the risk of developing more serious, chronic conditions that impact longevity. Researchers have even likened the protective health effects of high-quality sleep to that of diet and exercise. Chronic sleep deprivation disrupts the release of hormones that regulate processes like the metabolism, appetite and stress response. Over time, insufficient sleep can increase weight gain and lead to obesity, with those who get less than six hours of sleep per night being more likely to have excess body weight compared to those who get eight hours. It can also develop or exacerbate mood disorders like anxiety or depression, as low mood is linked to lack of sleep and vice versa. It may also reduce the effectiveness of the immune system, leaving the body more exposed to infection and increasing the likelihood of developing a common cold by three times [1].
Cardiovascular diseases like diabetes, heart disease and dementia are chronic conditions related to genetics, nutrition and physical inactivity. Lack of sleep can be considered as another key risk factor in developing such conditions. Studies have shown that fewer than five hours of sleep can increase the risk of developing type 2 diabetes, which is also related to obesity, while longer sleep can have a protective effect and helps modulate blood sugar levels. Furthermore, six to seven hours sleep has been associated with heart disease, the leading cause of death in the United States, by increasing the risk of coronary artery calcification that can lead to heart attacks. Disorders like sleep apnoea can increase the risk of cardiovascular diseases like hypertension, stroke, coronary heart disease and irregular heartbeat [1].
Heart disease is commonly caused by a build-up of plaque in the arteries, known as atherosclerosis, which traps white blood cells from the immune system, narrowing the arteries and limiting the flow of oxygen-carrying blood around the body. One study investigating the molecular mechanisms linking sleep deficiency with heart disease found that mice with interrupted sleep schedules developed larger plaque build-up. They also had lower secretions of the hormone hypocretin, which can supress the production of white blood cells. This suggests that reduced hypocretin levels from lack of sleep could lead to atherosclerosis [2]. While lack of sleep can cause short-term forgetfulness, it has additionally been associated with Alzheimer’s, an age-related disease that severely impairs memory and brain functioning. Alzheimer’s has been linked to build-up of the beta-amyloid protein in the brain fluid, which can accumulate in amyloid plaques and prevent communication between neurons. Sleep may play a vital role in clearing beta-amyloid from the brain, thus reducing the risk of impaired cognitive function and Alzheimer’s. Indeed, sleep deprivation for just one night can increase beta-amyloid in the brain by as much as 5%. Evidently, sleep and Alzheimer’s are closely interconnected, and elevated beta-amyloid may also lead to trouble sleeping, evident in the restlessness experienced by people with Alzheimer’s [3].

Getting a better night’s sleep

The empirical evidence for getting more sleep for longevity is convincing, and we all know from experience the transformative powers of a good night’s sleep. However, consistently oversleeping, defined as sleeping for more than 9 hours, can signify sleep disorders, mental health disorders and other health issues. Oversleeping usually occurs when compensating for sleep deprivation in days prior, and occasionally oversleeping is fine for health. However, chronic oversleeping can have similar long-term health impacts as sleep deprivation including increased inflammation, impaired immune function and cardiovascular disease [4]. 9 hours of sleep appears to be the perfect equilibrium and protects against short- and long-term conditions, and is what we should be aiming for every night. Prioritising sleep, by definition a period of no productivity, in a busy schedule can be difficult. The following tips can be used to help ensure a well-deserved long night’s sleep for longevity:

  • Set a bed time. Usually reserved for children, going to bed at the same time every night trains your body and maintains a regular sleep-wake schedule. It also makes falling asleep easier for those with insomnia.
  • Take a break from caffeine. In the evenings, avoid stimulants like caffeine, alcohol and nicotine as they can interfere with sleep.
  • Transform your bedroom into a comfortable sleep environment using low lighting and comfy pillows. Avoid using your bed for wakeful activities like working, watching TV or using your phone and reserve it for sleep only.
  • Create a calming pre-sleep routine that can involve a relaxing bath, a bedtime book or lighting a candle. Limit your use of electronic devices an hour before bedtime.
  • Sleep in accordance with your body’s circadian rhythm by exposing yourself to light during the day and limiting light exposure in the evening.
  • Try not to nap close to your bedtime to avoid disrupting your sleep schedule.
  • Skip after dinner snacking. While going to bed with a warm mug of hot chocolate is cosy, try to avoid overeating too close to bedtime.
  • Regularly exercising can tire you out physically, making it easier to fall asleep at night. However, try not to exercise too soon before you go to bed.
  • Problem solve any lingering worries during the daytime. During sleep, our everyday worries can make their way from our subconscious in the form of images in dreams and nightmares. Addressing these stressors during the day rather than agonising over them at night can help your subconscious to relax, making it easier to fall asleep.