Sleep has a number of health benefits, including memory and learning1. Lack of sleep impairs judgement, impacts longevity and safety, and increases the risk of a number of diseases including obesity, hypertension, heart disease, diabetes, mood disorders and impaired immune function1.
A recent report found that four in 10 Australians frequently suffered from inadequate sleep2. Sleep deprivation was linked to 3,017 deaths – 394 deaths per year from falling asleep while driving OR industrial accidents and 2,623 deaths from heart disease or diabetes2. In fiscal terms, it cost Australia $66.3 billion2.
We wake and sleep because of the actions of two opposing internal forces1. Sleep drive increases throughout the day, but this is opposed by the alerting signal produced by our internal or biological clock2. Only when this signal decreases does the drive to sleep take over. The alerting signal also dips about 2-3 pm, explaining why you may feel more alert in the evening than the early afternoon1. As we sleep, the sleep drive diminishes, but diminishing of the alerting signal is what allows us to sleep 7-8 hours1.
The biological clock controls diverse biological functions, including body temperature and neurohormone secretion3. The daily oscillation of the diverse body functions is termed circadian rhythm, which comes from Latin Circa Diem, meaning ‘about a day’. Various organs have a circadian clock but the primary one is located in the Suprachiasmatic Nucleus (SCN) – a small group of nerve cells in hypothalamus3. The circadian rhythm resets every day to within a few minutes of the Earth’s 24-hour rotation cycle through external cues, the most important being daylight. In the morning the SCN senses light through the optic nerve, raising temperature, heart rate, blood pressure, cortisol levels and delaying the release of hormones like melatonin2. By evening, the SCN again detects changing light, reducing temperature, heart rate, blood pressure, and inducing sleep hormones. The most important hormones relating to sleep are in opposition – cortisol the alerting hormone is secreted in the morning and melatonin, the drowsiness hormone, is secreted at night.
White (visible) light is made of the colours of the rainbow. Blue light has more thermal energy; red light has the least power to shift circadian rhythm and suppress melatonin4. Nature reflects this with the blue sky of day and red/orange/yellow of sunsets and fires – once our only source of light, and heat. Our daily schedules don’t follow sunrise and sunset anymore. Our fast-paced schedules of working, studying and late nights is constantly fighting our master clock. Blue light from the sun wakes us up in the morning, increasing alertness and improving mood and performance. The cells of the SCN are most sensitive to blue light. Blue light at night from light globes and modern technology e.g. TVs, computers, smart phones can interfere with a person’s circadian rhythm and melatonin secretion.
The US National Sleep Foundation recommends adults aged 26-64 years obtain on average 7-9 hours’, range 6-10 hours’ sleep per night5. To determine your personal sleep needs, chose a window of a few days where stress and demands on you are low. On the first night, retire at your habitual bed time and let yourself wake naturally and refreshed the next morning (ensure sunlight doesn’t make you up). Repeat this until you have consistent sleep hours – should be that required by your body to function optimally6. Almost 20 years ago, sleep research pioneer, William Dement MD said “we are not healthy, unless our sleep is healthy”6.
Strategies to help you get your best night’s sleep:
Be exposed to 10,000 lux for 30 minutes every day7. The best time to do this is when the circadian rhythm is the most responsive – 6.00 to 8.30am. In winter, exposure of natural light through eyes, even on cloudy day will produce favourable response (1000-2000 lux compared to 50-500 lux from indoor lighting; brightest sunlight emits 120,000 lux). If you work indoors, try to take breaks outside throughout the day. Light boxes, used to treat Seasonal Affective Disorder during darker winter months can help, but chose one that is rated at 10,000 lux.
Turn off the screens, including TV, radio and mobiles to help your mind and body switch off well before bed time to allow melatonin and cortisol levels to normalise. Replace screen time with reading a book, listening to music, talking to spouse and/or children face to face – about how their day went, what they are excited about or struggling with. Use blue light blockers on devices to help make more melatonin at night. F.Lux is available for computers and appears to effectively reduce blue light. In a recent study, the iPad’s Night Shift mode was found to be insufficient for preventing impacts on melatonin suppression8 – iPhones were not tested. If you are a shift worker or if have to use electronic devices at night, blue blocker glasses are beneficial.
Caffeine and alcohol
These affect adenosine, a neurotransmitter which decreases neural activity and facilitates sleep. Caffeine blocks adenosine receptors so you have less deep sleep and more night time awakening1. Caffeine as a half-life of 4-7 hours, so avoid after 2 p.m., or noon if especially caffeine-sensitive9. Alcohol alters the signaling of adenosine so you fall asleep quickly, but like caffeine, also affects deep sleep1. Alcohol consumption carries health risks, therefore the recommendation is to avoid alcohol10-12. But if you still chose to drink, avoid it within 3 hours of bedtime.
Regular sleep schedule keeps the circadian sleep/wake cycle synchronised – fewer reports of insomnia and depression1. So, get up the same time everyday even after a late night or fitful sleep. Aim to go to sleep within a few hours of it getting dark. Be guided by season, somewhere between 9.00 and 11.00pm.
These activate the vagus nerve, affecting the circadian clock and visa versa13. They also activate gut endocrine system and are primary producers of neurotransmitters and neuropeptides e.g. dopamine, serotonin and GABA. In fact, the gut has 400 x more melatonin than pineal gland in brain14. So, eat a wide range of whole, minimally processed plant foods of varying colours – vegetables, fruits, and whole grains – which are high in fibre and nutrients, as these are instrumental in restoring and protecting the beneficial bacteria in your gut, and avoid eating 3 hours before bedtime.
This enables falling asleep faster with more time in deep sleep and less night time awakening1. It increases serotonin synthesis/release and also increases tryptophan15. Working out in the morning or afternoon is fine but the early morning seems to be the most beneficial time as it facilitates greater time spent in deep sleep16. Exercise (aerobic, resistance, stretching) stimulates the body to secrete the stress hormone cortisol, which helps activate the alerting mechanism in the brain, so, avoid within 2 hours of bedtime and choose quieter activities after dinner to prepare your body to wind down.
Taking to bed worries about a problem or a long to-do list can be a recipe for insomnia. Stress, aka fight or flight response, is a normal sympathetic response to danger, but has become chronic in our fast passed world. Even perceived threats can activate this response. But we can switch to the parasympathetic response, known as rest and digest response. During stress, our breath is shallow and rapid – sympathetic, but it can be switched to a relaxation – parasympathetic – response through rhythmic deep breathing. Mindfulness and meditation can also help. Mindfulness is not rushing off into future thinking about all the things you need to do. Meditation is the act of giving your attention to only one thing, either as a religious activity or as a way of becoming calm and relaxed17.
Well before you turn in, write down worries and list of tasks you want to remember in a “worry journal”. Closer to bedtime, try comforting rituals that may help lull you to sleep, such as soft, calming music; a warm bath; reading by soft light; sitting quietly and focusing on your breathing. Once in bed or if wake up in night and can’t get back to sleep within 20 minutes, get out of bed and do something relaxing until you feel sleepy again, but keep the lights dim.
Blocking out light18 is one key, as is temperature19,20. Core temperature drops to help initiate sleep and insomniacs appear to have higher core temperatures20. We seem to sleep best at room temperature around 16 – 24oC (most commonly 18oC). Mattress cooling pads may help in those with higher core temperatures21. A quiet bedroom is also important, particularly for older adults who spend less time in deep sleep22. Run your appliances before bedtime. White noise, e.g. fan, air purifier, nature recordings can calm and elicit sleep.
Dr Lillian Kent is a senior researcher in the Lifestyle Research Centre at Avondale College of Higher Education, a Fellow of the Australasian Society of Lifestyle Medicine, and a Registered Public Health Nutritionist with the Australian Society of Nutrition.
- Sleep Medicine Division. Healthy Sleep. Harvard Medical School. Boston; 2018 http://healthysleep.med.harvard.edu/healthy/
- Sleep Health Foundation. Asleep on the job – Costs of inadequate sleep in Australia. Sleep Health Foundation. Sydney; 2017 https://www.sleephealthfoundation.org.au/files/Asleep_on_the_job/Asleep_on_the_Job_SHF_report-WEB_small.pdf
- Gillette MU, Tischkau SA. Suprachiasmatic nucleus: the brain’s circadian clock. Recent Progress in Hormone Research. 1999; 54: 33-58.
- Physical Central. Which color is hotter, red or violet? American Physical Society. 2018. http://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20080411025139
- National Sleep Foundation. Sleep duration recommendations. National sleep Foundation. Washington; 2015. https://sleepfoundation.org/press-release/national-sleep-foundation-recommends-new-sleep-times
- Dement W. The Promise of Sleep. Random House USA Inc. 2000. ISBN: 9780440509011
- Stothard ER et al. Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend. Current Biology 2017; 27: 508–513.
- Nagare R, Plitnick B, Figueiro MG. Does the iPad Night Shift mode reduce melatonin suppression? Lighting Research & Technology. 2018; https://doi.org/10.1177/1477153517748189
- Institute of Medicine. Caffeine for the Sustainment of Mental Task Performance. Chapter 2 Pharmacology of Caffeine. Institute of Medicine (US) Committee on Military Nutrition Research. Washington (DC); 2001.
- GBD 2016 Alcohol Collaborators. Alcohol use and burden for 195 countries and territories, 1990–2016: a systematic analysis for the Global Burden of Disease Study 2016. Lancet 2018; https://www.thelancet.com/journals/lancet/article/PIIS0140-67361831310-2/fulltext
- Topiwala A et al. Moderate alcohol consumption as risk factor for adverse brain outcomes and cognitive decline: longitudinal cohort study. British Medical Journal 2017; 357: j2353.
- World Cancer Research Fund, Nutrition, Physical Activity and Cancer: a Global Perspective. Third expert Report. Continuous Update Project Expert Report. World Cancer Research Fund/American Institute for Cancer Research. Diet; London; 2018.
- Mu C, Yang Y, Zhu W. Gut Microbiota: The Brain Peacekeeper. Frontiers in Microbiology. 2016; 7: 345.
- Benedict C et al. Gut microbiota and glucometabolic alterations in response to recurrent partial sleep deprivation in normal-weight young individuals. Molecular Metabolism 2016; 5: 1175-1186
- Young SN. How to increase serotonin in the human brain without drugs. Journal of Psychiatry Neuroscience. 2007; 32: 394–399
- Fairbrother K et al. Effects of exercise timing on sleep architecture and nocturnal blood pressure in prehypertensives. Vascular Health and Risk Management. 2014; 10: 691–698.
- Singer T. What type of meditation is best for you? Greater Good Magazine. University of California Berkley; 2017 https://greatergood.berkeley.edu/article/item/what_type_of_meditation_is_best_for_you?utm_source=Greater+Good+Science+Center&utm_campaign=20f837472e-EMAIL_CAMPAIGN_GG_Newsletter_Julyl_3+2018&utm_medium=email&utm_term=0_5ae73e326e-20f837472e-51505647
- Gooley JJ et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. Journal of Clinical Endocrinology and Metabolism. 2011; 96(3) :E463-72.
- Del Bene VE. Chapter 218 Temperature. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Walker HK, Hall WD, Hurst JW, editors. Boston: Butterworths; 1990.
- Gradisar M et al. Do chronic primary insomniacs have impaired heat loss when attempting sleep? American Journal of Physiology: Regulatory Integrative and Comparative Physiology. 2006; 290: R1115–R1121
- Sleep solutions website to purchase cooling aids https://www.sleepsolutions.com.au/temperature-control
- Basner M, Müller U, Elmenhorst E. Single and Combined Effects of Air, Road, and Rail Traffic Noise on Sleep and Recuperation. Sleep. 2011; 34(1): 11–23.