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.