Early to bed, early to rise: sleep timing and your health

Paula Pienaar explains why sleep timing is important to your health, adding that the time you go to sleep and wake up plays a large role in whether you increase your risk of obesity and Type 2 diabetes.

Traditional lifestyle-related risk factors, such as overeating, poor nutritional choices and physical inactivity, have long been blamed for the alarming global increase in obesity, diabetes and cardiovascular disease. In recent years, it has become evident that sleep habits (sleep timing) also contribute significantly to one’s health risk status. In fact, did you know that the time you go to sleep and wake up plays a large role in whether you increase your risk of obesity and Type 2 diabetes?1-3

Sleep timing is crucial

Studies on how sleep timing affect health have shown that late bedtimes, combined with sleep deprivation (often due to waking up early enough for work) results in increased caloric intake in the late evening hours, as well as increased appetite for foods that are calorie-dense. In addition, later bedtimes seem to have become more frequent in the general population and is associated with an increased prevalence of Type 2 diabetes as well as poorer glucose control in diabetic patients.1,3

The circadian rhythm influences sleeping, eating, heart rate, blood pressure, body temperature, the levels of certain hormones, and the immune system.

Tick-tock our body clock: our circadian rhythms

The time you go to sleep and the time you wake up, or your sleep-wake cycle, is referred to as your circadian rhythm.

This internal body clock is a 24-hour internal timer that functions by cycling between sleepiness and alertness at regular intervals throughout the day.

The pattern of feeling energised and tired at usual times is an example of your circadian rhythm at play.

For most adults, the biggest energy dip occurs between 2:00 am and 4:00 am, when we are meant to be sleeping, and 1:00 pm and 3:00 pm, usually after lunch. These circadian dips are especially prominent in those who are sleep-deprived.

Did you know?

After midday, body temperature drops slightly which prompts the release of melatonin. Although this effect is at a smaller scale compared to nighttime, we often experience it as a ‘post-lunch’ energy dip occurring between 2pm and 4pm.

Social jet-lag

Today’s society has created an illuminated environment that alters the natural light-dark cycle needed to regulate the circadian rhythm. Big cities with 24-hour light exposure, workplaces with bright artificial lighting, and neon lights adorning places of entertainment are all examples of how we are constantly exposed to unnatural lighting during the time when our body needs to wind down.

Additionally, our lifestyle choices may also create a body clock that is out of sync with the environment. For example, our natural rhythm is affected by being awake when we are meant to be sleeping; sleeping for long periods during the day; and even having erratic meal times.

When we intend on ‘catching-up’ on sleep during weekends, or days off from work, we expose ourselves to the same health ramifications, as now we are trying to change our sleep timing once again. This mismatch in sleep time is called ‘social jet-lag’ and affects most of us at some stage in our lives, whether it is due to travel, social engagements or work demands.

Consequences of a disrupted body clock

The sleep disruption and deprivation resulting from irregular sleep times and increased night-time light exposure have shown to disrupt metabolic and hormonal processes.2,4,5

The body responds by:

  • Increasing hunger hormones, which may lead to weight gain and obesity.
  • Suppressing the release of sleep-inducing hormones, making it more difficult to fall asleep.
  • Creates an immune response, which lowers your immune status.
  • Increases stress hormones, which have shown to lead to hypertension and cardiovascular disease.
  • Disrupts insulin action, which favours fat accumulation.

The good news is that by adjusting your sleep routine to follow the environments natural light-dark cycle, you can support your body clock in restoring your health.

Managing sleep timing

The following tips have shown to help improve circadian function and sleep disruption:

  • Ensure adequate exposure to daylight: exposure to sunlight during the day and darkness at night helps to maintain a healthy sleep-wake cycle. This is especially important for people who spend most of their time indoors.
  • Stick to a healthy sleep and wake time routine: try to consistently make your way to bed when it gets dark, and wake up to natural light instead of hitting the snooze button.
  • Ensure the bedroom is dark, quiet and comfortable: cosy temperature; no television, mobile phones and bright lamps (see next tip below); and pets that wake you up should be kept out of the bedroom. The mattress and pillows should also be comfortable. It may be helpful to use blackout curtains, ear plugs, and eye shades.
  • Refrain from screen time at least an hour before going to bed: the blue light from certain televisions, mobile phones and tablet devices suppress the release of sleep-inducing melatonin. It may be useful to use blue-blocking glasses and apps to filter short-wavelength emissions from electronic devices. You can download such an app from https://justgetflux.com/ .
  • Avoid napping during the day, but if the need is very high, limit it to before 03:00 pm and for no longer than 30 minutes. You do not want to end up with a late bedtime and sleep deprivation the following day.
  • Get regular physical activity: moderate activity, such as brisk walking, has shown to help improve sleep quality. If you are a morning-type person, use that to your advantage and get natural morning light during your outdoor sessions.
  • Go camping! A weekend dose of nature’s light-dark cycle has shown to restore a disrupted circadian rhythm.

Shift workers and individuals who travel regularly across time zones are most vulnerable to circadian rhythm disruption and would benefit greatly from sleep-timing support. If having tried these tips, but you still are out of sync, or struggle with excessive daytime sleepiness, it is best to seek help from a sleep health professional.


  1. Knutson, Kristen L., et al. “Association Between Sleep Timing, Obesity, Diabetes: The Hispanic Community Health Study/Study of Latinos (HCHS/SOL) Cohort Study.” Sleep 40.4 (2017).
  2. Baron KG, Reid KJ, Kern AS, Zee PC. Role of sleep timing in caloric intake and BMI. Obesity (Silver Spring). 2011; 19(7): 1374–1381.
  3. Merikanto, Ilona, et al. “Associations of chronotype and sleep with cardiovascular diseases and type 2 diabetes.” Chronobiology international 30.4 (2013): 470-477.
  4. McHill, A. W., and K. P. Wright. “Role of sleep and circadian disruption on energy expenditure and in metabolic predisposition to human obesity and metabolic disease.” Obesity Reviews 18.S1 (2017): 15-24.
  5. Sharma, Arpita, Shashank Tiwari, and Muniyandi Singaravel. “Circadian rhythm disruption: health consequences.” Biological rhythm research 47.2 (2016): 191-213.
  6. Potter, Gregory DM, et al. “Circadian rhythm and sleep disruption: causes, metabolic consequences, and countermeasures.” Endocrine reviews 37.6 (2016): 584-608.

MEET OUR EXPERT - Paula Pienaar

Paula R. Pienaar
Paula R. Pienaar (BSc (Med)(Hons) Exercise Science (Biokinetics)), MSc (Med) Exercise Science) is the scientific advisor to EOH Workplace Health and Wellness, and a PhD candidate at the University of Cape Town. Her scientific research relates to sleep health and managing daytime fatigue to improve workplace productivity and lower the risk of chronic disease. Her thesis will identify the link between sleep and cardiometabolic diseases (Type 2 diabetes and cardiovascular disease) in South African employees. She aims to design a tailored sleep and fatigue management workplace health intervention to improve employee health risk profiles and enhance work productivity. Contact her at [email protected]