It is a well-documented fact that cardiometabolic diseases and obesity are leading causes of death across the world. In fact, according to the World Health Organisation, at least 2.8 million people die each year as a result of being obese or overweight. Once associated with high-income countries, it is now present in low and middle-income countries too.
Research conducted on the dietary effects of unhealthy food habits on obesity, in particular caused by eating too much and moving too little, suggests that high amounts of energy, (especially fat and sugar) that has not been burned off through exercise and physical activity, remains stored as fat in the body. However, the quality of sleep you get every night is an also crucial factor contributing to cardiometabolic diseases and obesity.
So what really is sleep and what are its benefits?
According to the National Institute of Neurological Disorders and Stroke (NINDS), it is important that we spend close to 1/3rd of our time sleeping. It is as essential as eating or drinking water. Without adequate sleep, our brains are unable to form and nourish neural pathways. Benefits of sleep include a sharper mind, mood regulation, a healthier heart, blood sugar control, weight management and overall better immunity, among others.
What is the Architecture of Sleep?
The architecture of sleep is characterised by Deep Sleep (Non-Rapid Eye Movement or NREM) and REM Sleep (Rapid Eye Movement). During different stages of sleep, different metabolic processes of the body occur for growth, repair, restoration and maintenance.
When you fall asleep, you enter light stages of Deep Sleep (Stage I and Stage II) where the brain and heart slow down. After 20 mins of falling asleep, one tends to fall into the stages of Deep Sleep (Stage III and Stage IV). After about 70 minutes, we go into REM Sleep. Each cycle of sleep (Deep + REM) lasts about 90 minutes. The first half of the night is predominantly NREM, and the second half is predominantly REM sleep.
Various sleep stages can affect your metabolic health in different ways, highlighted in this article talking about Connection between Sleep stages and metabolic health.
How is sleep related to our metabolic health?
According to a study examining the relationship of sleep quality and time with energy metabolism, poor quality and decreased quantity of sleep is a proven risk factor in developing obesity and cardiometabolic diseases. A disruption in the sleep cycle unsettles the circadian rhythm, which serves as our body clock, which in turn leads to an increase in the levels of adiposity.
Our sleep-wake cycle is regulated by something known as the circadian rhythm, a natural, internal process that repeats approximately every 24 hours. It is, in essence, our biological clock. It allows organisms to anticipate changes in the light-dark environment, between day and night and also regulates and influences sleep, arousal, feeding and metabolism. The circadian rhythm is tethered to the rotation of the earth. Today, we’re able to understand better than ever how it affects our metabolic health. Melatonin is a type of hormone known for controlling our sleep cycle in the circadian rhythm. It’s a signal to our bodies that it is time to go to bed.
A molecular clock that modulates the timing of every physiological process like the secretion of hormones and neurotransmitters, the immune cell activity and the time you feel sleepy, alert or depressed, keeps ticking within every cell of the body. These timekeepers work in harmony with each other and with the time of the day. This synchronicity is achieved through the suprachiasmatic nucleus (SCN), a small speckle of brain tissue. It functions in tandem with photoreceptive retinal ganglion cells (ipRGs), light-receptive cells behind the eye. The purpose of these clocks is to foresee and prepare for consistent events in the environment. Varied biochemical reactions are at work at different times of day, facilitating our internal organs to switch gears and recover.
“Unless we have access to light, we struggle to stay awake and eat at the wrong time,” asserts Satchin Panda, a circadian biologist.
Poor sleep may also decrease BMR. A low Basal Metabolic Rate (BMR) (the amount of calories your body uses to maintain vital functions, such as breathing, heart rate, and brain function in the absence of any physical activity), impaired thermogenesis (the production of heat in the body as a byproduct of metabolic processes) and low physical activity levels could result in less energy burned.
Metabolic syndrome refers to a cluster of conditions that simultaneously occur and increase your risk of heart disease, stroke and type 2 diabetes. These conditions include high blood pressure and blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels. According to a study examining the association between sleep duration and metabolic syndrome, less than 6 hours of sleep is correlated with elevated waist circumference among both men and women and with metabolic syndrome among men. Over 10 hours of sleep is associated with metabolic syndrome and elevated triglycerides among men and women and with elevated waist circumference, reduced HDL-C, and raised fasting glucose among women. Metabolic health is tied to both inadequate and excessive sleep.
Variations in your sleep schedule can also affect metabolic health. A study about sleep regularity and metabolic abnormalities found that every 1 hour of day-to-day alteration in bedtime or length of sleep raised the risk of developing metabolic risk factors by 27%.
There is mounting data that loss of sleep and related disorders have a huge impact on metabolism. Deprived sleep can alter the way glucose gets metabolised in the body and disrupt the hormones that control metabolism. Leptin, a hormone that regulates appetite and fat storage, and ghrelin, the hunger hormone which signals the brain to eat are affected. While gender is not directly associated with poor sleep and its effects on metabolism, some studies (Ayas et al. and Mallon et al) have shown that sleep duration can predict diabetes in women. There is a proven intersectional relationship between sleep, physical activity and sedentary behaviour. A study found that the shorter the duration of sleep, the higher the time you spend being sedentary.
A study found that even intermittent sleep deprivation can cause metabolic health problems. This brief 6 night phase of partial sleep deprivation yielded metabolic profiles in healthy young men that were similar to people with type 2 diabetes.
The relationship between sleep and sedentary behaviour need to be studied further, as the research is at a preliminary stage. Even though a sedentary lifestyle and sleeping are both low energy expenditure behaviours, their effects on metabolism and weight gain can be the opposites of each other. Sedentary behaviour becomes a valid risk factor for obesity when done for longer durations, while sleep can be protective against weight gain when carried out in healthy amounts.
Building Good Sleep Habits
According to the Centers for Disease Control and Prevention, good sleep habits, sometimes also known as sleep hygiene, can help you get sufficient sleep, both in terms of quantity and quality. Some habits that can improve your sleep health:
- Consistency: Going to bed at the same time each night and getting up at the same time each morning, including on the weekends
- Bedroom environment: Keeping your bedroom quiet, dark, relaxing, and at a comfortable temperature
- Electronic devices: Removing any electronic devices, such as TVs, computers, and smartphones, from the bedroom
- Food: Avoiding large meals, coffee or caffeinated beverages, and alcohol before bedtime
- Exercise: Getting some exercise. Being physically active during the day can help you fall asleep more easily at night.
National Sleep Foundation guidelines strongly advise that healthy adults get between 7 and 9 hours of sleep per night, while babies, young children, and teens should sleep even more, as it enables their growth and development.
Poor sleep and sedentary behaviours over prolonged periods can potentially be a double whammy for an imbalance in energy metabolism, weight gain, cardiometabolic health and obesity. A consistent sleep schedule is recommended for optimal metabolic health and may even help stabilise other markers.