However, when it comes to either concern, there's a well-established association between insufficient sleep and obesity.
While there are a multitude of factors that determine whether these two are linked for any particular individual, the odds still suggest that losing sleep is one of the main reasons why we are overweight.
What we're talking about when we talk about sleep loss
Sleep loss generally refers to not getting enough sleep. This could be for any reason; life is full of reasons for missing sleep, and they're not always bad ones. However, the loss of sleep becomes an issue when it happens more than every once in a while. Make it a habit, and you'll experience, first hand, its adverse side effects.
Other terms to consider:
Insufficient or inadequate sleep describes the incidence of not getting the recommended amount of sleep necessary in order to have normal mental and physical function and performance. What are the recommended amounts of sleep we need?
Occasionally, people will have insufficient sleep because they have an early plane to catch (for instance) or their sleep was interrupted by normal means (such as a sick child in need of care or a nocturnal pet looking for attention).
Restricted sleep is the voluntary act of sleeping less than is recommended (usually because of a social or work-related situation). Generally, most people restrict their sleep from time to time, but normally recover. Also, sometimes sleep restriction is used to reset one's circadian rhythms, such as in the case of recovering from jet lag across several time zones.
Sleep deprivation describes the altered state of your body's and brain's functionality after losing sleep over a period of time. To be sleep deprived means you are not getting sufficient or adequate sleep on a regular basis.
The result: changes in hormone levels, daytime symptoms, reduced physical and mental performance, mood dysregulation, and the potential for developing other chronic health conditions like hypertension, obesity, or diabetes, and the likelihood for traffic accidents, mistakes made at work, and relationship problems increases.
Chronic sleep deprivation culminates in what is known as a sleep debt. For many, sleep debt can be difficult to reverse if the continued and chronic loss of sleep has been going on for months or years.
Sleep debt most certainly guarantees that sleep loss will lead to developing major life-threatening conditions like stroke, depression, heart disease, metabolic syndromes, and other diseases and disorders, as well as amplified risk for accidents, injuries, and mistakes in judgment that can have dangerous consequences.
What we're talking about when we talk about weight gain
The Centers for Disease Control and Prevention (CDC) correlates many, if not most, of our most chronic adverse health outcomes with direct measures of body fat.
In light of this, here are some terms to consider.
Body Mass Index (BMI) describes the screening tool used to identify people who are overweight or obese.
Being overweight refers to having a BMI score of between 25 and 30.
Obesity refers to having a BMI score higher than 30.
These definitions are widely used and provided by the CDC, which further categorizes obesity as:
- Class 1: When BMI measures between 30 and 35
- Class 2: When BMI measures between 35 and 40
- Class 3: When BMI measures higher than 40 (also known as “extreme,” “morbid,” or “severe” obesity)
Explaining why we gain weight may seem like a fairly simple exercise in cause and effect. You gain weight usually because you consume more calories than you burn.
But is it really that simple? Weight management depends upon other factors, such as rate of metabolism, activity levels, and hormone balances, all of which can be influenced by sleep loss.
Let's talk about lost sleep and gained weight
The rise in obesity across the world has been paralleled by a trend in sleep loss among both adults and children. The majority of research into links between obesity and sleep suggests chronic partial sleep loss increases the risk for becoming obese.
This visual map from HealthGrove/Fusion (right) charts both trends and mirrors these findings.
Among the most prominent studies is one known as the Wisconsin Nurses’ Health Cohort Study, which followed more than 60,000 women for more than 15 years; obesity rates among these volunteers were positively correlated with sleep loss (in this case, among subjects who slept 5 hours or less nightly). Women with higher sleep debt were 30 percent more likely to gain 30 pounds over the period of the study than those subjects who slept at least 7 hours nightly.
For children, more recent studies suggest a similar trend. According to data published in Pediatrics in 2014, chronic sleep loss between birth and school age results in higher risks for obesity by mid-childhood. Researchers in that study agree: Improving childhood sleep "could be an achievable intervention" for reducing the incidence of childhood obesity.
What happens if these children do not overcome weight gain? They become obese adults and experience a lifetime of related problems.
Why should we worry about sleep if it's BMI we're most concerned about?
Sleeping is not the only circadian process that our brains and bodies experience. Sleeping and wakefulness are primarily regulated by our central circadian system, but we have "body clocks" in every system and cell in our bodies.
Eating holds a significant amount of influence over those circadian rhythms regulated "peripherally" by the digestive system. Problems with overeating, or eating "off schedule," or metabolism profoundly impact our ability maintain a healthy weight.
Sleep loss and slowed metabolism
Research has shown a relationship between sleep loss and changes in cortisol levels, which can lead to slower metabolic rate (the body doesn't burn fuel as efficiently as it might); insulin resistance may also occur. Also, thyroid stimulating hormone (TSH) levels are reduced as a result of sleep deprivation. In both situations, weight gain can result.
Sleep loss and higher incidence of overeating
Clinical studies demonstrate a link between sleep loss and reductions in the hormone leptin. This substance regulates satiation (our sense of feeling full). Without appropriate levels of leptin in the bloodstream, overeating can become a problem which can logically lead to eventual weight gain.
Sleep loss and increase in hunger drive
The hormone ghrelin regulates our hunger drive. After regular sleep loss occurs, higher amounts of ghrelin in the bloodstream amplifies our desire to eat more, and we can begin to crave unhealthy foods that are higher in fat, as well. This becomes yet another reliable predictor of obesity.
A study by King's College in London published just last month indicates that sleep-deprived people tend to consume 385 calories more a day than their well-slept counterparts due to dysregulation of both leptin and ghrelin as the result of sleep loss.
Sleep loss makes active living harder to achieve
Daytime fatigue and reduced physical and mental performance are two outcomes of sleep loss which can make it more difficult to exercise, or to even choose to exercise, especially if the other alternative is to take a nap. Prolonged periods of sedentary living becoming a self-fulfilling prophecy, then: less activity means fewer calories are burned, and that leads to weight gain.
Some sleep disorders are more prevalent among the obese, further increasing the odds for sleep loss
Untreated sleep disorders are frequently associated with disturbed sleep and a higher incidence of weight gain.
Around 18 million Americans suffer from sleep apnea, which is often associated with people who are overweight. While not all people who suffer from sleep apnea are obese, many people who are obese find themselves more likely to develop sleep apnea.
Sleep specialists Margaret Moline, PhD, and Lauren Broch, PhD, of New York Weill Cornell Medical Center, explain that "As the person gains weight, especially in the trunk and neck area, the risk of sleep-disordered breathing increases due to compromised respiratory function."
People who are obese have been shown to be more significantly likely to report insomnia or difficulty with sleep, according to a Nature of Science and Sleep report in 2013. These subjects were more likely to develop chronic insomnia, to lose more sleep due to complaints of chronic emotional stress, and to be more predisposed to overeating.
Also, eating as an emotional behavior may come into play here, with some insomniacs using food as a comfort object, especially during the night when they are awake but should be asleep. These midnight snacking behaviors can also contribute to weight gain.
The conclusion of a study focused on obesity, sleep deprivation, and diabetes, published in Sleep Medicine in 2008, makes it clear:
"Adequate sleep duration and quality are important for the normal functioning of daily metabolic and hormonal processes and appetite regulation. It is clear that chronic sleep deprivation has deleterious effects on carbohydrate metabolism and is associated with an increased risk of diabetes....
"With the marked changes in sleep patterns that seem to have occurred in westernized countries over the last 50 years and an apparent reduction in average hours of sleep way beyond that predicted by aging of the population alone, it is probable that an increasing proportion of people suffer from chronic sleep deprivation.
"This has important implications for individual physical and psychological well being and serious consequences for society as a whole. Avoiding the build up of a chronic sleep debt through awareness, education and effective management of sleep disorders may be important to limit the rise in cardiometabolic dysfunction, diabetes and obesity that has occurred over recent years."
American Journal of Epidemiology
Centers for Disease Control and Prevention (CDC)
Current Opinion in Clinical Nutrition & Metabolic Care
Harvard School of Public Health
National Sleep Foundation
Nature of Science and Sleep