Which came first? Obesity, or sleep problems? The associations between the two are undeniable so no matter which you start with, you are likely to experience the other. Let’s take a look at this conundrum…
We Deprive Ourselves of Sleep
Hate to say it, but the top cause of most people’s sleep problems is themselves.
Worldwide prevalence of obesity has more than doubled since 1980. Paralleling the current obesity epidemic is a trend of decrease sleep duration. We live in a 24-hour society with many more opportunities for late night work and leisure activities and very little change to morning obligations such as school and work, leaving a ever shrinking space of available sleep time. The majority of 80+ epidemiological studies done across the globe show that “short sleep” usually defined as less than 6 hours per night increase obesity risk (2). Why, you ask? The primary cause is the disruption of multiple hormone pathways and cycles. In particular, the hormones that are controlling our metabolism and fat storage. When we don’t get proper sleep, we sabotage the interaction of these hormones and our own internal circadian rhythms.
We Have Clocks in Our Bodies
“Circadian clocks” are our internal hormone clocks that keep track of what time it is in a 24-hour period, what activities we are doing, and what we “should” be doing next (to prepare our bodies for it). You may be familiar with the phenomenon of “jet lag”, when your body has to adjust your melatonin production to a new time zone (sunset) that is several hours different than your norm. That adjustment is actually very complicated, as melatonin is mediated by just one of your central (brain-centered) circadian clocks. Not only are there multiple central circadian clocks, peripheral (non-brain) circadian clocks have been found in virtually all tissues! You can imagine the complexity of these clocks all working in synchrony.
Figure - Pathways of peripheral Clock entrainment.
Source: Takahashi et al., 2012 Annu Rev Neuroscience. “Central and Peripheral Circadian Clocks in Mammals”
Late Feeding Disturbs Your Clocks
Feeding is a major synchronizer of the peripheral circadian clocks (think of how your bowels are often stimulated after a meal). Late-night feeding, due to prolonged night time wakefulness, leads to desynchrony between the central and peripheral circadian clocks. Leptin is a hormone secreted by fat cells in response to glucose (sugar; carbohydrates) in the blood and it goes to the brain to convey signals of satiety, which prevents overfeeding. Leptin acts as a time marker to reset central circadian clocks, so eating late is like turning back the hour hand in your brain to say it is only 6:30pm, when it may be almost midnight!
But I don’t eat when I stay up late!
Even if you don’t eat past 6:30pm, studies show that sleep deprivation still causes you to wake up with lower leptin levels, setting you up to overeat that day. One study showed that this decrease averaged 15% for people habitually getting only five hours of sleep. The same study showed that while leptin decreased, the levels of the hormone ghrelin increased. Ghrelin is the hormone that signals appetite stimulation in the brain. So, not only are you not discouraged from eating, but your brain is going to make you feel you must eat more! Another study suggested that if strict caloric intake was maintained for short sleep and normal sleep (8 hours) groups, BMI remained the same in the short term, suggesting that the extra weight gain was purely a factor of increased caloric intake. However, a Japanese study showed that dietary patterns (eating out, high fat, skipping breakfast, late night snacks) only partially explained the weight gain related to sleep deprivation.
Resist Sleep and Insulin Will Resist You
Insulin levels are also affected by sleep deprivation and disrupt circadian rhythms. Two studies done on healthy adults particularly highlight the effect. The first study was on 11 young adults subjected to only four hours of sleep for six nights. Researchers found that their ability to process glucose (sugar) had declined, in some cases to the level of diabetics. (Add in the additional insult of a diet laden with caffeine and sugar and that sounds like many college students to me!) The second study tested healthy men and women with average BMI and found that those who averaged 6.5 hours or less sleep produced 30% more insulin that the normal sleepers (8 hours) in order to keep their blood sugar normal. Basically, you can suffer insulin resistance from sleep deprivation regardless of your carbohydrate intake, family history, etcetera.
We also continuously sabotage ourselves with excessively stressful lives, which often results in uncontrolled anxiety and insomnia. In contrast to the first problem, wherein you may choose to stay up later than you should, with anxiety and stress-related insomnia you end up spending the evening (or middle of the night) staring blankly at the ceiling wishing for nothing more than to be able to sleep! Worse yet is when it is accompanied by the endless rat wheel of worrisome thoughts that drive you mad or into an outright panic attack! Also, usually fitting into this category, is the person who can sleep through the night but wakes just as tired as when they went to bed, often feeling as though they were restless all night. Surprise! Your body may have been sleeping, but it forgot to inform your brain.
Cortisol, King of Hormones
By now, it is probably no surprise to you that these problems are also related to disrupted circadian rhythms. Cortisol (aka “the stress hormone”) is a major modulator for clock re-synchronization. Normally, cortisol is elevated during the day (opposite of melatonin) and gives you the energy and focus you need to perform all day. However, when you have high stress (anxiety is both a cause of stress and the result of it) your cortisol production gets amped up, causing your brain to feel “wired” even when you know your body is tired. Cortisol is released when we drink caffeine, work out, find ourselves in danger, or we are up against a deadline. That release is obviously disruptive when these things occur late at night.
Not stressed? Well, as you may have guessed, that is only part of the equation. Studies have also shown that desynchronization of sleep circadians (sleep deprivation) causes abnormally high cortisol levels during the day. That’s okay, right? Wrong.
Increased cortisol has been associated not only with obesity and sleep disorders, but also with cardiometabolic disease, mood disorders, and tumor growth! Part of the reason for cortisol’s huge impact on your health is its impact on the sympathetic nervous system (stress-response system). This system is counteracted by the parasympathetic nervous system (non-stress operations). Over prolonged periods of stress or elevated cortisol these symptoms get out of balance and the sympathetic system becomes dominant. Thus, it becomes difficult to turn it off quickly, and your cortisol levels will no longer follow normal circadian rhythms. They may remain chronically elevated or low, but both patterns are abnormal. Without the normal diurnal pattern of cortisol levels, you get a perpetual disruption of one of your major circadian regulators.
I hope this article has shed some light the topic of sleep, and how it relates to weight and hormone regulation. Please leave your comments below.
Stay tuned. In a couple of days I will flip the script and look more specifically at how obesity causes sleep problems, thus creating quite a vicious cycle.
With love and commitment to your health in 2019,
Dr Valeska Wells
- Mohawk JA, Green CB, Takahashi JS. Central and Peripheral Circadian Clocks in Mammals. Annu Rev Neurosci. 2012; 35: 445-462
- Gnocchi D, Burscalupi G. Circadian Rhythms and Hormonal Homeostasis: Pathophysiological Implications. Biology. 2017 Mar; 6(1): 10
- Peters B. How Does Being Overweight or Obese Affect Your Risk of Sleep Problems? Verywell Health. 2018
- Winkelman JW, Herzog DB, Fava M. The Prevalence of sleep-related eating disorder in psychiatric and non-psychiatric populations. Psychol Med. 1999 Nov; 29(6): 1461-6.
- Beccuti G, Pannain S. Sleep and obesity. Curr Opin Clin Nutr Metab Care. 2011 July; 14(4): 402-412.
- Obesity and Sleep. National Sleep Foundation