Everyone knows that eating a nutritious diet and exercising regularly is important for health and disease prevention, but most people don’t know that a good night of sleep is especially important in maintaining your metabolic health.
This is particularly important now: when you look at all Americans, only 12% meet the criteria for being metabolically healthy! What does it mean to be metabolically healthy? It means your body is equipped to utilize and store energy properly and can be gleaned by looking at things like weight, blood pressure, cholesterol, insulin, and blood sugar levels.
We want our metabolic metrics on point because our daily lives can greatly suffer when these are off base. Insulin and blood sugar levels not optimal? These two factors alone could mean you’re set up for weight gain, infertility, balding and hair loss, dementia and memory impairment, erectile dysfunction, acne, depression, anxiety, chronic pain, and increased appetite.
When you’re dealing with something as fundamental as metabolism, dysfunction can lead to a wide variety of symptoms in the short and long term. This is why it’s so important to understand the integral role of sleep in maintaining metabolic health.
What’s more, getting consistent, quality, uninterrupted sleep is a key factor in preventing chronic diseases like obesity, type 2 diabetes, heart disease, stroke, and Alzheimer’s, all diseases that are also related to metabolic dysfunction. These conditions are sharply on the rise, together affecting hundreds of millions of Americans, and perhaps not coincidentally, sleep duration has inversely decreased from an average of 9 hours per night a century ago to just 6.8 hours per night today.
Increasing rates of obesity over time. Source: NIH
Increasing rates of diabetes over time. Source: CBC
But what if we just lose a bit of sleep every once in a while? The truth is, even intermittent sleep deprivation can cause metabolic health problems. In one study, 11 healthy young men were subjected to 6 nights of sleep deprivation with just 4 hours of sleep, followed by 7 nights of 12 hours of sleep. On the 5th day of each of these scenarios, they underwent a diagnostic test called an oral glucose tolerance test -- a test commonly used to diagnose diabetes -- to see how their metabolism handled a controlled amount of oral sugar.
During the sleep deprivation condition, the subjects did terribly on the glucose tolerance test: they exhibited signs of insulin resistance and impaired metabolism. The rate at which they were able to clear the sugar out of the bloodstream was 40% slower than when they were well-rested!
Insulin is the hormone that is released when glucose enters the body, and it tells cells to absorb glucose; when glucose levels and insulin levels are chronically high, it can lead to “insulin resistance,” whereby the cells become “numb” to all this insulin signaling and end up needing more insulin to get the sugar in the cells. Alarmingly, this short, 6 night period of sleep deprivation generated metabolic profiles in healthy young men that were similar to people with type 2 diabetes. In short, we don’t want to miss out on adequate sleep, even if it’s just for a few days in a row.
In another study of healthy, normal-weight individuals, those who frequently slept short amounts (less than 6.5 hours per night) performed similarly on an oral glucose tolerance test to normal sleepers (7.5-8.5 hours of sleep per night), but the short sleepers had to secrete 50% more insulin than the normal sleepers to achieve these similar glucose results. This is not good, because high levels of insulin over time can lead to insulin resistance, and also act as a brake on the body’s ability to burn fat for energy, thereby contributing to weight gain. We want insulin levels to be fairly low and stable, and sleep deprivation appears to sharply counteract this.
So if less sleep is bad, is more sleep always better for metabolic health? Not necessarily. It appears the magic number for metabolically-optimized sleep is between 7 to 8 hours per night. Below this, and risk of diabetes increases sharply for each hour lost. Above 8 hours of sleep per night, the risk also increases. We want to hit that sweet spot.
The risk of type 2 diabetes increases with too much or too little sleep. Source: ADA
Aside from sleep duration, sleep quality seems to have a big impact on metabolic health. A study of adult men followed for 8 years showed that those subjects who reported interrupted sleep and difficulty maintaining sleep had 2-3 times the risk of developing type 2 diabetes.
Why does sleep deprivation lead to problems with glucose, insulin, and metabolic health? It may be because the regulation of glucose and insulin are in part controlled by cortisol (our “stress hormone”), which is naturally lower during the evening and early part of the night. Since cortisol is usually low at night, our glucose levels tend to stay lower and more stable overnight. However, sleep deprivation for just 6 days can cause an increase in cortisol levels, which can cause blood sugar to be elevated.
Cortisol signals to the body that something “stressful” is happening, and tells the body it needs to get prepared to have energy against this perceived or real threat. To help the body get ready, cortisol mobilizes stored glucose from the liver into the bloodstream. Cortisol also decreases insulin production from the pancreas and reduces insulin sensitivity in the body, meaning that glucose is less likely to be taken up by cells, and remains in circulation.
Aside from cortisol, sleep restriction may cause an increase in growth hormone, which may decrease glucose uptake by the muscles, causing blood glucose to rise.
Sleep deprivation may make you hungrier, too, leading to an increased likelihood of overeating. A study of 12 healthy young men who had sleep-restricted for 2 days had an elevation in the hunger hormone ghrelin, a decrease in the satiety hormone leptin, and reported increased hunger and appetite, especially for calorie-dense, high carbohydrate foods.
Inflammation in the body is also closely linked with sleep deprivation, with experiments showing an increase in pro-inflammatory chemicals like IL-6, TNF-a, and CRP, which all happen to be immune markers that are also increased in obesity and type 2 diabetes. There appear to be many shared underlying mechanisms linking sleep loss and metabolic diseases.
No matter how healthy our diet and exercise routines are, optimal sleep quantity and quality are critical for maintaining metabolic health. Especially in light of our metabolic disease epidemic, and with rampant levels of largely preventable obesity, high blood pressure, diabetes, and heart disease, we can feel empowered in knowing that tweaking our sleep schedule and sleep conditions could have a huge impact on our health, productivity, and performance. So how do we get our sleep on track?
For starters, making sure the bedroom is dark and quiet, the temperature is right, pets and other distractions are out of the room, screens are off, and you have a high-quality mattress are good first steps in sleep hygiene. The harder -- but equally important part -- is arranging your schedule so that you can carve out an adequate amount of time for sleep: the goal should be 7-8 hours. The research suggests that it’s worth our every effort, and the metabolic payoff is huge.
As mentioned earlier, aside from preventing chronic diseases, having stable and healthy glucose and insulin levels can positively impact all sorts of aspects of our current wellness, including our levels of energy, inflammation, memory, mood, immune function, fertility and sexual health, skin health, and more.
How do we know that our efforts with sleep hygiene are positively impacting our metabolic health? We can measure our waist circumference with a tape measure and make sure it meets healthy criteria, take our blood pressure at home, get our cholesterol checked, and track our glucose with a finger stick or -- better yet-- with a continuous glucose monitor that painlessly samples glucose 24 hours a day and lets you know exactly how sleep, diet, exercise, and stress are affecting your glucose levels in real-time.
Hopefully, after reading this article you feel you have some additional knowledge and tools to prioritize sleep in order to improve your metabolic health. The beauty is that a lot of it is in our control!