Published by NutriScience | 30 min read | Published on April 8, 2021 | Reviewed by Kara Collier, RDN, LDN, CNSC
Blood sugar (or blood glucose) can have a significant impact on your sleep patterns. In fact, uncontrolled glucose levels might be the reason you are having trouble sleeping. Sleep and glucose have a bidirectional relationship. In one direction, how well or poorly you sleep will directly impact your glucose levels. In the other direction, what your glucose levels are like going into the night and during sleep will impact your sleep. Why does it matter? Blood sugar affects sleep, and sleep affects physical health. Short sleep duration—defined by the Centers for Disease Control and Prevention (CDC) as less than seven hours in a 24-hour period—can have a significant impact on your health. Adults who are short sleepers are more likely to have chronic health conditions like diabetes, obesity, or heart disease. So, getting control of your sleep habits can positively affect your health and longevity. We’ll show you how you can do just that by monitoring your glucose levels. Why does sleep affect blood sugar? The relationship between sleep and blood sugar levels is complex. Sleep is essential to allow your body to restore and repair itself. When you don't get enough sleep, several changes occur in your body. Let's explore them one by one.
Sleep impacts insulin levels Sleep affects your hormone levels and your circadian rhythm. Your circadian rhythm naturally controls your sleep-wake cycle by responding to things like light and dark levels. Most people have a reasonably consistent circadian rhythm as adults. There is a small group of nerve cells that form what’s called the “master clock” in your brain. This internal clock controls hormone secretion, temperature, eating habits, and digestion. To work optimally, it requires a consistent circadian rhythm. Keeping this rhythm is key to regulating your metabolism, insulin, and blood glucose, as well as your sleep-wake cycle. When your circadian rhythms are out of sync, your body's metabolic health can decline—and a risk for diabetes can increase. Research published in the journal “Endocrinology and Metabolism Clinics of North America” identifies that sleep deprivation reduces insulin sensitivity. This leads your body to produce more insulin to stabilize blood glucose levels. The more insulin resistant your cells become, the greater the risk that your insulin and blood sugar levels will chronically rise. This eventually leads to glucose intolerance and diabetes. According to the CDC, even just one night of insufficient sleep can affect your body’s ability to use insulin effectively.
Sleep regulates hunger hormones Two hormones that regulate your appetite are leptin and ghrelin. Leptin plays several roles within your body. Two of its key jobs are long-term energy regulation and metabolism. You may have heard it referred to as the starvation or satiety hormone. The fat cells in your body release leptin, telling your brain when you have enough energy. When released, it suppresses your appetite, making you feel satisfied. If leptin levels are low, your appetite increases. Several studies have found that short sleep duration reduces leptin levels, leading to overeating and weight gain. In turn, the craving to eat more results in an increased intake of carbohydrates which raises glucose levels. Ghrelin has the opposite function of leptin, increasing your appetite by telling your brain that your body needs more food. This is one of the reasons why certain fad diets often fail. When you don’t eat enough, ghrelin levels increase, making it harder to stick to your diet. Another thing that increases ghrelin levels is lack of sleep. The surge in ghrelin prompts you to feel hungry, leading you to eat more carbohydrates, which will raise your glucose levels. There is also an added problem with high ghrelin levels, as it can reduce glucose tolerance.
Sleep impacts sympathetic nervous system activity Sleep deprivation, or broken sleep, can lead to an increase in sympathetic nervous system activity. In stressful or dangerous situations, the sympathetic nervous system is what controls your “fight or flight” response. Lack of sleep can cause your “fight or flight” mode to kick in during the day and night, releasing stress hormones like cortisol. When your sympathetic nervous system is overly active, it can reduce insulin secretion and promote insulin resistance. Both of these can lead to chronically raised blood sugar levels. When blood sugar levels become raised, it can cause lifelong chronic conditions such as pre-diabetes, diabetes, or metabolic syndrome.
Sleep modulates inflammation Research shows that sleep deprivation increases inflammation levels in the body. This effect can happen after even a single poor night’s sleep. Inflammation is one of your body’s defense mechanisms, providing valuable protection against viruses and bacteria. But, if inflammation is chronically high, it can lead to lifelong conditions such as metabolic syndrome, type 2 diabetes, heart disease, and obesity. It can also cause further complications and a poorer prognosis. Sleep impacts brain function Glucose is fuel for the brain. It provides the energy needed to carry out its functions. When you’re sleep-deprived, the metabolic activity in your brain decreases significantly. Overall, studies state that sleep deprivation has damaging effects on brain function—particularly functions such as alertness, attention, decision making, and cognitive processes. Sleep helps to regulate body fat Sleep helps to maintain your body weight in many different ways, including regulating hunger hormones and insulin levels, as discussed earlier. Research published in the journal “Diabetologia” shows that lack of sleep increases levels of free fatty acids in your blood. Those high fatty acid levels lead to a reduction in insulin sensitivity and hamper your body’s ability to metabolize fat. Controlling glucocorticoid levels is another body fat regulator. Glucocorticoids are hormones that control several processes such as metabolism, inflammatory response, and brain function. One of the principal glucocorticoids is cortisol (also known as the stress hormone). Studies show that when we’re sleep-deprived, cortisol levels increase both during that night of disrupted sleep and the following day’s long period of wakefulness. When cortisol levels increase, it can lead to insulin resistance. This can lead to an increase in blood sugar, weight gain, and potentially Type 2 Diabetes. So, a lack of sleep negatively impacts your glucose levels in many ways. But what typically happens to your blood sugar levels when you get a good night’s sleep? Do you know what your normal blood sugar levels should be overnight? What happens to blood sugar while you sleep?
Normal glucose levels while sleeping In a healthy individual, glucose levels will go up and down while you sleep, which is normal. Despite this, they should generally stay within the range of 70-100 mg/dl. There is a lot of research available on optimal morning fasting glucose values (after sleeping and fasting for at least eight hours) because these are the values that your physician or a researcher would test at a lab. This research tells us that an optimal waking fasting glucose value is between 70-90 mg/dL. But, there is less research available on what optimal glucose levels are while you’re sleeping. So, the advice is currently to aim for overnight glucose values within the 70-100 mg/dL range most of the night and overnight values that keep your 24-hour average glucose below 105 mg/dL.
To recap, the key glucose levels you are looking to maintain are:
Glucose levels when asleep between 70-100 mg/dL
Optimal morning fasting glucose values between 70-90 mg/dL
Overnight values that keep your 24-hour average glucose below 105 mg/dL
Dawn phenomenon This is a regular occurrence that happens in every person. In the early morning hours, certain hormones (growth hormone, cortisol, and catecholamines) cause the liver to release sugar into the bloodstream. The process may cause a short-term increase in glucose. This is your body’s “natural alarm clock.” For most people, the dawn phenomenon usually occurs between 4 am and 8 am, but it does depend on your sleep-wake cycle. Your glucose levels should come back down within a few hours following the release of insulin.
For those with insulin resistance and/or diabetes, glucose levels have difficulty coming back down after that morning surge. This can lead to higher-than-normal blood sugar levels at the start of the day.
How do blood sugar levels impact sleep? Remember, sleep and glucose have a bidirectional relationship. Not only does a lack of sleep affect your blood sugar levels, but poor glucose levels also negatively affect your sleep. Both too low and too high blood sugar levels can have an impact on your sleep patterns.
High blood sugar There are several reasons why high blood sugar levels affect your sleep:
Pre-bed high blood sugar levels can affect the nervous system, making it hard to fall and stay asleep. This can trigger insomnia and increase cortisol and adrenaline levels, preventing your body from fully relaxing.
You may need to go to the bathroom more often, disrupting your sleep. This is due to your kidneys trying to flush the excess glucose out of your body.
High blood sugar can lead you to feel dehydrated, waking you from your sleep to rehydrate with a glass of water.
They can also cause you to feel hot, irritated, and unsettled, making it difficult to sleep.
Low blood sugar Low blood sugar can occur in both diabetics and non-diabetics. It can also be highly disruptive to sleep. Your blood sugar levels can drop due to stress, alcohol, insulin resistance, and other medical conditions. Symptoms of low blood sugar include dizziness, lightheadedness, and blurred vision. Low blood sugar levels can affect your sleep in the following ways:
It causes the release of cortisol and adrenaline. These hormones wake you up and stir your appetite.
When trying to raise your blood sugar levels back to normal, your body overreacts by increasing your appetite. If you then eat when you should be sleeping, it can upset both your glucose levels and sleep-wake cycle.
Low blood sugar levels can further disrupt sleep by causing insomnia, nightmares, sudden waking, and sweating.
The sleep disruption caused by high/low blood sugar levels can lead to a troublesome loop of both poor sleep and poor glucose control. But, it’s not only sleep duration that impacts glucose levels, making this cycle even more complex. Sleep patterns also play their part in glucose control, so let's explore them a little further, too.
What sleep patterns impact blood sugar levels?
Sleep deprivation occurs when you don’t get enough sleep. The CDC recommends at least seven hours of sleep a night to maintain optimal health. Sleep deprivation is also a form of chronic stress, stimulating cortisol. Inadequate sleep will raise glucose levels. There is no getting around it; if you are not getting adequate and sufficient sleep, then your glucose levels will be higher and increase your risk of insulin resistance. Full stop.
Sleep fragmentation A fragmented night of sleep disturbs your periods of deep sleep. Newer research shows deep sleep (or slow-wave sleep) seems particularly important in regulating hormone balance. That includes both insulin sensitivity and glucose tolerance. A study funded by the National Heart, Lung, and Blood Institute (NHLBI) highlights that African Americans with broken sleep patterns and severe sleep apnea are much more likely to have raised blood sugar levels. Even if you get a total of eight hours of sleep, disruptions and lack of deep sleep can cause glucose levels to be higher. The study produced by the NHLBI advises that better quality sleep leads to better blood sugar control. Sleep insufficiency Sleep deprivation, sleep fragmentation, or a combination of both can cause sleep insufficiency. Once it sets in, it affects our everyday ability to maintain alertness, perform, and remain healthy. It can lead to insulin resistance, as well. One research study showed that participants who slept for just four hours had 40% higher glucose levels on average. The participants’ glucose levels were reaching diabetic status, and on top of that they experienced a 24% decreased insulin sensitivity. REM sleep. REM sleep is a specific stage of sleep which occurs at various intervals throughout the night. During REM sleep, a person often has rapid eye movements, increased body movements, and a faster heart and breathing rate. This is often cited as one of the most important cycles of sleep for recovery and energy. REM sleep has a positive effect on glucose levels, as research shows that levels decrease by an average of 5% during REM sleep. Register for Nikki Warren's September Lecture Series on Better Sleep