Two common health conditions experienced by many people are insulin resistance and sleep disturbances, and it turns out the two are related. Insulin resistance is the basis for Type 2 diabetes. According to the American Diabetes Association, at least 10.5% of the population had diabetes in 2018.1
Yet, testing of more than 14,000 people using an oral glucose tolerance test by Dr. Joseph Kraft has shown people can have abnormally high insulin levels with a normal glucose response using a glucose tolerance test.2
He calls this condition diabetes in situ3 and believes by correcting high insulin levels, which lead to insulin resistance, you can also directly and indirectly prevent damage to your vascular system.
Kraft’s testing demonstrated that the prevalence of insulin resistance is far higher than originally thought and greater than the estimates of people with diabetes.4 By the same token, the number of people who have difficulty getting adequate amounts of quality sleep each night is also higher than you may expect.
For several years, The Mattress Firm has commissioned a survey to look at sleep habits and the number of hours people are sleeping each night. The results from 2019 show that Americans are sleeping fewer hours and they are less satisfied with the quality of their sleep.5
On average, 52% of those answering the survey reported getting six hours or less per night of sleep and 40% rated the quality of sleep as “not very good” or “not good at all.” This may be related to the activities they routinely do where they sleep, including watching television, eating and playing video games.
Sleep disturbances or disorders affect nearly 70 million people in the U.S. They include sleep apnea, insomnia, narcolepsy and restless leg syndrome.6 Yet, medical conditions are not the only reason your sleep may be disturbed. Experts also find long naps after lunch, eating within a few hours of bedtime and consuming too much caffeine can all affect sleep quality and quantity.7
Blood Glucose and Insulin Raise Core Body Temperature
The body is in a constant state of thermoregulation, which it achieves through complex interactions between the hypothalamus, muscles, nervous system and vascular system. This process tightly controls body temperature in the face of ambient temperature in your surroundings and your internal heat generation.
Your body requires this for homeostasis and to preserve a stable internal environment in which enzymes, proteins and hormones continue to work.8 Even a shift of a few degrees in body temperature can have disastrous results on your health or your life.9 The balance to maintain core body temperature is a form of homeostasis, which is affected by glucose control and insulin levels.
As Kraft demonstrated, hyperinsulinemia often predates insulin resistance and symptoms of diabetes. A team of researchers from The Scripps Research Institute has found that high levels of insulin raise core body temperature in an animal model.10
This may mean that even people without insulin resistance can experience a rise in core temperature after consuming a meal high in carbohydrates that drives insulin secretion. Blood glucose levels can also reduce your ability to dissipate heat and thus maintain body temperature.
Your body uses sweating as one way of getting rid of excess heat produced during metabolism, from activity or other external stimuli. Thermoregulatory sweating is predominantly controlled by the hypothalamus.11 As core body temperature rises, it can have negative consequences on your cardiovascular system and glycemic control.
Researchers have found people who have poor blood sugar control with diabetes-related complications are particularly vulnerable to poor temperature control.12 However, any person, with or without diabetes, can experience elevation in core body temperature with rising blood sugar levels that may happen after a meal high in carbohydrates.13
Elevated Glucose Makes Exercise and Sleep Challenging
To remove excess heat created during metabolism or exercise, your blood vessels normally fluctuate in size to accommodate thermoregulation. The blood vessels around your organs and in your core constrict, sending more blood to the skin and exposing it to cooler air in the environment.
Higher levels of blood glucose can affect the osmolality of your plasma, which then impairs your body's ability to send blood to the periphery (skin) and to sweat.14 The challenge goes beyond feeling a little hot since it has a significant effect on your ability to experience deep sleep.
One study analyzed body temperature in people with Type 1 diabetes.15 The participants had their peripheral body temperature recorded for 10 consecutive days while awake and asleep. The researchers found thermoregulation alterations in the participants that led to shallow sleep.
They found during five hours of the day when it would be expected the body temperature would be the lowest, those with Type 1 diabetes had higher levels. They believed it “could be explained by less efficient heat dissipation.”16
The ability to get rid of heat during exercise is also important to maintain homeostasis and protect your life. Researchers have found those with higher levels of cardiovascular fitness may have an improved ability to dissipate heat during exercise.17
However, data show that even people with Type 2 diabetes who are relatively active have a significantly reduced ability to dissipate heat as compared to people without diabetes.
During a 60-minute exercise session, researchers found those with diabetes stored 1.54-fold more heat and had a lower evaporative heat loss.18 Additionally, those with diabetes kept greater amounts of heat in their body within the first 60 minutes after exercise had stopped.
Relationship Between Deep Sleep and Core Temperature
If you've ever woken up because you're too hot or cold, you know that ambient temperature affects your sleep quality. Even subtle differences in the temperature in the room or your core temperature can influence your sleep, for better or worse. Your body temperature cycles with your sleep-wake rhythm, decreasing at night while you're asleep and increasing during the day.19
Your core and peripheral skin temperatures are influenced by several factors, including your sleep environment, your clothing and blankets, mattress type, ambient room temperature and when you last ate. Increasing your skin temperature just 0.72 degrees F (0.4 degrees Celsius) can suppress nighttime wakefulness and shift your sleep into deeper stages.20
When fragmented sleep was measured subjectively in 765,000 people in the U.S., data showed that increasing nighttime temperature raised the number of self-reported nights of insufficient sleep.21 Other research also found that high temperatures affected objective and subjective factors of sleep and led to:22
- Reduced sleep duration
- Shallow sleep
- Lower sleep calmness
- Difficulty falling asleep
- Lower sleep satisfaction
Sleeping in a cooler room may therefore lead to fewer disruptions in your sleep. The National Sleep Foundation (NSF) suggests the ideal bedroom temperature is somewhere between 15.5 degrees C (60 degrees F) and 19.4 degrees C (67 degrees F).23 You want to avoid extreme temperatures (either too hot or too cold), as these could activate thermoregulatory defense mechanisms that cause you to wake up.24
A second reason to sleep in a cool room is the beneficial effect it has on brown fat. This type of fat generates heat by burning calories to help maintain your core temperature. Sleeping in a cool room (19 C or 66.2 F) for four weeks doubled the volume of brown fat in study volunteers, improving insulin sensitivity at the same time,25,26 which helps to improve your sleep quality.27
Shivering may be the mechanism that triggers brown fat to produce heat and burn calories,28 but shivering is not conducive to sleep. You are after the Goldilocks zone — cool enough to help you sleep and increase brown fat but not so cool that it makes you uncomfortable.
The exact best temperature will vary by individual but sleeping in a cool room with a thin sheet and blanket is generally enough to keep your skin temperature warm, so you feel comfortable, while still benefiting from the cool sleep temperatures.29
Deep Sleep Is Vital to Your Health
If you’ve been reading my newsletter, you know how important quality sleep is to your overall health. Dr. Zeeshan Khan, pulmonologist from the Deborah Heart and Lung Center, spoke with a reporter from KYW radio about sleep deprivation, the importance of quality sleep and the relationship to cardiovascular disease:30
“Almost every cardiac morbidity you can think of has been linked to sleep apnea. Heart disease, heart failure, arrhythmias, strokes, inflammatory issues like diabetes, worsening obesity — the list can go on and on.”
He recommends that on average, people should get seven hours of sleep each night, but he also shared that in America, about 35% of people get less than that. “We are kind of a sleep-deprived nation,” he said.31 This sleep deprivation also shows up as fragmented sleep, when you wake up during the night and sometimes have trouble going back to sleep.
Researchers at UC Berkeley studied 1,600 subjects to identify the effect fragmented sleep had on atherosclerosis. The authors believe the data is important since improving sleep quality may "represent one preventive strategy for lowering inflammatory status and thus atherosclerosis risk, reinforcing public health policies focused on sleep health."32
Another study demonstrated the importance quality sleep has on your cognitive health. Researchers from Italy showed astrocytes, a type of glial cell in the brain that gets rid of unnecessary nerve connections under normal circumstances, will start to break down healthy nerve synapses in response to chronic sleep deprivation.33
There is a high cost to sleep deprivation and low-quality sleep as it is also associated with an increased risk of accidents,34 higher potential for diabetes and high blood pressure35 and decreased life expectancy.36
Simple Body Hacks to Deep Sleep
One simple way of improving your sleep is to address your body’s core temperature. Dr. Dianne Augelli, a sleep disorder specialist at NY-Presbyterian/Weill Cornell Medical Center, says: “You don’t want to heat yourself up right before bed. Cooling down is a signal that tells us we’re supposed to go to sleep.”37
When you interrupt this process by eating late in the evening, and thus increasing your glucose and insulin levels and reducing your ability to dissipate heat, it can make the process of falling asleep more difficult and the potential of achieving deep sleep more challenging.
If you do happen to eat within three to four hours before falling asleep, consider taking a cool shower within an hour of going to sleep to help trigger a reduction in core body temperature.
It is important not to take a cold shower, as it can have the reverse effect as your body fights to maintain homeostasis. Taking a lukewarm shower, and towel drying slowly to allow heat to dissipate, may be all that's needed.
In addition to sleeping in a cool room with a thin sheet and blanket as I discussed above, you may consider the additional tips in “Top 33 Tips to Optimize Your Sleep Routine” to help you fall asleep faster and stay asleep.
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