You may have heard that things like eating or exercising before bed can result in worse sleep. You might not know why though…why does having food or doing some exercise cause our sleep to be worse?
In fact you might think having a nice comforting meal will relax you and working really hard physically before bed will make you more tired and make you sleep better.
Contrary to what might seem obvious, activities like eating and exercising can cause your sleep quality to suffer because it raises your body temperature.
If you are not sweating or even hot when going to bed how could this be true?
First we need to understand a little bit about why our body even cares about our body temperature to understand why.
Our body temperature is very tightly regulated.
There are certain processes that happen within our body to keep us alive that can only happen within a certain temperature range.
Our bodies are full of enzymes that assist with certain biochemical reactions to keep us alive, these enzymes will only function properly at a certain temperature. If the temperature is too hot or too cold the enzymes will denature, the reactions won’t happen, and we could be in a world of trouble.
In addition there are functions which happen within our cells, like protein synthesis and the generation of energy, which provides the fuel to our body. This process can only take place within a specific temperature range. The simple truth is if our cells can’t produce energy we die.
Our nerves also will not function properly if we get too hot or too cold so having a properly functioning nervous system is critical for our survival.
Then finally our body uses temperature to protect itself from viruses and pathogens. This is exactly what a fever is, the body raising its own temperature in order to kill the infection.
I am sure everyone reading this also is familiar with some of the ways the body tries to maintain its temperature.
When we get too hot we sweat. When the sweat evaporates it pulls heat away from the skin of the body, cooling us down.
When we get too cold the body can also produce its own heat. It does this by shivering. Shivering is essentially involuntary contractions of the muscles in your body.
How does that generate heat? The muscle contractions require the burning of stored glucose and fat to power the contractions, however this process of turning glucose and fat into muscle contractions is not perfect, some of the energy that is produced during that process is lost…and it’s lost in the form of heat.
In reality your body could care less about your muscles contracting, it’s just doing that so it can generate some heat to help warm you up!
Another common fact about our body’s temperature that you may know is that a normal human body temperature is 98.6 degrees Fahrenheit or 36.8 degrees Celsius. In reality this is not actually true, the optimal human body temperature is not a specific number, it’s a range between 97.7- 99.5 degrees Fahrenheit (Levine, n.d.).
This optimal range can fluctuate depending on the time of day, an individual’s age, their sex, and menstrual cycle (for females).
Regarding eating and exercising before bed, we really need to pay attention to the fact that our body temperature should fluctuate based on the time of day. Below is a nice graphic illustrating this general pattern in our body temperature throughout the day.
Notice in the graphic above that as night approaches our body temperatures should be dropping. If this doesn’t happen for whatever reason then it may not only disrupt your sleep but also have other negative effects.
A recent study done on 33 males and females who had some degree of insomnia showed the lowering of body temperature before bed had negative effects on their heart rate variability and resting heart rate in addition to getting less stage 3 sleep, aka deep sleep. (Core Body Temperature Changes Before Sleep Are Associated With Nocturnal Heart Rate Variability, 2023)
Not only did a disruption in lowering of their body temperature affect their sleep, but it also impacted indications of stress with lower heart rate variability and higher resting heart rates. I have written separate blog posts explaining why disruptions in resting heart rate and heart rate variability can lead to negative health outcomes, but to summarize here they are both related to an increase in stress. And as the graphic below nicely illustrates, stress is associated with numerous negative health outcomes.
Obviously I am not going to suggest that the only thing you need to do to have a perfect night of sleep is to make sure your temperature lowers before going to bed and avoid eating and exercising before bed is going to get you there.
That is simply not true, there are a lot of other things that contribute to the quality of your sleep besides your body temperature.
However sleep issues can be hard to navigate, as I just said sleep is complex, so I find nailing the things you can control and are obvious should be a no brainer if you are struggling with your sleep.
Your body temperature is one of those no brainers.
So yes, avoid eating and exercising in the hours leading up to bed, that will help make sure your body naturally lowers its body temperature before bed. There is the obvious suggestion of making sure the room you are going to sleep in is not too hot or too cold.
Between not exercising or eating before bed and making sure the temperature of your bedroom is comfortable that will get you 95% of the benefits.
However, there is one more thing you can try to do to make sure your body’s temperature is not too high before going to bed and that is getting your hands and/or feet warm. This might seem counterintuitive but what happens is that your body tries to cool your hands or feet because they are too warm and in the process cools down the rest of your body, dropping your body temperature. This can be accomplished by wearing gloves or socks or even by taking a warm shower in the hours leading up to bed.
I find simple actionable steps to improve health are the best way to get people to make meaningful lasting change and get closer to their goals. If something like just paying attention to the time you exercise or eat can drastically improve your sleep then that is a great way to keep you motivated and look for additional actionable steps you can take to make more change. This is the type of information I try to dispense each week via my newsletter. So if you are looking for more ways to make meaningful changes to improve your health without being overly complicated, sign up for my newsletter using the form below!
Core body temperature changes before sleep are associated with nocturnal heart rate variability. (2023, July 1). PubMed. Retrieved July 24, 2023, from https://pubmed.ncbi.nlm.nih.gov/37262106/
Levine, M. (n.d.). A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich. PubMed. Retrieved July 24, 2023, from https://pubmed.ncbi.nlm.nih.gov/1302471/