How Does the Sun Impact Sleep?

woman trying to sleep in the heatPublished 7/1/2021


The arrival of summer comes with warmer days and increased daylight hours, which means vacations, more time outdoors and increased social life for most people. Many people are not aware, however, of how the summer sun impacts sleep as well as your wakeful hours.

How sunlight impacts sleep

We love the summer for its heat and longer days, but those characteristics can also influence our sleep and wakefulness. To be well-rested and alert during the day and to avoid the signs of sleep deprivation, it’s important to understand how increased sunlight impacts sleep and how to manage and alleviate the negative effects. Increased sunlight can disrupt our circadian rhythms, stress our thermoregulation system and put us at risk for sleep-disrupting sunburns and heatstroke.

Longer days and greater sunlight exposure

You’ve likely heard of circadian rhythm, the sleep and wakefulness clock of the body. The circadian rhythm is regulated by hormones that respond to exposure to light. This means that light exposure stimulates cortisol and serotonin to make you alert and wakeful during the day and that your body will produce melatonin in the evening as daylight fades to signal sleep. Longer daylight hours can disrupt this schedule and studies have shown that people generally sleep fewer hours in the summer compared to other seasons. If you have windows or receive extra sun in your bedroom in the morning, you might find that you’re waking up earlier than you’re used to and unable to go back to sleep. Increased evening light can delay melatonin production and therefore the onset of sleep. These factors may put you at risk to sleep less (or in very rare cases, having insomnia) than the CDC recommended amount of seven to nine hours and have a negative effect on the overall quality of your sleep. Bright summer light has its positives too. If you’re used to waking up in the winter when it’s dark out, you might find that you have comparably more energy and alertness during the summer. Exposure to bright light for the first hour of waking can boost your production of cortisol and serotonin so that you have a stronger alertness effect. Increased daylight and sun exposure is also shown to alleviate some symptoms of sleep-disrupting mood disorders, indirectly helping you sleep better.

Hotter evening temperatures

Temperature and thermoregulation are crucial to quality sleep. It’s not just about comfort during the night, but also about how your body follows thermoregulation cycles as a part of your circadian rhythm to promote sleep and wakefulness at the right times. As we approach sleep, our core cools by distributing its heat to the surface of your skin, so that you feel warmer when in fact your core temperature is steadily lowering.  With a relationship between temperature and sleep, you might find it more difficult to sleep during the summer heat. If your bedroom is too warm from the day, it might prevent your core from cooling off adequately. Don’t crank your air conditioning to cool your room as much as possible, though. Studies suggest that sleep quality is ideal between 82 and 90 degrees, with greater or lesser temperatures stimulating your body’s thermoregulation response and affecting sleep onset, duration, and quality.  Comfort is important to sleep quality, too. If your bedroom is too warm, you might experience sweat pooling on your skin and dehydration, leading to discomfort and poorer sleep quality.

Sunburns and heatstroke

While most people are eager to take advantage of the heat and light of summer, we know that being outside exposes us to potentially harmful UV rays. Overexposure to UV rays causes sunburns and lowers your body’s immune system effectiveness. This increased physiological stress can inhibit your ability to achieve quality sleep. Specifically, sunburns can be uncomfortable enough that it’s difficult to fall and stay asleep. In some cases, sunburns can prevent your body from cooling off through your skin adequately. When that happens, your core temperature becomes too high and you may reach a state of heatstroke. As we know of thermoregulation, core body temperatures are at a low in the evening to better facilitate sleep. This means that heat stroke could have a negative effect on your sleep onset, duration, and quality if your core temperature stays too high.

Tips to get better sleep in the summer

You can help mitigate the negative effects of the sun by following a few tips to fall asleep:

  • Limit your exposure to high UV rays, which typically occur midday
  • Wear a minimum of SPF 30 sunscreen and protective clothing and avoid sunburns
  • Dim indoor lights in the hours leading to sleep to promote melatonin production
  • Use blackout curtains if it’s too light out to sleep or to keep yourself from waking up too early
  • Cool down your sleeping environment with air conditioning, a fan, or by opening a window
  • Make sure to consume enough water and sodium during the day to prevent dehydration
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