A Midsummer Night’s Dream
- Jaime K. Devine, PhD
- 17 hours ago
- 3 min read
Whether you’re a fan of Shakespeare[1] or a fan of pastoral horror movies starring Florence Pugh[2], you’ve heard of Midsummer before. Midsummer is a pagan European celebration of the summer solstice, or longest day of the year, in the Northern Hemisphere[3]. The solstice happens this year on June 21st, 2025[4]. Well, technically, the solstice isn’t the whole day, it’s the moment when the sun is farthest north in the sky. The exact moment of the solstice will occur at 02:42 UTC on June 21st, 2025, which will be 22:00 on June 20th here in Baltimore where I am writing this blog post.
What is special about the summer solstice day is that it is the longest day of the year in the Northern Hemisphere, in terms of daylight. According to timeanddate.com, Baltimore will experience equally long days (14 hours and 56 minutes of daylight) between June 16th and June 26th, 2025[5]. If you happen to be reading this blog post from the Arctic Circle, you can expect to experience 24 hours of daylight (known as polar day) through most of June. If you’re reading this blog post from Antarctica, then you can expect to be in the dark on June 21st. Anyone in the Southern Hemisphere will be experiencing winter during Midsummer, ironically. You can expect the least amount of daylight during mid-June.
So, what do these daylight extremes mean for our sleep? Light exposure is our strongest zeitgeber, or environmental cue that our bodies use to determine time of day. Light suppresses melatonin production[6]. Melatonin is a hormone that your body produces naturally in response to darkness that has a cascading effect on neurochemical activity that leads to sleep. Let me repeat that—your body produces melatonin naturally in the dark. Melatonin is not a sleep aid; it is a neurochemical signal that it is nighttime. If you have been taking over-the-counter melatonin supplements and sitting in a room full of bright lights wondering why you can’t fall asleep, hopefully a light bulb has just gone off (pun intended). Save your money and turn out the lights.
Hopping off my melatonin soapbox and back onto the topic of daylight, humans sleep less hours in the summer than they do during the winter. Plenty of scientific data and personal anecdotes support this finding, but I would like to highlight a recent report. A team of researchers from Australia and France published findings from an analysis of 73 million nights of data that explored seasonal variations in sleep[7]. Data were collected from over 120,000 individuals who used a Withings Sleep Analyzer under-mattress sleep sensor between January 2020 and September 2023. As shown in Figure 1 below, study participants hailed from across the globe, including North America, South America, Europe, Asia, Africa, and Australia. Parts of Africa are not represented, and Antarctica isn’t even on the map, but this is impressive global representation in a dataset!
Figure 1. Geographical distribution of participants. Reprinted from Scott et al. 2025, Sleep.
The study used June 21st as the reference for longest and shortest sunlight day in the northern and southern hemispheres, respectively. Sleep duration was shortest during summer months in both the northern and southern hemispheres by 15 to 20 minutes. Bedtimes and wake times were later during summer months in both hemispheres as well, with the exception of December/January. It seems that everyone in the world stays up late and sleeps in during the holidays. You can read our blog post about how December holidays disrupt sleep here.
So, are these daylight extremes bad for your health? My advice is not to worry about seasonal variation in sleep duration when there are so many more disruptive factors affecting your sleep. You know the usual culprits— work schedules, life stress, undiagnosed sleep disorders, revenge bedtime procrastination[8], uncomfortable bedroom environment, alcohol, caffeine, or other substances, endlessly staring into the social media void that is your phone… A little extra sunlight is nothing compared to these.
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