A new international study drawing on 73 million nights of data reveals that our sleep patterns are seriously shaped by the day of the week, the season, and where we live.
Working with sleep data from more than 116,000 adults across the globe, Flinders University sleep experts used insights from an FDA-cleared under-mattress device to track sleep duration and timing over 3.5 years.
Lead author, Dr Hannah Scott from FHMRI Sleep Health says the findings give a detailed look at how geography, seasons, and our day-to-day schedules quietly disrupt the way we sleep.
"Sleep patterns aren't just about habits – they're deeply connected to the environment around us," says Dr Scott.
"Our findings underscore the seasonal nature of human sleep, and that it is influenced by demographics and geography.
"Whether it's daylight hours, temperature, or our weekly routine, these external factors have a surprisingly strong influence on the quality and quantity of our sleep and wellbeing".
"Importantly, it is normal to experience variations in our sleep across the seasons and this seems partly driven by where we live."
Co-lead author, Dr Bastien Lechat , says that the study found that sleep schedules differ between weekdays and weekends, with most people catching up on between 20 to 35 minutes of lost sleep over the weekend.
"Whilst people stay up later at the weekends, going to bed on average 30 to 40 minutes later than weekdays, they are also sleeping in longer - up to 80 minutes - on Saturdays and Sundays," says Dr Lechat.
"These changes to sleep schedules might seem small but they can have a dramatic impact on our body clocks," he says.
Middle-aged adults, especially those between 40 and 60 years old, showed the largest changes in sleep duration between weekdays and weekends, likely due to balancing full-time work and family responsibilities.
This aligns with growing concerns that irregular sleep can be linked to adverse health.
Seasonal changes also play a bigger role than expected with people living in the northern hemisphere sleeping 15 to 20 minutes more in winter, while those in the southern hemisphere – including Australians – sleeping less during the summer months.
"Interestingly we found that the farther you live from the equator, the greater the seasonal variation in sleep," says Dr Scott.
"Australians living further from the equator, such as in southern regions like Melbourne or Hobart, may feel the impact of these seasonal shifts more acutely than those in the tropics," she says.
The study uncovered a subtle but steady drop in overall sleep across the study period, with people sleeping about 2.5 minutes less per night from 2020 to 2023 – a decline researchers speculate could be tied to the lingering effects of the COVID-19 pandemic.
Senior author, Professor Danny Eckert says that the study should serve as a wake-up call for public health messaging.
"Irregular sleep is more than just feeling tired – it's can be a health risk and understanding how our routines and environments affect sleep is a helpful step towards improving it," says Professor Eckert.
The research team says that while the study is one of the largest of its kind, it was skewed towards tech-savvy individuals who already use sleep monitoring devices, and other factors like pets, children, or sleeping partners were not accounted for.
"Still, the research marks a major step forward in understanding how human sleep is shaped by our surroundings – and it's a reminder for us to be mindful of the clock, the calendar, and even the seasons when it comes to getting a good night's rest," concludes Professor Eckert.
The article, ' Variations in sleep duration and timing: Weekday and seasonal variations in sleep are common in an analysis of 73 million nights from an objective sleep tracker' by Hannah Scott, Bastien Lechat, Kelly Sansom, Lucia Pinilla, Jack Manners, Andrew J K Phillips, Duc Phuc Nguyen, Sebastien Bailly, Jean-Louis Pepin, Pierre Escourrou, Ganesh Naik, Peter Catcheside and Danny J Eckert was published in the SLEEP journal. DOI: 10.1093/sleep/zsaf099
