People can experience sleep very differently depending on whether it is summer, autumn, winter or spring. This may seem obvious, but research finally confirms it. The discovery may help people with sleep problems as well as sleep researchers, who should consider seasonal variation in their research.
Most people know the feeling of waking up fresh and well rested in the morning. Most people also know how horrible they can feel when they get far too little and poor-quality sleep.
People can experience sleep differently between nights, and new research from Sweden shows that the season can affect the self-reported quantity and quality of sleep.
For example, the self-reports indicate that people are more likely to sleep more than 7 hours a night during the autumn, and people have the least trouble falling asleep in the spring.
Many people may recognize that their sleep has seasonal variation, but this is the first time that researchers have demonstrated it. This discovery not only affects you, me and our neighbours but also the researchers who study sleep. They need to consider the time of year when they ask trial participants to self-report their sleep patterns.
“The main point is that sleep is not fixed over the year but has clear seasonal variation. The research perspective is that this may help to explain why some studies find certain results when they investigate people’s sleep and other studies find other results. The reason may be that the researchers performed their studies at different times of the year,” explains a researcher behind the study, Christian Benedict, Associate Professor and Senior Researcher, Department of Neuroscience, Uppsala University, Sweden.
The research has been published in the Journal of Sleep Research.
Analysed sleep patterns of 19,000 people in Sweden
Christian Benedict studied data from a population cohort of 19,000 people in Uppsala and Malmö, Sweden who answered questions about their sleep.
The questions focused on sleep duration and quality, problems waking up early in the morning without being able to fall asleep again and other topics.
Since all the questionnaire responses were dated, Christian Benedict divided the responses into summer, autumn, winter and spring to determine whether the self-reported responses generally varied across the year.
“The idea for the study arose through discussions with colleagues about how many people experience seasonal influence on their sleep. This is especially true in the Nordic countries, since we are up late in the summer, because the days are long, and then the short days in the winter negatively affect many people’s mood. This made us think that that both the sleep quantity and quality reported and the timing of the responses could affect our results,” says Christian Benedict.
The people studied were 45–75 years old and this age group is relevant for sleep researchers, since this is the time in life when many people have trouble getting enough high-quality sleep.
The season influences the quantity and quality of sleep
The results suggested some interesting seasonal trends.
· Participants surveyed during the summer were more likely to report sleeping less than 7 hours than those interviewed in the autumn. The researchers used autumn as a reference, since they had the most responses from this season.
· Individuals interviewed in the winter were less likely to report early awakening than those interviewed in the autumn.
· Participants interviewed in the spring reported less difficulty in falling asleep and disturbed sleep than autumn interviewees.
· Self-reported long sleep duration, difficulty maintaining sleep or not feeling rested after sleep did not vary by season.
Doctors and researchers should consider seasonal variation in sleep patterns
Christian Benedict explains that the results may be significant in several contexts.
Doctors should consider seasonal variation if patients report disturbed sleep, and informing people about seasonal variation in sleep, in addition to other factors such as stress and children, may be important .
The results are also significant because researchers always compare their results with those of other researchers.
However, if one cohort is asked to self-report their sleep patterns in the summer and another is asked in the winter, they may report such different results that comparing them makes no sense.
“This may strongly influence the research and should be considered,” explains Christian Benedict.
Disturbed sleep associated with the development of many diseases
Christian Benedict also says that the results contribute to a rapidly developing field because researchers are becoming increasingly aware that sleep quantity and quality not only affect how we feel the next day but also many more aspects of our lives.
Research has determined that sleep quantity and quality may influence the risk of developing metabolic disorders such as obesity and diabetes, cardiovascular disease and nervous system disorders such as Alzheimer’s.
Researchers are thus not only interested in determining whether you sleep poorly but also why – since this influences your health.
The reason for the seasonal variation in sleep patterns may include changes in the quantity and quality of ambient light or work-related changes that affect sleep.
“Making research as precise as possible requires eliminating the factors that can create variation between data sets. We suggest that seasonal variation is an important factor in sleep research,” concludes Christian Benedict.