This March we will be adjusting as we adjust the clocks on their walls to “spring forward,” an hour. This is known as daylight saving time and was created so we could take advantage of longer daylight hours which come from a tilt of the Earth’s axis. It seems like the internal body clock adjustment should be just as easy as changing the clock on the wall, but usually it seems much more difficult. Why does the change effect our bodies so much? Circadian rhythms.
Changing the time on our clocks for daylight saving time is an easy adjustment, but our internal body clocks may take a little longer to reset since the time change interferes with our bodies’ circadian rhythms.
Research shows that circadian rhythms do not adjust immediately to daylight saving. Our bodies are made to naturally adapt to the changing seasons, and this rhythm is interrupted when we force ourselves to “spring forward.”
Our circadian rhythms are what govern biological activities in all plant and animal species. Included in these activities are metabolism, hormone levels, body temp, and when we feel the need to eat, sleep, and wake. This is about a 24-hour cycle, greatly impacted by external factors, especially the presence light and darkness, as well as a lack of these.
A large part of our circadian rhythms is our internal body clocks, also known as circadian clock. Our circadian clocks are naturally designed to move simultaneously with the changing environment and seasons. A slight change in this clock, even the seemingly small one hour change from daylight saving, is enough to throw off our circadian rhythms.
Hormone changes play a large role in throwing off our body clocks and interfering with sleep, especially melatonin and cortisol.
Setting our clocks forward in the spring may be even harder for our body clocks to reset than The spring time change can be even harder on our body clocks than the “falling back” change in the fall because melatonin is not produced until it becomes dark, so going to bed on schedule may be difficult until our bodies adjust.
The circadian clock is located in the suprachiasmatic nucleus (SCN), which is in the hypothalamus of the brain. There is one in each hemisphere just above the optic nerves which transfer information from the eyes to the brain. The SCN accepts information about the light coming in during the day, and lack of light at night. The lack of light is what triggers our brains to produce melatonin, making us sleepy.
Melatonin is one of the hormones that relies on the circadian clock and is produced by the pineal gland. It lowers body temperature and makes us feel sleepy so we are ready to go to bed. Daylight saving can interfere with melatonin production, which can make getting to sleep difficult.
Cortisol levels are also an important factor for the circadian clock. Cortisol is a hormone produced by the adrenal glands that regulate many of the body’s changes in response to stress.
Normally, cortisol levels are highest in the morning, making us alert for the day and gradually decrease as the day goes on. Cortisol is at its lowest at night, allowing us to sleep.
Cortisol levels in the body also naturally change with the seasons, increasing the most during the winter solstice. As the sunrise is delayed, cortisol levels increase. But daylight saving changes cortisol’s morning peak by a full hour and does not efficiently adjust to the hour change from daylight saving.
Some studies show it may take days to several weeks for our bodies to reset, and while we are waiting for this to happen, we may experience symptoms such as irritability, daytime fatigue, insomnia, and decreased immune function. Some researchers question if we ever actually reset from the time change.
These changes with melatonin and cortisol interrupt our sleep patterns, which as a result leads to poor quality sleep. And poor sleep quality can be harmful to health. But since we still have to change our wall clocks, we must also try and reset our body clocks. To make this easier, exercise regularly, keep your naps short, don’t eat too late in the evening, and avoid caffeine and alcohol later in the day.
Kantermann et al., The Human Circadian Clock's Seasonal Adjustment Is Disrupted by Daylight Saving Time, Current Biology (2007), dot: 10.1016/j.cub.2007.10.025
Monk, T. H., & Aplin, L. C. (1980). Spring and Autumn daylight saving time changes: Studies of adjustment in sleep timings, mood, and efficiency. Ergonomics, 23(2), 167-178. doi:10.1080/00140138008924730
Monk, T. H., & Folkard, S. (1976). Adjusting to the changes to and from Daylight Saving Time. Nature, 261(5562), 688-689. doi:10.1038/261688a0
Thomas, K., Juda, M., Merrow, M., & Roenneberg, T. (2007). The Human Circadian Clock's Seasonal Adjustment Is Disrupted by Daylight Saving Time. Current Biology, 17(22), 1996-2000. doi:10.1016/j.cub.2007.10.025