Many people are familiar with the term “circadian rhythm.” Circadian rhythm controls the behavioral, physical, and mental changes that happen in your body over a roughly 24-hour period. Circadian rhythm is most often cited in the context of sleep, but hunger, energy levels, and mood are all strongly influenced by circadian rhythms, too.
There are also rhythms that last longer than a day. Known as infradian rhythms, these longer cycles can last for a month, a season, or even a full year (circannual rhythms).
Some examples include seasonal depression during periods of less daylight, bursts of energy when it starts to warm up in spring, and even animal hibernation and migrations. One of the most commonly known infradian rhythms is the monthly menstrual cycle.
Though the sleep space has long focused on circadian rhythms, more sleep specialists are coming to understand that sleeping well and waking rested means understanding our infradian rhythms as well.
What is infradian?
Dr. Chris Winter, neurologist, Sleep.com Sleep Advisor, and author of The Rested Child and The Sleep Solution, says that the term comes from the Latin words “infra,” meaning “longer than” and “dian,” for day. Therefore, infradian rhythms are defined as any cycles that last for more than a day. (In contrast, ultradian rhythms recur multiple times within a 24-hour period, and can include cycles of digestion, heart rate, and sleep cycles.)
“Rhythms are what the body is built on. They’re different names for the fact that our bodies don’t really do anything accidentally,” Winter says.
Although infradian rhythms are distinct from our circadian (or daily) rhythms, these two processes do interact. These interactions help to explain why as many as 90% of people who menstruate report fatigue in the days leading up to their periods, and the U.S. National Sleep Foundation reports another 30% say they have trouble sleeping in the week leading up to their period.
Understanding how these processes interact in general and in your body specifically can help you learn to work with your natural cycles rather than against them.
Infradian rhythm and the menstrual cycle
The menstrual cycle typically lasts for 28 days and is controlled by the ebb and flow of four major hormones:
- Follicle-Stimulating Hormone - Made by the pituitary gland in the brain, FSH helps immature egg cells to begin the final steps towards release.
- Luteinizing Hormone - Also made by the pituitary, LH signals the final step in egg maturation, when the mature ovum is released (aka, ovulation).
- Estrogen - Produced by the ovaries, adrenal glands, and fat cells, estrogen thickens the walls of the uterus to provide nutrients for an implanted fertilized egg.
- Progesterone - Works with estrogen to thicken the lining of the uterus.
Each phase of the menstrual cycle coincides with the increases and decreases of these four hormones. They all interact with neurotransmitters like serotonin and dopamine to affect everything from resting metabolic rate to mood to immune function.
In the luteal phase that immediately follows ovulation, circadian rhythms are more blunted. This means the body’s basal temperature (temperature when you’re fully at rest) and levels of melatonin (hormone that makes you sleepy) don’t fluctuate during the day.
“When there’s less contrast between the peak and the trough, sleep tends to be a little bit worse because our best sleep happens when all of our rhythms are very contrasting,” says Jade Wu, Ph.D., a behavioral sleep scientist at Duke University and Sleep.com Sleep Advisor.
At the beginning of the menstrual cycle (the first day of bleeding), low levels of estrogen and progesterone also lead to a reduction in serotonin, a neurotransmitter that affects learning, memory, and mood. Scientists have found that serotonin levels decrease throughout the menstrual cycle as estrogen declines, and that individuals with lower serotonin are more likely to report feelings of depression, anxiety, and fatigue in the days before their periods.
Other health conditions influenced by infradian rhythms
Infradian rhythms influence more than just how people feel during their menstrual cycles. A variety of health conditions are affected by infradian rhythms, including:
- Irritable bowel syndrome
- Cardiovascular disease
How to track your infradian rhythm
Although many of us would love to always feel at our peak (*raises hand*), that’s not realistic. Sometimes, we feel lousy for short periods of time due to easy-to-understand reasons, such as a cold, a looming deadline at work, or a fight with a partner. Other times, we can feel sluggish and exhausted for what seems like no good reason.
In those instances, tracking your infradian rhythms can help you figure out how to work with your body rather than against it, Wu says. Many reproductive-age individuals track their menstrual cycles, often to avoid or pursue pregnancy, or to know when to expect “Aunt Flow.” Tracking the days of a period is a good start, Wu says, but you don’t need to stop there. She also recommends tracking sleep, energy level, mood, or anything else you might be concerned about.
The Android and iPhone app stores each carry a variety of tracking apps, both free and paid, which can help with tracking cycles and related issues.
Some apps will provide diet and exercise advice for a fee, which is tailored to match your infradian rhythm. Although there’s no data showing that this information is harmful, there’s also not much research that shows a clear benefit.
Prefer a more analog experience? Use a bullet journal or paper planner, or even a plain notepad.
How to manage your infradian rhythm
Once you’ve started tracking your infradian rhythms, you can also experiment with different types of physical activity or different eating patterns to see how they affect your mood, energy levels, and sleep. Feeling really tired? Try a rejuvenating yoga session or quiet walk outside instead of pushing high-intensity cardio for physical activity. Mood lower for no specific reason? Maybe changing the way you’re eating will make a difference. By tracking these over the course of a cycle, you can identify any patterns.
Annual changes in sleep and mood, such as feeling more sluggish and tired in dark, frigid winter months, can be harder to track than monthly shifts but are no less important. Monthly changes might be more acute at specific times of the year.
The idea, Wu says, isn’t to try and find the perfect lifestyle hack to let you operate at 100% all the time. Rather, it’s to understand more about what your body is telling you about what it needs to feel good, and to understand more about what might make you tick. Instead of beating yourself up for feeling dead tired or being extra hungry, you can instead remind yourself that this is just part of your body’s natural cycle.
“When we look at rhythms and at the bigger picture, we can actually influence our sleep and our health — even our mood — a lot more than we think,” Wu says.
Keep your cycle on track
Both Wu and Winter say that one of the best ways to tune into your infradian cycle is by keeping certain factors consistent, such as eating regular meals. Just as important? Going to bed and getting up at the same time every day so you get enough sleep every night. Yes, even weekends. Maintaining a solid baseline, Wu says, will help you tune into your body’s ebb and flow.
Think of it like a symphony, Winter says. “You can listen to each instrument individually, but in order for the orchestra to work, they have to be synchronized and timed properly. And that’s really where good health comes from,” he says.