Dictionary > Infradian rhythm

Infradian rhythm

infradian rhythm - definition and example

Infradian rhythm
n., plural: infradian rhythms
[in-frā’dē-ăn ridh’ŭm]
Definition:biological rhythm that is repeated longer than a 24-hour circadian day

What is the Infradian Rhythm?

An infradian rhythm is a type of biological rhythm that lasts longer than 24 hours, with a frequency of occurrence that is less than once a day. Infradian rhythms are regulated by a complex interplay of biological mechanisms, including hormonal fluctuations, environmental cues, and genetic factors.

The infradian rhythm exerts a significant influence on six distinct bodily systems, including the brain, metabolism, immune system, microbiome, stress response system, and reproductive system.

Often referred to as the body’s “second biological clock”, the infradian rhythm operates alongside the 24-hour circadian clock that both men and women experience. However, unlike the circadian rhythm (natural rhythm), the infradian rhythm is observed in individuals with female physiology in the form of a menstrual cycle.

menstrual cycle
Figure 1: Typical 28-day menstrual cycle. Image Credit: ConceptionAdvice.com.

Infradian rhythms can be observed in many different organisms, from plants to animals, and are involved in regulating a wide range of physiological and behavioral processes.

Examples of infradian rhythms in humans include the menstrual cycle or menstruation phase, which occurs for approximately 28 days on average and have distinct phases, and seasonal affective disorder (SAD), which is thought to be influenced by changes in daylight and occurs on a yearly cycle.

Infradian rhythms are an essential area of research in biology and physiology, as they play a critical role in regulating many physiological and behavioral processes. Understanding the mechanisms that underlie these rhythms can lead to insights into a range of health conditions, from menstrual disorders to seasonal affective disorders. (LLC, 2023)

Biology definition:
An infradian rhythm is a biological rhythm with a cycle longer than 24 hours. Infradian rhythms are usually associated with physiological processes such as the menstrual cycle in females, hibernation in animals, or seasonal breeding patterns in birds. These rhythms are controlled by internal biological clocks.

Biological rhythms pertain to the synchronized cyclic pattern demonstrated by an organism as its response to a particular stimulus. A biological clock that synchronizes with biological rhythm may be endogenous or exogenous. An endogenous type is one in which the internal biological clock is the one that controls it. An exogenous type is one that involves an external cue (i.e. zeitgeber). There are different types of biological rhythms: circadian rhythms, diurnal rhythms, ultradian rhythms, and infradian rhythms.
An infradian rhythm has a longer period than a circadian rhythm. The cycle is repeated more than the 24-hour circadian day. This is in contrast to the ultradian rhythm wherein it recurs in periods shorter than a day but longer than an hour. In infradian rhythm, the frequency is less than one cycle in 28 hours.

Table: Infradian Rhythm Versus Circadian Rhythm

Infradian Rhythm Circadian Rhythm
  • An infradian rhythm refers to a biological rhythm that has a period longer than 24 hours, such as monthly or yearly cycles.
  • These rhythms are regulated by internal timing mechanisms within the body and can be influenced by various factors, such as hormonal changes.
  • A circadian rhythm or the body’s cycle is a biological rhythm that has a period of approximately 24 hours.
  • These rhythms are typically regulated by external factors such as exposure to sunlight and changes in temperature, and they help to regulate various physiological processes such as sleep and hormone production.

Data Source: Shoaib Zaheer of  Biology Online

What Effect Does the Infradian Rhythm Have on Your Body and Brain?

The infradian rhythm influences various bodily and mental processes in significant ways, resulting in significant changes in brain chemistry, metabolism, cortisol levels, sleep patterns, and self-care needs. Here are some examples: (Vitti, 25 Oct 2021)

  • Brain Chemistry: Over a month, the infradian rhythm induces a 25% alteration in brain chemistry. This fluctuation can impact mood, cognitive function, and overall mental well-being.
  • Metabolism: Your metabolism varies predictably across the month, which means that your dietary and exercise needs should also change to optimize your metabolism and detoxify excess hormones.
  • Cortisol Levels: Cortisol levels are higher during certain phases of the infradian cycle. This means that pushing yourself through a tough workout might raise cortisol levels even higher, resulting in stress, inflammation, and balance hormonal disturbance.
  • Sleep Needs: Most women require more sleep than men due to their more complex brain structure, which takes longer to reset for cognitive tasks.
  • Self-Care Needs: People with female physiology tend to require less extreme self-care practices because their biology is more efficient.

Why is it important?

Infradian rhythms are important for several reasons.

  • First, they play a crucial role in regulating many physiological and behavioral processes, including reproduction, hibernation, migration, and mood. By understanding these rhythms, researchers can gain insights into the mechanisms that underlie these processes, which can help to inform the development of new therapies for a range of health conditions.
  • Second, infradian rhythms can be used as diagnostic tools for certain health conditions. For example, irregular periods or menstrual cycles can be a sign of hormonal imbalances, and monitoring the frequency and regularity of these cycles can help to identify underlying issues. Similarly, disruptions to seasonal rhythms, such as those seen in seasonal affective disorder, can be an indicator of mood swings and disorders and may require targeted interventions.
  • Third, understanding infradian rhythms can help to inform public health policies and strategies. For example, understanding the seasonal patterns of infectious diseases can help to inform vaccination campaigns and other public health interventions. Similarly, understanding the seasonal patterns of mood disorders can help to inform mental health interventions, such as light therapy for seasonal affective disorder.
  • Overall, infradian rhythms are important because they play a critical role in regulating many physiological and behavioral processes, they can be used as diagnostic tools for certain health conditions, and they can inform public health policies and strategies. By continuing to study these rhythms, researchers can gain a deeper understanding of the complex interplay between biology and environment, and develop new treatments and interventions to improve health outcomes.

What is an example of infradian rhythms?

Here are examples of infradian rhythms:

  • Menstrual cycle

An example of monthly infradian rhythm is the woman’s menstrual cycle. The menstrual cycle is a complex physiological process that occurs over approximately 28 days on average, although the length can vary between individuals. The cycle involves the interplay of hormone levels such as estrogen and progesterone, and it is regulated by the hypothalamus, pituitary gland, and ovaries.

The female body undergoes four distinct phases during the 28-day menstrual cycle, which are as follows:

  1. Follicular Phase: After the ending of periods this phase lasts for 7-10 days. During this time, the body prepares for ovulation by increasing estrogen production and thickening the uterine lining.
  2. Ovulatory Phase: This phase occurs in the middle of the menstrual cycle and lasts for approximately 4 days. It is characterized by the release of an egg from the ovary and the highest levels of estrogen in the cycle.
  3. Luteal Phase: This phase lasts for 10 to 14 days between ovulation and the start of the next period. During this time, the body produces high levels of progesterone to prepare the uterus for a potential pregnancy.
  4. Menstrual Phase: This phase lasts 3 to 7 days and is marked by the shedding of the uterine lining. It is the phase commonly referred to as the period.
hormone levels menstrual cycle
Figure 2: Hormone in the menstrual cycle. Image Credit: BlendSpace.

During these four phases, the body experiences fluctuations in hormones that affect various aspects of health, including body temperature, sleep cycle, energy levels, emotions, blood sugar, and cognitive function.

During the menstrual cycle, there are fluctuations in hormones such as estrogen and progesterone that can affect insulin sensitivity, leading to changes in blood sugar levels. For example, in the premenstrual phase, when progesterone levels are high, insulin sensitivity tends to be lower, which can cause blood sugar levels to rise. In contrast, during the follicular phase, when estrogen levels are high, insulin sensitivity tends to be higher, leading to lower blood sugar levels.

During the menstrual cycle, the uterus undergoes a series of changes in preparation for a potential pregnancy. The cycle begins with the shedding of the uterine lining, which is followed by the growth of a new lining in preparation for potential fertilization.

Midway through the cycle, an egg is released from the ovary in a process called ovulation. If the egg is fertilized, it will implant in the uterine lining and result in pregnancy. If the egg is not fertilized, the lining of the uterus will be shed, and the cycle will begin again.

During the menstrual cycle, serotonin levels may also be affected by premenstrual syndrome (PMS), which can cause symptoms such as mood swings, irritability, and anxiety. Women’s hormone fluctuates and there is a drop in serotonin levels during the premenstrual phase, which can contribute to these symptoms.

The infradian rhythm in women is regulated by hormones (estrogen and progesterone) which can be affected by factors such as excess hormones and diet. Fewer caloric intake for a few months can lead to weight loss, which impacts the menstrual cycle.

Eating a healthy diet that supports overall healthy women’s physiology is important, as is understanding how the infradian rhythm creates changes in the body throughout the menstrual cycle. Additionally, fat burning can be influenced by hormonal changes during the menstrual cycle, as well as diet and exercise habits. Eating foods rich in healthy fats, such as avocados and nuts, can help support a healthy infradian rhythm.

The menstrual cycle is an example of an infradian rhythm because it occurs over a period longer than 24 hours and has a frequency of occurrence that is less than once a day. It is regulated by various biological rhythms and mechanisms, including hormonal fluctuations, and is influenced by environmental and genetic factors. (Vitti, 25 Oct 2021)

Watch this vid about the menstrual cycle:

  • Hibernation in animals

Hibernation is an infradian rhythm that occurs in many animals, including bears, bats, and rodents. During hibernation, animals enter a state of torpor, characterized by a significant reduction in resting metabolic rate, heart rate, and body temperature. Hibernation is typically triggered by changes in food availability, temperature, and other environmental cues, and it allows animals to conserve energy during periods of low resource availability.

  • Seasonal affective disorder (SAD)

SAD is a type of mood disorder that is thought to be influenced by changes in daylight and occurs on a yearly cycle. Symptoms of SAD include low mood, irritability, fatigue, and changes in appetite and sleeping patterns. SAD is treated with various therapies, including light therapy, which involves exposure to bright light to regulate circadian rhythms and improve mood. (Chellappa & Cajochen, 2010)

  • Seasonal migration in birds

Many bird species migrate over long distances on an annual basis, in an infradian rhythm that is regulated by changes in day length, temperature, and food availability. Migration allows birds to access new food sources and breeding grounds, and it is thought to be influenced by a range of environmental and genetic factors. (Gwinner, 1996)

  • Menstrual cycle disorders

In some cases, the menstrual cycle may be irregular in terms of frequency or duration. Monthly menstrual cycle disorders can be a sign of hormonal imbalances or underlying health conditions and can be diagnosed and treated with various therapies, including hormonal contraceptives, lifestyle changes, or surgery.


How do animals synchronize their infradian rhythms with seasonal changes in food availability?

Answer: Animals can synchronize their infradian rhythms with environmental cues such as changes in day length, temperature, or food availability, which help them to adapt to seasonal changes in their environment. For example, some animals increase their food intake and store body fat in preparation for winter hibernation, while others adjust their reproductive cycles to coincide with the availability of food during certain seasons.

Take the Quiz!


Choose the best answer. 

1. What is infradian rhythm?

2. Typical sleep-wake cycle is an example of ....

3. Depicting infradian rhythm

4. In the menstrual cycle, the typical day in which the egg is released

5. Refers to the external or environmental cues regulating biological rhythms

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  • Britannica.com. (2023). hibernation. Retrieved 15 April 2023, from https://www.britannica.com/science/hibernation
  • Chellappa, S. L., & Cajochen, C. (2010). The circadian clock and the homeostatic hourglass: Two timepieces controlling sleep and wakefulness. The circadian clock, 195-228.
  • Gwinner, E. (1996). Circadian and circannual programmes in avian migration. The Journal of Experimental Biology, 199(1), 39-48.
  • Health, S. L. S. (2022). Infradian rhythm diet. Retrieved 15 April 2023, from https://www.stlukeshealth.org/resources/effects-of-the-infradian-rhythm-diet
  • Mindbodygreen.com. (2023). Infradian Rhythm. Retrieved 15 April 2023, from https://www.mindbodygreen.com/articles/what-is-our-infradian-rhythm
  • Healthline.com. (2023). Infradian Rhythm to Optimize Your Body’s Cycles. Retrieved 15 April 2023, from https://www.healthline.com/health-news/abortion-pill-mifepristone-remains-available-latest-court-ruling#The-bottom-line:
  • Vitti, A. (25 Oct 2021). Infradian Rhythm. Retrieved 15 April 2023, from https://www.floliving.com/infradian-rhythm/
  • Hedge, A. (2013). Biological Rhythms. Retrieved from http://ergo.human.cornell.edu/studentdownloads/dea3250pdfs/biorhythms.pdf
  • “Ultradian, adj.” Oxford English Dictionary. Retrieved from oed.com.
  • Brown, F. M. & Graeber, R. C. (1982). The Rhythmic Aspects of Behavior. Hillsdale, NJ: Lawrence Erlbaum Associates. p.462.

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