Ultradian Rhythms

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Ultradian rhythms are biological cycles that repeat multiple times within a 24-hour circadian day. They have a shorter period and higher frequency compared to circadian rhythms, which complete one cycle daily.

Examples of Ultradian Rhythms

Some key examples of ultradian rhythms in the human body include:

  • Sleep cycles - the 90-120 minute cycling through stages of light sleep, deep sleep, and REM sleep throughout the night
  • Hormone secretion - the pulsatile release of hormones like growth hormone, cortisol and insulin, essential for regulating metabolism, energy and stress
  • Heart rate and blood circulation
  • Breathing and thermoregulation
  • Brain wave activity
  • Blinking, appetite, arousal, and bowel activity
  • Urine and feces excretion, digestion
These ultradian rhythms, with periods ranging from minutes to hours, coordinate various physiological processes and behaviors in the body. They likely serve functions like energetic optimization and internal synchronization. Understanding these short-term biological cycles provides insight into the body's intricate timekeeping mechanisms.

Relationship Between Ultradian Rhythms and Hormonal Release


Ultradian rhythms have a strong relationship with the pulsatile release of various hormones in the body:
  • Hormones like growth hormone, cortisol, and insulin exhibit ultradian patterns of secretion, with pulses occurring every 90-120 minutes
  • ACTH (adrenocorticotropic hormone) release from the pituitary gland also follows both circadian and ultradian rhythms in rats
  • The ultradian rhythmicity of free corticosterone (the main glucocorticoid hormone in rodents) is highly synchronized between the blood, subcutaneous tissue, and brain
  • Spectral analysis has shown that pulses in prolactin and growth hormone are positively linked to increases in delta wave activity during sleep
  • In contrast, pulses of thyroid stimulating hormone (TSH) and cortisol are related to lighter stages of sleep

These findings demonstrate the tight coupling between ultradian hormone release patterns and various physiological processes like sleep, metabolism, and stress response. Disruption of these rhythms may contribute to hormonal imbalances and associated health issues.

Beat by Beat: A Journey Through Ultradian Rhythms

Chetna's eyes fluttered open as the first rays of dawn peeked through her bedroom window. She glanced at the clock - 6:15 am. Like clockwork, her body had awoken naturally, right on schedule.
Chetna smiled to herself, knowing that her internal circadian rhythm was finely tuned. But as she got up and started her day, she was unaware of the even more precise rhythms that governed her body on a shorter timescale - her ultradian rhythms.
Ultradian rhythms are biological cycles that occur multiple times per day, as opposed to the 24-hour circadian rhythms. One of the most well-known ultradian rhythms is the 90-120 minute basic-rest activity cycle (BRAC). This cycle alternates between high and low frequency brain waves, and is associated with periods of high and low alertness.
As Chetna ate breakfast, her BRAC was in a high frequency, high alertness phase. Her brain was firing on all cylinders, ready to tackle the day's tasks. But unbeknownst to her, her body was already preparing for the next low frequency, low alertness period.
At work, Chetna powered through her morning, riding the wave of her ultradian rhythm. But by 11am, she started to feel her energy waning. She yawned and her eyelids felt heavy. It was time for a break.
Chetna stepped outside for some fresh air and a quick walk around the block. As she moved her body, her brain released endorphins that boosted her mood and alertness. By the time she returned to her desk, she felt refreshed and ready to dive back into work.
This pattern repeated itself throughout the day. Chetna's ultradian rhythms ebbed and flowed, driving her periods of high and low energy. When she honored these rhythms by taking breaks and moving her body, she was able to stay productive and focused. But when she ignored the signals and tried to power through, she found herself fatigued and unfocused.
As evening approached, Chetna's ultradian rhythms began to shift again. Her body started producing melatonin, the sleep hormone, in preparation for bedtime. Her brain waves slowed down and her body temperature dropped. By 10pm, Chetna was sound asleep, her brain cycling through the stages of sleep in sync with her ultradian rhythms.
Throughout the night, Chetna's brain and body continued to dance to the rhythm of her ultradian cycles. She cycled between REM and non-REM sleep, her brain waves rising and falling. By 6:15am, she was ready to start the cycle all over again.
As Chetna got up and started her day, she marveled at the incredible complexity of the rhythms that governed her body. From the 24-hour circadian clock to the 90-minute ultradian cycles, her body was a symphony of biological rhythms. And when she honored those rhythms by living in sync with her body's natural cycles, she found that she could thrive and flourish.

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