The rhythm of life: how body temperature reveals our metabolic harmony

Finnish biohacker unveils the vital connection between circadian cycles and wellbeing at Tokyo summit

In a presentation that bridged Nordic philosophy with Japanese sensibilities, biohacking researcher Antti Immonen explored the intersection of biological rhythms, metabolic health and the Finnish concept of "vire" at the Hololife Summit 2025 in Tokyo. Speaking to an audience intrigued by the cultural resonance between Finland and Japan, Immonen outlined how continuous body temperature monitoring could revolutionise our understanding of daily metabolism.

Beyond health: the concept of thriving

The term "vire", which has no direct English equivalent, encompasses a state of vitality, being in tune with one's body, environment and others. Immonen, who founded his company around this multifaceted concept, explained that it represents something beyond mere health. "Vire means a state of vitality, being in tune with your body, your environment, and others. It's about thriving, not just being healthy," he said.

Drawing parallels with Zen philosophy, Immonen suggested that modern health optimisation has become unnecessarily anxious and overcomplicated. Instead, he advocated for a return to listening to the body's natural signals, describing life as "surfing invisible waves—predictable biological rhythms guide us, and our mindset directs how we ride them."

The body as prediction machine

Immonen described the human body as a hormonal prediction machine, constantly anticipating cycles of wakefulness and rest aligned with natural rhythms. These cycles operate at multiple timescales: infradian rhythms such as menstrual cycles, daily circadian rhythms, and shorter ultradian rhythms lasting minutes to hours.

The presentation drew attention to the powerful role of cortisol and melatonin in regulating these cycles. The morning cortisol surge prepares the body for wakefulness, whilst melatonin onset signals the approach of sleep. When these rhythms fall out of sync, the consequences extend beyond tiredness. Research cited by Immonen showed that circadian misalignment can reduce reaction time and cognitive function by 20 to 30 per cent, with recovery taking days.

Using the metaphor of seasons, Immonen described how each day contains its own cycle: morning as spring (eager awakening), day as summer (peak performance), evening as autumn (reflection and calm), and night as winter (rest). Disrupting this internal seasonal pattern through mistimed meals or irregular sleep leads to what he termed chronometabolic misalignment.

Temperature as metabolic compass

The centrepiece of Immonen's presentation was the proposition that continuous core body temperature monitoring offers a practical window into metabolic state and circadian rhythm. Unlike melatonin measurement, which requires laboratory analysis, body temperature can be tracked continuously and non-invasively.

"Your body is a hormonal prediction machine, constantly anticipating cycles of wakefulness and rest aligned with natural rhythms," Immonen explained. Core temperature reflects the sum of hormonal momentum throughout the day, rising during wakefulness and activity, falling during sleep. This pattern results from the combined influence of intrinsic circadian rhythm, sleep-wake cycles, and physical activity.

The practical applications are significant. Higher pre-sleep body temperature correlates with poorer sleep quality, whilst lowering core temperature before bed enhances deep, restorative sleep. During deep sleep, body temperature dips; during REM sleep, it rises slightly. A rapid, smooth transition from night to day temperature patterns signals healthy metabolic function, comparable to swift acceleration onto a motorway.

Environmental influences and interventions

Immonen shared personal data demonstrating how travel disrupts temperature rhythms, with recovery taking several days. Jet lag, he explained, reflects the suprachiasmatic nucleus—the brain's master clock—struggling to realign with new environmental cues.

The presentation also explored behavioural interventions. Cold exposure can elevate alertness by raising body temperature defensively, whilst warming the body (through sauna use, for example) can paradoxically lower core temperature by opening blood circulation. Evening warmth promotes the characteristic sleep pattern of cool core and warm extremities, reversing the daytime pattern of hot core and cool hands.

Metabolic coherence and timing

A recurring theme was the importance of smooth metabolic transitions. Immonen argued that metabolic coherence requires moving from one metabolic event to another without abrupt disruption. The concept challenges the notion that laziness or unproductivity stem from character flaws, suggesting instead that they often reflect chronometabolic misalignment.

"Balance and rhythm are foundations of vire: balance your metabolism, mental and physical load, and keep your body's natural rhythms in harmony," he stated. This framework emphasises not just what we do, but when we do it. Eating at the wrong circadian time, for instance, can undermine weight loss efforts, whilst working during an ultradian dip or circadian trough impairs performance.

Individual variations and practical wisdom

The presentation acknowledged substantial individual variation in circadian rhythms. Extreme morning and evening chronotypes can differ by as much as six hours in their internal "four seasons", meaning that optimal timing for meals, exercise and cognitive work varies considerably between people.

Immonen's vision for practical application centres on accessible monitoring. "Tracking continuous body temperature reveals your internal rhythms, helping you do the right things at the right times to enhance your metabolism and performance," he noted. By making temperature data actionable, individuals could potentially optimise daily metabolism with the same sophistication that heart rate variability monitoring has brought to sleep recovery.

The momentum of health

Drawing his presentation to a close, Immonen returned to the metaphor of momentum. Like a swing, circadian rhythms gain strength through regularity and consistency. When momentum is lost—when cortisol, melatonin and temperature amplitudes become desynchronised—the consequences accumulate. Fatigue deepens, ageing accelerates, and metabolic disorders become more likely.

The solution, in Immonen's view, lies not in complex interventions but in respecting biological rhythms. "Living life is like riding a bicycle—you need to keep moving," he observed, emphasising direction, balance and rhythmic continuity.

The concept of vire, with its emphasis on attunement and thriving rather than mere survival, offers a philosophy suited to an age of chronic stress and disrupted rhythms. By listening to the body's temperature rhythms and aligning behaviour accordingly, Immonen suggested, we can restore the metabolic and psychological harmony that characterises true vitality.

As he concluded his presentation, Immonen invited attendees to learn more about practical temperature monitoring, positioning the approach as a new frontier in personalised health optimisation. In the spirit of vire, the goal is not anxious perfection but harmonious alignment with the invisible waves that guide daily life.

Frequently asked questions

What does the Finnish word vire mean?

Vire has no direct English equivalent. Antti Immonen, who founded a company around the concept, described it as a state of vitality, of being in tune with your body, your environment and others. His point is that it names thriving rather than merely being healthy.

Why track core body temperature?

Immonen argued that core temperature offers a practical window into metabolic state and circadian rhythm, because unlike melatonin it can be tracked continuously and non-invasively. Temperature reflects the sum of hormonal momentum through the day, rising during wakefulness and activity and falling during sleep.

What does circadian misalignment cost?

Immonen cited research showing that circadian misalignment can reduce reaction time and cognitive function by 20 to 30 per cent, with recovery taking days. He framed each day as its own set of seasons, and mistimed meals or irregular sleep as chronometabolic misalignment rather than a character flaw.

About the event

This recap is part of the HOLOLIFE Summit 2025 Tokyo series, recorded in Tokyo on 10 and 11 October 2025. Read the summary of the whole event or join the next edition, HOLOLIFE Summit 2026 Amsterdam, on 14 and 15 November 2026.