Circadian Rhythm is an internal and natural process that regulates a sleep-wake cycle repeated approximately every 24 hours. It may refer to a biological process featuring endogenous oscillation, an entrainable of approximately 24 hours.
The 24-hour rhythm is driven by circadian clocks, and this process has been widely observed in plants, animals, fungi, and cyanobacteria.
Sleep and metabolism do not work in isolation—they are closely connected to nutrition timing and food quality within a balanced nutrition approach, as explained in Healthy Eating Explained: The Evidence-Based Guide to Building a Balanced Diet for Life.
The term circadian is derived from Latin; circa, which means “around” (or “roughly”), and diēm, meaning “day”. Formal studies of temporary biological rhythms, such as daily rhythm, tides, weekly, seasonal, and yearly, are called chronobiology.
The process with a 24-hour oscillation is more commonly called a diurnal rhythm. In fact, it cannot be called a circadian rhythm unless its endogenous properties are confirmed.
Factors Affecting Circadian Rhythm
Circadian rhythm is found in humans, animals, plants, as well as microbes. The study of circadian rhythm is called chronobiology. The circadian rhythm is influenced by natural (endogenous) and environmental (exogenous) factors.
Endogenous (Natural) Factors
The circadian rhythm is controlled by a biological clock located in a small structure in the hypothalamus called the Suprachiasmatic Nucleus (SCN).
The SCN regulates the production of melatonin. At night, when light exposure decreases, melatonin levels rise and promote sleepiness. In the morning, exposure to sunlight suppresses melatonin, helping the body wake up and become alert.
Disruptions in this internal system can affect appetite regulation, energy balance, and weight control—one reason why many people struggle to understand why it is difficult to lose weight despite dieting or exercise.
Exogenous (Environmental) Factors
Several environmental factors influence circadian rhythm, including:
- Sunlight exposure
- Earth’s rotation
- Seasonal changes
- Ambient temperature
Lower ambient temperatures often promote deeper sleep, which explains why temperature changes can influence sleep quality and circadian alignment.
Circadian rhythm and biological clocks are distinct but interconnected. Biological clocks respond to environmental cues, allowing the body to adapt to changes in light, temperature, and daily routines.
Human Biological Clock: Daily Rhythm and Organ Activity
Biological clocks regulate physical, mental, and behavioral activities over a 24-hour cycle. These rhythms influence sleep, hormone production, digestion, and body temperature.
Note: The following schedule reflects traditional interpretations of daily body rhythms and should be viewed as general wellness guidance—not medical diagnosis or treatment.
07:00–09:00 — Stomach
Digestive activity is strong during this period. A nutritious breakfast supports energy production and metabolism efficiency.
11:00–13:00 — Heart
Avoid intense physical activity. The immune system is less active, and the body benefits from lighter tasks.
13:00–15:00 — Liver
Energy levels dip. Short rest periods may support liver cell regeneration and digestion.
15:00–17:00 — Lungs
Body temperature and adrenaline peak. This is an ideal time for exercise, which complements discussions in Diet vs Exercise: Which Matters More for Sustainable Weight Loss?
17:00–19:00 — Kidneys
Kidney function is strong. This period is often associated with learning and concentration.
19:00–21:00 — Stomach
Digestive capacity decreases. Heavy meals are best avoided.
21:00–23:00 — Spleen
Associated with detoxification and cellular regeneration. Fatigue or paleness may signal imbalance.
23:00–01:00 — Heart
The body focuses on recovery and energy restoration.
01:00–03:00 — Liver
Detoxification and cellular repair are most active. Quality sleep during this window supports metabolic health.
02:30–04:30 — Lungs
Cleansing processes occur. Coughing or sweating may happen as part of detoxification.
05:00–07:00 — Colon
Optimal time for bowel movements, supporting waste elimination and digestive health.
When circadian rhythm is consistently disrupted, it can also affect how the body absorbs and utilizes key nutrients, increasing the risk of certain micronutrient deficiencies over time.
Why Circadian Rhythm Matters for Daily Health
Disrupted circadian rhythm has been associated with:
- Poor sleep quality
- Hormonal imbalance
- Increased stress response
- Difficulty maintaining healthy eating patterns
This is why sleep timing, stress regulation, and consistent daily routines play an important role alongside nutrition and physical activity.
Bottom Line
Circadian rhythm is a foundational system that influences sleep, metabolism, digestion, and overall energy balance. When aligned with consistent routines, balanced nutrition, and healthy movement, it supports long-term well-being rather than quick fixes.
Understanding your circadian rhythm helps explain why sustainable health requires more than diet or exercise alone—it requires timing, consistency, and respect for how the body naturally functions.
Skincare Solutions & Skin Health
Mental Health, Stress & Emotional Wellbeing
Sleep, Energy & Daily Performance