Biology and Medicine

Circadian Rhythms and Their Influence on Human Physiology and Disease

Michael Thompson^* Department of Chronobiology, University of Cambridge, Cambridge, United Kingdom
^*Correspondence: Michael Thompson, Department of Chronobiology, University of Cambridge, Cambridge, United Kingdom, Email:

Received: 04-Aug-2025, Manuscript No. BLM-25-30105; Editor assigned: 06-Aug-2025, Pre QC No. BLM-25-30105 (PQ); Reviewed: 20-Aug-2025, QC No. BLM-25-30105; Revised: 27-Aug-2025, Manuscript No. BLM-25-30105 (R); Published: 03-Sep-2025, DOI: 10.35248/0974-8369.25.17.788

Description

Circadian rhythms are intrinsic 24-hour cycles that regulate physiological, behavioral, and molecular processes in virtually all living organisms. Governed by the central pacemaker in the suprachiasmatic nucleus of the hypothalamus and peripheral clocks in various tissues, circadian rhythms synchronize internal biological processes with the external environment. These rhythms influence sleep-wake cycles, hormone secretion, metabolism, immune function, and gene expression, ensuring temporal coordination of physiological functions. Disruption of circadian rhythms is increasingly recognized as a significant contributor to metabolic disorders, cardiovascular disease, cancer, neurodegeneration, and mood disorders, emphasizing the relevance of chronobiology to human health [1-3].

At the molecular level, circadian rhythms are driven by transcriptional-translational feedback loops involving core clock genes such as CLOCK, BMAL1, PER, and CRY. These proteins regulate rhythmic gene expression across the genome, influencing downstream pathways that control cellular metabolism, DNA repair, and redox balance. Peripheral clocks in tissues such as liver, heart, pancreas, and adipose tissue enable localized regulation of metabolism and physiology, coordinating with the central clock to maintain systemic homeostasis. Disruption of these rhythms, whether through genetic mutations, environmental cues, or lifestyle factors, can lead to desynchronization and pathological consequences [4-6].

Metabolic health is intimately linked to circadian rhythms. Insulin secretion, glucose metabolism, and lipid processing exhibit diurnal variation, with misalignment contributing to obesity, type 2 diabetes, and metabolic syndrome. Night-shift work, chronic jet lag, and irregular sleep patterns disrupt circadian synchronization, increasing susceptibility to metabolic disorders. Animal studies demonstrate that altering feeding times to align with endogenous rhythms improves glucose tolerance, reduces weight gain, and enhances metabolic efficiency. These findings underscore the potential of chrononutrition and timed interventions in promoting metabolic health [7-9].

The cardiovascular system also exhibits circadian variation, with blood pressure, heart rate, and vascular tone fluctuating over the day-night cycle. Disruption of these rhythms is associated with increased risk of myocardial infarction, stroke, and arrhythmias. Clinical studies reveal higher incidence of acute cardiovascular events in the morning, reflecting circadian regulation of platelet aggregation, endothelial function, and sympathetic activity. Understanding circadian influences on cardiovascular physiology has implications for timing therapeutic interventions, known as chronotherapy, to enhance efficacy and reduce adverse effects.

Sleep regulation is a primary output of circadian rhythms, with significant consequences for cognitive function, mood, and overall health. Circadian misalignment contributes to insomnia, excessive daytime sleepiness, depression, and cognitive impairment. Emerging research links disrupted rhythms to neurodegenerative diseases such as Alzheimer’s and Parkinson’s, potentially through impaired clearance of toxic proteins during sleep. Melatonin, a hormone secreted by the pineal gland under circadian control, plays a central role in sleep regulation and circadian entrainment, with exogenous supplementation used therapeutically to treat sleep disorders and jet lag.

The immune system is also under circadian regulation. Leukocyte trafficking, cytokine production, and pathogen response exhibit daily rhythms, influencing susceptibility to infections and the timing of immune interventions. Disruption of circadian rhythms alters immune responses, contributing to chronic inflammation, autoimmune disease, and impaired vaccine efficacy. Chronobiology-informed approaches may optimize timing of vaccinations, immunotherapies, and antiinflammatory treatments to enhance outcomes [10].

Cancer biology has revealed profound connections between circadian rhythms and tumorigenesis. Core clock genes regulate cell cycle progression, DNA repair, and apoptosis, and disruption of circadian timing promotes uncontrolled proliferation and genomic instability. Epidemiological studies link shift work and circadian disruption to increased risk of breast, prostate, and colorectal cancers. Experimental models demonstrate that restoring circadian alignment can suppress tumor growth, and chronotherapy, involving timed administration of chemotherapy or radiation, can improve efficacy and reduce toxicity.

Neurobiology and cognition are also influenced by circadian timing. Learning, memory consolidation, and synaptic plasticity exhibit diurnal variation, while circadian disruption impairs cognitive performance and mood regulation. Circadian dysfunction contributes to mood disorders, including depression and bipolar disorder, through effects on neurotransmitter systems, hormone secretion, and neural connectivity. Targeting circadian pathways through behavioral, pharmacological, and light-based interventions represents a promising avenue for neuropsychiatric therapy.

Aging is associated with gradual deterioration of circadian regulation, manifesting as fragmented sleep, reduced amplitude of hormonal rhythms, and impaired metabolic control. This decline contributes to increased susceptibility to chronic diseases, cognitive impairment, and frailty. Interventions aimed at restoring circadian alignment, such as light therapy, timed feeding, and lifestyle modifications, may improve quality of life and reduce age-related morbidity. Recent research also explores pharmacological agents targeting clock proteins to modulate circadian function in aging populations.

References

1. Valderrabano P, McIver B. Evaluation and management of indeterminate thyroid nodules: The revolution of risk stratification beyond cytological diagnosis. Cancer Control. 2017;24(5).

   [Crossref] [Google Scholar] [PubMed]

2. Trimboli P. Advancements in Ultrasound and Ultrasound-Based Risk Stratification Systems for the Assessment of Thyroid Nodule. Cancers. 2022;14(7):1668.

   [Crossref] [Google Scholar] [PubMed]

3. Wang J, Wei W, Guo R. Ultrasonic elastography and conventional ultrasound in the diagnosis of thyroid micro-nodules. Pak J Med Sci. 2019;35(6):1526.

   [Crossref] [Google Scholar] [PubMed]

4. Tessler FN, Middleton WD, Grant EG, Hoang JK, Berland LL, Teefey SA, et al. ACR thyroid imaging, reporting and data system (TI-RADS): white paper of the ACR TI-RADS committee. J Am Coll Radiol. 2017;14(5):587-595.

   [Crossref] [Google Scholar] [PubMed]

5. Hasegawa J, Suzuki N. SMI for imaging of placental infarction. Placenta. 2016;47:96-98.

   [Crossref] [Google Scholar] [PubMed]

6. Kim DW, Jung SJ, Eom JW, Kang T. Color Doppler features of solid, round, isoechoic thyroid nodules without malignant sonographic features: A prospective cytopathological study. Thyroid. 2013;23(4):472-476.

   [Crossref] [Google Scholar] [PubMed]

7. Alexander EK, Kennedy GC, Baloch ZW, Cibas ES, Chudova D, Diggans J, et al. Preoperative diagnosis of benign thyroid nodules with indeterminate cytology. N Eng J Med. 2012;367(8):705-715.

   [Crossref] [Google Scholar] [PubMed]

8. Shuzhen C. Comparison analysis between conventional ultrasonography and ultrasound elastography of thyroid nodules. Eur J Radiol. 2012;81(8):1806-1811.

   [Crossref] [Google Scholar] [PubMed]

9. Bonacchi G, Becciolini M, Seghieri M. Superb microvascular imaging: A potential tool in the detection of FNH. J Ultrasound. 2017;20:179-80.

   [Crossref] [Google Scholar] [PubMed]

10. Jiang L, Zhang D, Chen YN, Yu XJ, Pan MF, Lian L. The value of conventional ultrasound combined with superb microvascular imaging and color Doppler flow imaging in the diagnosis of thyroid malignant nodules: a systematic review and meta-analysis. Front Endocrinol. 2023;14:1182259.

    [Crossref] [Google Scholar] [PubMed]