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Mouse mitochondria run on AM–PM rhythms rather than 24-hour cycles

January 12, 2026 Circadian Biology Newsletter Issue #19

This week brought surprising discoveries about how our internal clocks actually work—and what happens when they don't. From mice revealing that metabolism runs on 12-hour rhythms to massive studies linking shift work with heart damage, the science is rewriting what we know about biological time.

🕐 Mouse liver runs on 12-hour cycles, not 24-hour ones

  • Male mice showed that most liver metabolic functions—especially carbohydrate and fatty acid processing—follow 12-hour rhythms rather than the expected 24-hour circadian cycles

  • This 12-hour rhythmicity accounts for 25-50% of overall metabolic variability and closely aligns with when nutrients are available throughout the day

  • Mitochondrial activity also fluctuates on these shorter cycles, suggesting the liver adapts energy production twice daily to match the body's changing demands

Why it matters: This challenges the fundamental assumption that biological clocks are primarily 24-hour systems and suggests our metabolism is more precisely tuned to meal timing than previously understood.

🥉 Top 5% journal 🔗 Cellular and molecular life sciences : CMLS Journal Article 🗓️ Jan 9

Key Findings

🫀 Shift work directly damages heart tissue in animal studies

  • Meta-analysis of 32 animal studies found that circadian disruption causes significant cardiac hypertrophy, with left ventricle-to-body weight ratios increased substantially

  • Both genetic clock gene knockouts and environmental disruption (like light phase shifts) led to pathological heart remodeling and elevated stress markers

  • The heart damage occurred at both organ and cellular levels, with enlarged heart muscle cells and increased fibrotic markers

💡 Animal evidence suggests shift work may directly cause structural heart damage, not just increase cardiovascular risk factors.
🥉 Top 5% journal 🔗 BMC medicine Journal Article 🗓️ Jan 9

🌙 Evening people face 84% higher prostate cancer risk from night shifts

  • Meta-analysis of shift workers found that those with evening chronotypes had 84% higher prostate cancer risk compared to day workers

  • Each additional year of night shift work increased prostate cancer risk by 2.1% specifically for evening chronotype workers

  • Morning chronotype shift workers also showed increased risks for breast cancer and mental health problems, suggesting chronotype matching doesn't protect against shift work harms

💡 Evening chronotypes may be particularly vulnerable to night shift health consequences, with dose-dependent cancer risks.
🥉 Top 5% journal 🔗 Scandinavian journal of work, environment & health Journal Article 🗓️ Jan 7

🧠 Night shift drivers show early heart damage and gut changes

  • 66 night shift ride-hailing drivers had significantly higher NT-pro-BNP levels (49.8 vs 41.3 pg/ml) compared to 175 day shift drivers—a marker of early heart stress

  • Night shift workers showed 20 different gut microbiome changes, with 4 bacterial taxa specifically linked to heart injury markers

  • The gut microbiome alterations correlated with cardiovascular biomarker changes, suggesting a possible gut-heart connection in shift work damage

💡 Night shift work may trigger measurable heart damage and gut disruption even before clinical symptoms appear.
🎖️ Top 10% journal 🔗 Environmental research Journal Article 🗓️ Jan 10

🧬 Circadian imbalance genes predict diabetes and mood disorders

  • Genome-wide study of 312,935 people identified 27 genetic loci linked to circadian imbalance, including known clock regulators like CALCA and CRX

  • People with higher circadian imbalance genetic scores showed increased risks for type 2 diabetes, major depression, and obesity

  • Genetic analysis suggested that circadian disruption may actually cause diabetes, mood swings, and heart attacks—not just correlate with them

💡 Your genetic predisposition to circadian disruption may directly influence your risk of major chronic diseases.
🔗 Research square Preprint 🗓️ Jan 9

💊 Timing thyroid cancer treatment to evening may boost effectiveness

  • Thyroid-stimulating hormone (TSH) naturally peaks overnight, but current radioactive iodine therapy protocols ignore this circadian rhythm

  • Since TSH drives the sodium-iodide symporter that helps thyroid cells absorb radioactive iodine, evening dosing could align with peak TSH levels

  • The theory suggests evening treatment timing could enhance iodine uptake, improve cancer-killing effects, and reduce whole-body radiation exposure

💡 Simply changing when thyroid cancer patients take radioactive iodine—from morning to evening—could make treatment more effective.
Top 50% journal 🔗 World journal of experimental medicine Review 🗓️ Jan 7

🐟 Clock genes control antiviral immunity in zebrafish

  • Zebrafish with mutations in circadian genes cry1a and cry1b showed increased viral loads and reduced survival when infected with Tilapia lake virus

  • cry1a mutants had lower initial expression of antiviral receptor tlr22, while cry1b mutants showed reduced antiviral gene Mxa expression later in infection

  • Both mutant lines also showed altered behavior (increased activity) and disrupted gut microbiomes, particularly more Proteobacteria in cry1a mutants

💡 Circadian clock genes may directly regulate how well vertebrates fight off viral infections.
Top 20% journal 🔗 Fish & shellfish immunology Journal Article 🗓️ Jan 6

Implications

The evidence is converging: our internal clocks don't just tell time—they actively protect our health through precise metabolic and immune coordination. When these rhythms break down from shift work or genetic variants, the damage appears to be direct and measurable, from heart tissue changes to weakened antiviral defenses.

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